The perception of egocentric distances in virtual environments - A review
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paper_title: A CAVE-like environment as a tool for full-size train design

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Simulations of models, in all different areas, is an expanding, attractive line of work. More and more applications are taking advantage of the improvements in technology and knowledge in this field, thus achieving results that would have been impossible to achieve with a real model, or foreseeing facts that otherwise would have been encountered too late in the production process. The rail industry is one possible beneficiary of this approach. Usually, before commencing the fabrication process of a new train, the construction of a full-size model is mandatory. Instead of building this full-size real model, which leaves little room for later, last-minute modifications, a virtual model can be built in the digital realm, thus offering a new platform for easier interaction with it. In this article, a simulation of a train is presented in order to tackle visual, aesthetic and ergonomic issues. The simulation runs on a PC-based CAVE-like architecture, offering a certain degree of interaction to the user, and combines static and dynamic computer-generated imagery, both with and without stereoscopy for 3D visualisation, as well as augmented virtuality techniques for the integration of the train with its environment.
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paper_title: Large displays in automotive design

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Explores the traditional and current uses of large displays in automotive design and presents new applications that make innovative use of large-format electronic displays. The development of our applications has highlighted several issues and challenges for the future. Perhaps the overriding issue is that, ultimately, the story is about interaction, not displays. For the system to be of value, it's generally not enough simply to present information. Viewers must be able to create, manipulate, explore and annotate the displayed image. Furthermore, the display's location, who uses it, what it's used for and how it's used are all critical in determining value.
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paper_title: Viewing geometric protein structures from inside a CAVE

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We have developed general modeling software for a Cave Automatic Virtual Environment (CAVE); one of its applications is modeling 3D protein structures, generating both outside-in and inside-out views of geometric models. An advantage of the CAVE over other virtual environments is that multiple viewers can observe the same scene at the same time and place. Our software is scalable-from high-end virtual environments such as the CAVE, to mid-range immersive desktop systems, down to low-end graphics workstations. In the current configuration, a parallel Silicon Graphics Power Challenge supercomputer architecture performs the computationally intensive construction of surface patches remotely, and sends the results through the I-WAY (Information Wide Area Year) using VBNS (Very-high-Bandwidth Network Systems) to the graphics machines that drive the CAVE and our graphics visualization software, Valvis (Virtual ALpha shapes VISualizer).
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paper_title: Training in peacekeeping operations using virtual environments

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Proper training of military personnel, at all levels, has never been more crucial. In this article, we describe the application of virtual environment technology to a novel and complex task-the military checkpoint. In the process, we also address differences between an immersive virtual environment training system and a destop version.
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paper_title: Sidh - a Game Based Firefighter Training Simulation

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This paper presents Sidh-a game based firefighter training simulator developed in cooperation between the University ofSkvde and the Swedish Rescue Services Agency. Sidh is based on computer game hardware and software solutions but adds a novel interaction model and gameplay specifically developed for the purpose of training firefighters. The simulator environment is a cave where the player is interacting with the game through a set of sensors. Players move in the virtual world by movements in the physical world and a substantial physical effort is required to accomplish game tasks. Sidh has been used in a feasibility study where 31 firefighter students have been playing the game and the performance of these students as well as their reflections from using the game have been analyzed. Results from this study show that Sidh is a useful complement to traditional training methods and that the subjects give very high grades on the entertainment value of the game which indicate that this form of training may be self-motivating which is an important issue for voluntary, after-hours training.
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paper_title: Virtual reality used in a collaborative architectural design process

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This paper presents a project and considers the possibilities of using virtual reality in architectural design processes. The main goal of the project is to develop a process for collaborative design of laboratory layouts using VR (Cave-technology) as a tool integrated into the concepts of process architecture. The project has been carried out in co-operation with the Chemical Department at Lund Institute of Technology/Lund University. It is a "real" project integrated in the University's programming process. A workshop initiated the design process and was followed by a series of different design events, which were arranged with participants from one research and one education laboratory. At these events the participants made several visits to their future labs in a VR-Cave. The visits were alternated with more traditional design sessions using paper and pencil. The results show that the collaborative design process including VR helped users by providing a method with which their ideas could be better formulated, analyzed, tested, and finally realized. The results from the project have been incorporated into the building program for the new chemical laboratory building.
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paper_title: Perception and action

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The phrase perception and action is used widely but in diverse ways in the context of the relationship between perceptual and motor processes. This review describes and integrates five perspectives on perception and action which rely on both neurophysiological and behavioral levels of analysis. The two visual systems view proposes dissociable but interactive systems for conscious processing of objects/space and the visual control of action. The integrative view proposes tightly calibrated but flexible systems for perception and motor control in spatial representation. The embodied view posits that action underlies perception, involving common coding or motor simulation systems, and examines the relationship between action observation, imitation, and the understanding of intention. The ecological view emphasizes environmental information and affordances in perception. The functional view defines the relationship between perception, action planning, and semantics in goal-directed actions. Although some of these views/approaches differ in significant ways, their shared emphasis on the importance of action in perception serves as a useful unifying framework. WIREs Cogn Sci 2010 1 800–810 ::: ::: ::: ::: For further resources related to this article, please visit the WIREs website
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paper_title: Perceiving layout and knowing distances: The integration, relative potency, and contextual use of different information about depth

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Publisher Summary ::: This chapter discusses three questions: Why are there so many sources of information about layout? How is it that one perceives layout with near-metric accuracy when none of these sources yields metric information about it? Can one not do better, theoretically, in understanding the perception of layout than simply make a list? The answer to the first question begins with Todd's answer. Perceiving layout is extremely important to human beings, so important that it must be redundantly specified so that the redundancy can guard against the failure of any given source or the failure of any of the assumptions on which a given source is based. However, information redundancy is only part of the answer. Different sources of information about layout metrically reinforce and contrast with each other, providing a powerful network of constraints. The answer to the second proceeds from this idea. Through the analysis of depth-threshold functions for nine different sources of information about layout, one can begin to understand how those sources of information sharing the same-shaped functions across distances can help ramify judgments of layout by serving to correct measurement errors in each. Third, on the basis of the analyses and the pattern of functions, it suggests that list making has misled about space and layout. Psychologists and other vision scientists have generally considered layout, space, and distance as a uniform commodity in which observers carry out their day-to-day activities.
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paper_title: Terrain influences the accurate judgement of distance

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Mathematically, three-dimensional space can be represented differently by the cartesian, polar, and other coordinate systems. However, in physical sciences, the choice of representation system is restricted by the need to simplify a machine's computation while enhancing its efficiency1. Does the brain, for the same reasons, ‘select’ the most cost-efficient way to represent the three-dimensional location of objects? As we frequentlyinteract with objects on the common ground surface, it might be beneficial for the visual system to code an object's location using a ground-surface-based reference frame2. More precisely, the brain could use a quasi-two-dimensional coordinate system (x s, y s) with respect to the ground surface (s), rather than a strictly three-dimensional coordinate system (x, y, z), thus reducing coding redundancy and simplifying computations2,3,4,5. Here we provide support for this view by studying human psychophysical performance in perceiving absolute distance and in visually directed action tasks6,7,8,9,10,11. For example, when an object was seen on a continuous, homogeneous texture ground surface, the observer judged the distance to the object accurately. However, when similar surface information was unavailable, for example, when the object was seen across a gap in the ground, or across distinct texture regions, distance judgement was impaired.
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paper_title: Judging Egocentric Distance on the Ground: Occlusion and Surface Integration

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On the basis of the finding that a common and homogeneous ground surface is vital for accurate egocentric distance judgments (Sinai et al, 1998 Nature395 497–500), we propose a sequential-surface-integration-process (SSIP) hypothesis to elucidate how the visual system constructs a representation of the ground-surface in the intermediate distance range. According to the SSIP hypothesis, a near ground-surface representation is formed from near depth cues, and is utilized as an anchor to integrate the more distant surfaces by using texture-gradient information as the depth cue. The SSIP hypothesis provides an explanation for the finding that egocentric distance judgment is underestimated when a texture boundary exists on the ground surface that commonly supports the observer and target. We tested the prediction that the fidelity of the visually represented ground-surface reference frame depends on how the visual system selects the surface information for integration. Specifically, if information is selected ...
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paper_title: Depth Perception and the Perception of Events

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Three fundamental questions are addressed: (1) What are the effective sources of optical information for perceiving spatial relationships and events? Complex natural environments provide a plethora of information potentially related to spatial layout. Psychophysical research investigates the efficacy and perceptual processing of these potential cues to depth and events. (2) How is this information combined by the perceptual system? Viewed in isolation, individual cues typically do not fully specify the environmental properties to which they relate. In general, the rules for projecting three-dimensional layout onto the retina are unambiguously defined, whereas the inverse operation—from the image to the three-dimensional projected scene—is not. (3) Do people perceive space and events accurately? Certainly, people act in the environment as if they represent its spatial relationships accurately; however, effective action can often be achieved without geometrically correct representations. From a pragmatic perspective, perceptual representations are accurate to the degree that they provide effective guidance for behavior. This issue is developed and discussed throughout the chapter. ::: ::: ::: Keywords: ::: ::: binocular disparity; ::: depth cues; ::: ocular-motor depth cues; ::: optical flow; ::: perceptual organization; ::: perspective; ::: spatial layout
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paper_title: Foundations of Cyclopean Perception

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This classic work on cyclopean perception has influenced a generation of vision researchers, cognitive scientists, and neuroscientists and has inspired artists, designers, and computer graphics pioneers. In Foundations of Cyclopean Perception (first published in 1971 and unavailable for years), Bela Julesz traced the visual information flow in the brain, analyzing how the brain combines separate images received from the two eyes to produce depth perception. Julesz developed novel tools to do this: random-dot stereograms and cinematograms, generated by early digital computers at Bell Labs. These images, when viewed with the special glasses that came with the book, revealed complex, three-dimensional surfaces; this mode of visual stimulus became a paradigm for research in vision and perception. This reprint edition includes all 48 color random-dot designs from the original, as well as the special 3-D glasses required to view them.Foundations of Cyclopean Perception has had a profound impact on the vision studies community. It was chosen as one of the one hundred most influential works in cognitive science in a poll conducted by the University of Minnesota's Center for Cognitive Sciences. Many copies are "permanently borrowed" from college libraries; used copies are sought after online. Now, with this facsimile of the 1971 edition, the book is available again to cognitive scientists, neuroscientists, vision researchers, artists, and designers.
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paper_title: The importance of a visual horizon for distance judgments under severely degraded vision.

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In two experiments we examined the role of visual horizon information on absolute egocentric distance judgments to on-ground targets. Sedgwick [1983, in Human and Machine Vision (New York: Academic Press) pp 425–458] suggested that the visual system may utilize the angle of declination from a horizontal line of sight to the target location (horizon–distance relation) to determine absolute distances on infinite ground surfaces. While studies have supported this hypothesis, less is known about the specific cues (vestibular, visual) used to determine horizontal line of sight. We investigated this question by requiring observers to judge distances under degraded vision given an unaltered or raised visual horizon. The results suggest that visual horizon information does influence perception of absolute distances as evident through two different action-based measures: walking or throwing without vision to previously viewed targets. Distances were judged as shorter in the presence of a raised visual horizon. The...
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paper_title: Perceiving distance accurately by a directional process of integrating ground information

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By itself, the absolute distance of an object cannot be accurately judged beyond 2–3 m (refs 1–3). Yet, when it is viewed with reference to a flat terrain, humans accurately judge the absolute distance of the object up to 20 m, an ability that is important for various actions4,5,6,7,8. Here we provide evidence that this is accomplished by integrating local patches of ground information into a global surface reference frame. We first show that restricting an observer's visual field of view to the local ground area around the target leads to distance underestimation, indicating that a relatively wide expanse of the ground surface is required for accurate distance judgement. Second, as proof of surface integration, we show that even with the restricted view, the observer can accurately judge absolute distance by scanning local patches of the ground surface, bit by bit, from near to far, but not in the reverse direction. This finding also reveals that the surface integration process uses the near-ground-surface information as a foundation for surface representation, and extrapolation to the far ground surface around the target for accurate absolute distance computation.
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paper_title: Tool use affects perceived distance but only when you intend to use it

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Recent research demonstrates neurologic and behavioral differences in people’s responses to the space that is within and beyond reach. The present studies demonstrated a perceptual difference as well. Reachability was manipulated by having participants reach with and without a tool. Across 2 conditions, in which participants either held a tool or not, targets were presented at the same distances. Perceived distances to targets within reach holding the tool were compressed compared with targets that were beyond reach without it. These results suggest that reachability serves as a metric for perception. The 3rd experiment found that reachability only influenced perceived distance when the perceiver intended to reach. These experiments suggest that the authors perceive the environment in terms of our intentions and abilities to act within it.
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paper_title: Visual fatigue caused by viewing stereoscopic motion images: Background, theories, and observations

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The background, theories, and observations on visual stress possibly caused by viewing stereoscopic motion images are reviewed. Visual fatigue caused by stereoscopic images is a safety issue. Fatigue is possible caused by the discrepancy between accommodative and convergence stimuli that are included in the image. Studies on accommodation and convergence are surveyed and an explanation regarding the characteristics of these functions is offered. Studies in the literature on changes in oculomotor function after viewing stereoscopic images, including changes in pupillary responses, are discussed. Evaluation of visual fatigue, particularly in relation to different methods of viewing stereoscopic displays is described.
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paper_title: Follow Your Heart: Emotion Adaptively Influences Perception

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The current review introduces a new program of research that suggests the perception of spatial layout is influenced by emotions. Though perceptual systems are often described as closed and insulated, this review presents research suggesting that a variety of induced emotions (e.g., fear, disgust, sadness) can produce changes in vision and audition. Thus, the perceptual system may be highly interconnected, allowing emotional information to influence perceptions that, in turn, influence cognition. The body of work presented here also suggests that emotion-based changes in perception help us solve particular adaptive problems because emotion does not change all perceptions of the world. Taking the adaptive significance of emotion into account allows us to make predictions about when and how emotion influences perception.
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paper_title: Perception and action

paper_content:

The phrase perception and action is used widely but in diverse ways in the context of the relationship between perceptual and motor processes. This review describes and integrates five perspectives on perception and action which rely on both neurophysiological and behavioral levels of analysis. The two visual systems view proposes dissociable but interactive systems for conscious processing of objects/space and the visual control of action. The integrative view proposes tightly calibrated but flexible systems for perception and motor control in spatial representation. The embodied view posits that action underlies perception, involving common coding or motor simulation systems, and examines the relationship between action observation, imitation, and the understanding of intention. The ecological view emphasizes environmental information and affordances in perception. The functional view defines the relationship between perception, action planning, and semantics in goal-directed actions. Although some of these views/approaches differ in significant ways, their shared emphasis on the importance of action in perception serves as a useful unifying framework. WIREs Cogn Sci 2010 1 800–810 ::: ::: ::: ::: For further resources related to this article, please visit the WIREs website
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paper_title: Perceiving layout and knowing distances: The integration, relative potency, and contextual use of different information about depth

paper_content:

Publisher Summary ::: This chapter discusses three questions: Why are there so many sources of information about layout? How is it that one perceives layout with near-metric accuracy when none of these sources yields metric information about it? Can one not do better, theoretically, in understanding the perception of layout than simply make a list? The answer to the first question begins with Todd's answer. Perceiving layout is extremely important to human beings, so important that it must be redundantly specified so that the redundancy can guard against the failure of any given source or the failure of any of the assumptions on which a given source is based. However, information redundancy is only part of the answer. Different sources of information about layout metrically reinforce and contrast with each other, providing a powerful network of constraints. The answer to the second proceeds from this idea. Through the analysis of depth-threshold functions for nine different sources of information about layout, one can begin to understand how those sources of information sharing the same-shaped functions across distances can help ramify judgments of layout by serving to correct measurement errors in each. Third, on the basis of the analyses and the pattern of functions, it suggests that list making has misled about space and layout. Psychologists and other vision scientists have generally considered layout, space, and distance as a uniform commodity in which observers carry out their day-to-day activities.
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paper_title: Who is being deceived ? The experimental demands of wearing a backpack

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A growing literature argues that wearing a heavy backpack makes slopes look steeper and distances seem longer (e.g., Proffitt, 2006). To test for effects of experimental demand characteristics in a backpack experiment, we manipulated the experimental demand of the backpack and then used a postexperiment questionnaire to assess participants’ beliefs about the purpose of the backpack. For participants in the low-demand condition, an elaborate deception was used to provide an alternative explanation of the requirement to wear a heavy backpack (i.e., that it held EMG equipment). The highest slope judgments were found for those undeceived participants who guessed that the backpack was intended to affect their slope perception and also reported that they thought they were affected by it. When persuaded that the backpack served another purpose, participants’ slope estimates were no different from those of participants not wearing a backpack. These findings suggest that backpack effects, and other reported effects of effort on perception, are judgmental biases that result from the social, not physical, demands of the experimental context.
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paper_title: How does presentation method and measurement protocol affect distance estimation in real and virtual environments?

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We conducted two experiments that compared distance perception in real and virtual environments in six visual presentation methods using either timed imagined walking or direct blindfolded walking, while controlling for several other factors that could potentially impact distance perception. Our presentation conditions included unencumbered real world, real world seen through an HMD, virtual world seen through an HMD, augmented reality seen through an HMD, virtual world seen on multiple, large immersive screens, and photo-based presentation of the real world seen on multiple, large immersive screens. We found that there was a similar degree of underestimation of distance in the HMD and large-screen presentations of virtual environments. We also found that while wearing the HMD can cause some degree of distance underestimation, this effect depends on the measurement protocol used. Finally, we found that photo-based presentation did not help to improve distance perception in a large-screen immersive display system. The discussion focuses on points of similarity and difference with previous work on distance estimation in real and virtual environments.
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paper_title: Seeing beyond the target: Environmental context affects distance perception

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It is commonly assumed that perceived distance in full-cue, ecologically valid environments is redundantly specified and approximately veridical. However, recent research has called this assumption into question by demonstrating that distance perception varies in different types of environments even under full-cue viewing conditions. We report five experiments that demonstrate an effect of environmental context on perceived distance. We measured perceived distance in two types of environments (indoors and outdoors) with two types of measures (perceptual matching and blindwalking). We found effects of environmental context for both egocentric and exocentric distances. Across conditions, within individual experiments, all viewer-to-target depth-related variables were kept constant. The differences in perceived distance must therefore be explained by variations in the space beyond the target.
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paper_title: Visual Perception and the Guidance of Locomotion without Vision to Previously Seen Targets

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Two experiments were performed to assess the accuracy and precision with which adults perceive absolute egocentric distances to visible targets and coordinate their actions with them when walking without vision. In experiment 1 subjects stood in a large open field and attempted to judge the midpoint of self-to-target distances of between 4 and 24 m. In experiment 2 both highly practiced and unpracticed subjects stood in the same open field, viewed the same targets, and attempted to walk to them without vision or other environmental feedback under three conditions designed to assess the effects on accuracy of time-based memory decay and of walking at an unusually rapid pace. In experiment 1 the visual judgments were quite accurate and showed no systematic constant error. The small variable errors were linearly related to target distance. In experiment 2 the briskly paced walks were accurate, showing no systematic constant error, and the small, variable errors were a linear function of target distance and a...
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paper_title: Embodied perception with others’ bodies in mind: stereotype priming influence on the perception of spatial environment

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Abstract It has been shown that spatial perception is not only a function of optical variables but also a function of people’s physiological potential. When this potential is reduced, either due to age or fatigue, individuals have been observed to report hills steeper and distances longer. Two studies have demonstrated that the experience of an actual reduction in capacities is not necessary. After being primed with the elderly category, young participants estimated the gradient of various pathways and that of a hill steeper (Study 1) and distances across a grassy field longer (Study 2) than their non-primed counterparts. The activation of a social category has often been found to result in stereotype-congruent behaviors. The present findings indicate that, in addition to this well-documented behavioral mimetism, this activation also leads to perceptual mimetism. I suggest that it helps facilitate social interactions by investing the partners with a shared vision of their environment.
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paper_title: Minification and gap affordances in head-mounted displays

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Numerous studies report that people underestimate egocentric distances in head-mounted display (HMD) virtual environments compared to real environments when measured with direct blind walking. Recently, Zhang et al. [2012] demonstrated that minification can make verbal reports and blind walking more consistent with similar real world judgments. This research examines if minification causes people to misjudge gap affordances. We found that minification did not affect participants' verbal reports of whether they could fit through a gap without turning their shoulders.
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paper_title: Environmental context influences visually perceived distance

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What properties determine visually perceived space? We discovered that the perceived relative distances of familiar objects in natural settings depended in unexpected ways on the surrounding visual field. Observers bisected egocentric distances in a lobby, in a hallway, and on an open lawn. Three key findings were the following: (1) Perceived midpoints were too far from the observer, which is the opposite of the common foreshortening effect. (2) Thisantiforeshortening constant error depended on the environmental setting — greatest in the lobby and hall but nonsignificant on the lawn. (3) Context also affected distance discrimination; variability was greater in the hall than in the lobby or on the lawn. A second experiment replicated these findings, using a method of constant stimuli. Evidently, both the accuracy and the precision of perceived distance depend on subtle properties of the surrounding environment.
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paper_title: Perceiving distance: A role of effort and intent

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Perceiving egocentric distance is not only a function of the optical variables to which it relates, but also a function of people's current physiological potential to perform intended actions. In a set of experiments, we showed that, as the effort associated with walking increases, perceived distance increases if the perceiver intends to walk the extent, but not if the perceiver intends to throw. Conversely, as the effort associated with throwing increases, perceived distance increases if people intend to throw to the target, but not if they intend to walk. Perceiving distance combines the geometry of the world with our behavior goals and the potential of our body to achieve these goals.
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paper_title: Wishful Seeing More Desired Objects Are Seen as Closer

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Although people assume that they see the surrounding environment as it truly is, we suggest that perception of the natural environment is dependent upon the internal goal states of perceivers. Five experiments demonstrated that perceivers tend to see desirable objects (i.e., those that can fulfill immediate goals—a water bottle to assuage their thirst, money they can win, a personality test providing favorable feedback) as physically closer to them than less desirable objects. Biased distance perception was revealed through verbal reports and through actions toward the object (e.g., underthrowing a beanbag at a desirable object). We suggest that seeing desirable objects as closer than less desirable objects serves the self-regulatory function of energizing the perceiver to approach objects that fulfill needs and goals.
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paper_title: Comparison of Two Indicators of Perceived Egocentric Distance Under Full-Cue and Reduced-Cue Conditions

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It has not been established that walking without vision to previewed targets is indeed controlled by perceived distance. To this end, we compared walking and verbal report as distance indicators, looking for a tight covariation in responses that would indicate control by a common variable. Targets from 79-500 cm away were presented under dark and well-lit conditions. Both verbal reports and walking indicated overestimation of near targets and underestimation of far targets under dark viewing conditions. Moreover, the finding that verbally reported distance plotted essentially as a single-valued function of walked distance and vice versa is evidence that both indicators were responding to the same internal variable, ostensibly perceived distance. In addition, binocular parallax, absolute motion parallax, and angular elevation were evaluated as distance cues, and only angular elevation exerted a large influence on perceived distance. When people are asked to view an object in a well-lit environment and then attempt to walk over to it with eyes closed, they do so, on average, without large systematic error. This finding has been documented by several researchers (Corlett, Patla, & Williams, 1985; Elliott, 1986,
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paper_title: Distance perception in real and virtual environments

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Two experiments were conducted to compare distance perception in real and virtual environments. In Experiment 1, adults estimated how long it would take to walk to targets in real and virtual environments by starting and stopping a stopwatch while looking at a target person standing between 20 and 120 ft away. The real environment was a large grassy lawn in front of a university building. We replicated this scene in our virtual environment using a nonstereoscopic, large screen immersive display system. We found that people underestimated time to walk in both environments for distances of 40--60 ft and beyond. However, time-to-walk estimates were virtually identical across the two environments. In Experiment 2, 10- and 12-year-old children and adults estimated time to walk in real and virtual environments both with and without vision. Adults again underestimated time to walk in both environments for distances of 60 ft and beyond. Again, their estimates were virtually identical in the real and virtual environment both with and without vision. Children's time-to-walk estimates were also very similar across the two environments under both viewing conditions. We conclude that distance perception may be better in virtual environments involving large screen immersive displays than those involving head mounted displays (HMDs).
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paper_title: Can I pass?: using affordances to measure perceived size in virtual environments

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Perception of an accurate sense of the scale depicted in computer graphics is important for many applications. How to best characterize the accuracy of space perception in computer graphics is a question that does not have a simple answer. This paper describes the use of perceived affordances as a way of measuring the perceptual fidelity of virtual environments with respect to how well they convey information about geometric scale. The methodology involves a verbal indication that a particular action can or cannot be performed in a viewed environment. By varying the spatial structure of the environment, these affordance judgments can be used to probe how accurately viewers are able to perceive action-relevant spatial information. The result is a measure relevant to action, less subject to bias than verbal reports of more primitive properties such as size or distance, and applicable to non-virtual-environment display systems in which the actual action cannot be performed. We demonstrate the approach in an experiment comparing one type of affordance judgment, perceived passability, with judgments of size and distance in matched real world and virtual world environments.
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paper_title: Perceptual issues in augmented reality revisited

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This paper provides a classification of perceptual issues in augmented reality, created with a visual processing and interpretation pipeline in mind. We organize issues into ones related to the environment, capturing, augmentation, display, and individual user differences. We also illuminate issues associated with more recent platforms such as handhelds or projector-camera systems. Throughout, we describe current approaches to addressing these problems, and suggest directions for future research.
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paper_title: Egocentric depth judgments in optical, see-through augmented reality

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A fundamental problem in optical, see-through augmented reality (AR) is characterizing how it affects the perception of spatial layout and depth. This problem is important because AR system developers need to both place graphics in arbitrary spatial relationships with real-world objects, and to know that users will perceive them in the same relationships. Furthermore, AR makes possible enhanced perceptual techniques that have no real-world equivalent, such as x-ray vision, where AR users are supposed to perceive graphics as being located behind opaque surfaces. This paper reviews and discusses protocols for measuring egocentric depth judgments in both virtual and augmented environments, and discusses the well-known problem of depth underestimation in virtual environments. It then describes two experiments that measured egocentric depth judgments in AR. Experiment I used a perceptual matching protocol to measure AR depth judgments at medium and far-field distances of 5 to 45 meters. The experiment studied the effects of upper versus lower visual field location, the x-ray vision condition, and practice on the task. The experimental findings include evidence for a switch in bias, from underestimating to overestimating the distance of AR-presented graphics, at ~ 23 meters, as well as a quantification of how much more difficult the x-ray vision condition makes the task. Experiment II used blind walking and verbal report protocols to measure AR depth judgments at distances of 3 to 7 meters. The experiment examined real-world objects, real-world objects seen through the AR display, virtual objects, and combined real and virtual objects. The results give evidence that the egocentric depth of AR objects is underestimated at these distances, but to a lesser degree than has previously been found for most virtual reality environments. The results are consistent with previous studies that have implicated a restricted field-of-view, combined with an inability for observers to scan the ground plane in a near-to-far direction, as explanations for the observed depth underestimation.
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paper_title: Oculomotor changes within virtual environments

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Abstract This paper discusses the oculomotor changes which might be expected to occur during immersion in a virtual environment whilst wearing a Head mounted display (HMD). To do so, it first examines the stimulus presented to the eyes, and then considers how this stimulus could affect the visual system. Theoretical analysis and empirical results from the use of three different HMDs point towards the same conclusion, that in this context a mismatch between the instrument inter-ocular distance (IOD) and the user’s inter-pupillary distance is of little concern, unlike the mismatch between the instrument IOD and the inter-screen distance.
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paper_title: Spatial distortion prediction system for stereoscopic images

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We propose a system to calculate the spatial distortion in 3-D images based on the shooting, display, and viewing conditions. It can be used to predict the extent of the perceived puppet-theater effect and the cardboard effect. The magnitude of the spatial distor- tion and the extent of the puppet-theater and cardboard effects are displayed using a space grid whose size can be estimated based on the objects' depths, calculated from the binocular parallax of the acquired stereoscopic images. This system can also be used to predict excessive binocular parallax and excessive parallax distribu- tion. Several cases in which puppet-theater and cardboard effects are expected to be produced are presented. We also demonstrate how the proposed system might be used to predict ratings of natu- ralness and quality of depth. © 2006 SPIE and
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paper_title: Accommodation and Size-Constancy of Virtual Objects

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Accommodation has been suspected as a contributor to size illusions in virtual environments (VE) due to the lack of appropriate accommodative stimuli in a VE for the objects displayed. Previous experiments examining size-constancy in VE have shown that monocular cues to depth that accompany the object are a major contributor to correct size perception. When these accompanying cues are removed perceived size varied with the object's distance from the subject, i.e., visual angle. If accommodation were the dominant mechanism contributing to a visual angle response [due to its action to keep physical objects clear] in this condition, an open-loop accommodation viewing condition might restore size-constancy to this condition. Pinhole apertures were used to open-loop accommodation and examine if size-constancy might be restored when few accompanying monocular cues to depth were present. Visual angle performance when viewing a low cue environment was found with and without the use of the pinhole apertures. Thus, these results signify that accommodation does not play a dominate role in the loss of size-constancy in sparse visual environments often used in VE. These results suggest that size-constancy is driven by the inclusion of the remaining monocular cues to depth in VE as it is in the physical world.
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paper_title: Balancing fusion, image depth and distortion in stereoscopic head-tracked displays

paper_content:

Abstract Stereoscopic display is a fundamental part of virtual reality HMDsystems and HTD (head-tracked display) systems such as thevirtual workbench and the CAVE. A common practice instereoscopic systems is deliberate incorrect modeling of user eyeseparation. Underestimating eye separation is frequentlynecessary for the human visual system to fuse stereo image pairsinto single 3D images, while overestimating eye separationenhances image depth. Unfortunately, false eye separationmodeling also distorts the perceived 3D image in undesirableways. This paper makes three fundamental contributions tounderstanding and controlling this stereo distortion. (1) Weanalyze the distortion using a new analytic description. Thisanalysis shows that even with perfect head tracking, a user willperceive virtual objects to warp and shift as she moves her head.(2) We present a new technique for counteracting the shearingcomponent of the distortion. (3) We present improved methodsfor managing image fusion problems for distant objects and forenhancing the depth of flat scenes.CR Categories and Subject Descriptions: I.3.7 [ComputerGraphics] Three-Dimensional Graphics and Realism - VirtualReality; I.3.6 [Computer Graphics] Methodology and Techniques– Ergonomics; I.3.6 [Computer Graphics] Methodology andTechniques – Interaction Techniques; I.3.3 [Computer Graphics]Picture/Image Generation – Viewing AlgorithmsAdditional Keywords: virtual reality, stereoscopic display,head-tracking, image distortion
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paper_title: Virtual Audio Systems

paper_content:

To be immersed in a virtual environment, the user must be presented with plausible sensory input including auditory cues. A virtual (three-dimensional) audio display aims to allow the user to perceive the position of a sound source at an arbitrary position in three-dimensional space despite the fact that the generated sound may be emanating from a fixed number of loudspeakers at fixed positions in space or a pair of headphones. The foundation of virtual audio rests on the development of technology to present auditory signals to the listener's ears so that these signals are perceptually equivalent to those the listener would receive in the environment being simulated. This paper reviews the human perceptual and technical literature relevant to the modeling and generation of accurate audio displays for virtual environments. Approaches to acoustical environment simulation are summarized and the advantages and disadvantages of the various approaches are presented.
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paper_title: Auditory distance perception in humans : A summary of past and present research

paper_content:

Although auditory distance perception is a critical component of spatial hearing, it has received substantially less scienti.c attention than the directional aspects of auditory localization. Here we summarize current knowledge on auditory distance perception, with special emphasis on recent research results. The summary will be structured around three central questions. 1. How accurately can humans estimate the distances of stationary sound sources? We show that this psychophysical relationship is well approximated by a compressive power function, which suggests that listeners systematically underestimate distances to faraway sound sources. 2. What determines perceived sound source distance? We examine the various acoustical and non-acoustical factors thought to contribute to source distance percepts, and summarize the psychophysical literature relevant to each factor. 3. What are the neural correlates to perceived sound source distance? Recent evidence points to the role of areas within right temporal cortex in auditory distance perception, as well as in other spatial tasks in different sensory modalities.
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paper_title: Accommodation, occlusion, and disparity matching are used to guide reaching: a comparison of actual versus virtual environments.

paper_content:

The authors used a virtual environment to investigate visual control of reaching and monocular and binocular perception of egocentric distance, size, and shape. With binocular vision, the results suggested use of disparity matching. This was tested and confirmed in the virtual environment by eliminating other information about contact of hand and target. Elimination of occlusion of hand by target destabilized monocular but not binocular performance. Because the virtual environment entails accommodation of an image beyond reach, the authors predicted overestimation of egocentric distances in the virtual relative to actual environment. This was confirmed. The authors used -2 diopter glasses to reduce the focal distance in the virtual environment. Overestimates were reduced by half. The authors conclude that calibration of perception is required for accurate feedforward reaching and that disparity matching is optimal visual information for calibration.
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paper_title: The underestimation of egocentric distance: evidence from frontal matching tasks

paper_content:

There is controversy over the existence, nature, and cause of error in egocentric distance judgments. One proposal is that the systematic biases often found in explicit judgments of egocentric distance along the ground may be related to recently observed biases in the perceived declination of gaze (Durgin & Li, Attention, Perception, & Psychophysics, in press), To measure perceived egocentric distance nonverbally, observers in a field were asked to position themselves so that their distance from one of two experimenters was equal to the frontal distance between the experimenters. Observers placed themselves too far away, consistent with egocentric distance underestimation. A similar experiment was conducted with vertical frontal extents. Both experiments were replicated in panoramic virtual reality. Perceived egocentric distance was quantitatively consistent with angular bias in perceived gaze declination (1.5 gain). Finally, an exocentric distance-matching task was contrasted with a variant of the egocentric matching task. The egocentric matching data approximate a constant compression of perceived egocentric distance with a power function exponent of nearly 1; exocentric matches had an exponent of about 0.67. The divergent pattern between egocentric and exocentric matches suggests that they depend on different visual cues.
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paper_title: Revisiting the effect of quality of graphics on distance judgments in virtual environments: A comparison of verbal reports and blind walking

paper_content:

In immersive virtual environments, judgments of perceived egocentric distance are significantly underestimated, as compared with accurate performance in the real world. Two experiments assessed the influence of graphics quality on two distinct estimates of distance, a visually directed walking task and verbal reports. Experiment 1 demonstrated a similar underestimation of distances walked to previously viewed targets in both low- and high-quality virtual classrooms. In Experiment 2, participants’ verbal judgments underestimated target distances in both graphics quality environments but were more accurate in the high-quality environment, consistent with the subjective impression that high-quality environments seem larger. Contrary to previous results, we suggest that quality of graphics does influence judgments of distance, but only for verbal reports. This behavioral dissociation has implications beyond the context of virtual environments and may reflect a differential use of cues and context for verbal reports and visually directed walking.
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paper_title: The influence of restricted viewing conditions on egocentric distance perception: Implications for real and virtual environments

paper_content:

We carried out three experiments to examine the influence of field of view and binocular viewing restrictions on absolute distance perception in real-world indoor environments. Few of the classical visual cues provide direct information for accurate absolute distance judgments to points in the environment beyond about 2 m from the viewer. Nevertheless, in previous work it has been found that visually directed walking tasks reveal accurate distance estimations in full-cue real-world environments to distances up to 20 m. In contrast, the same tasks in virtual environments produced with head-mounted displays (HMDs) show large compression of distance. Field of view and binocular viewing are common limitations in research with HMDs, and have been rarely studied under full pictorial-cue conditions in the context of distance perception in the real-world. Experiment 1 showed that the view of one's body and feet on the floor was not necessary for accurate distance perception. In experiment 2 we manipulated the hor...
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paper_title: The influence of feedback on egocentric distance judgments in real and virtual environments

paper_content:

A number of investigators have reported that distance judgments in virtual environments (VEs) are systematically smaller than distance judgments made in comparably-sized real environments. Many variables that may contribute to this difference have been investigated but none of them fully explain the distance compression. One approach to this problem that has implications for both VE applications and the study of perceptual mechanisms is to examine the influence of the feedback available to the user. Most generally, we asked whether feedback within a virtual environment would lead to more accurate estimations of distance. Next, given the prediction that some change in behavior would be observed, we asked whether specific adaptation effects would generalize to other indications of distance. Finally, we asked whether these effects would transfer from the VE to the real world. All distance judgments in the head-mounted display (HMD) became near accurate after three different forms of feedback were given within the HMD. However, not all feedback sessions within the HMD altered real world distance judgments. These results are discussed with respect to the perceptual and cognitive mechanisms that may be involved in the observed adaptation effects as well as the benefits of feedback for VE applications.
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paper_title: Interaction with an immersive virtual environment corrects users' distance estimates.

paper_content:

OBJECTIVE ::: Two experiments examined whether prior interaction within an immersive virtual environment (VE) enabled people to improve the accuracy of their distance judgments and whether an improved ability to estimate distance generalized to other means of estimating distances. ::: ::: ::: BACKGROUND ::: Prior literature has consistently found that users of immersive VEs underestimate distances by approximately 50%. ::: ::: ::: METHOD ::: In each of the two experiments, 16 participants viewed objects in an immersive VE and estimated their distance to them by means of blindfolded walking tasks before and after interacting with the VE. ::: ::: ::: RESULTS ::: The interaction task significantly corrected users' underestimation bias to nearly veridical. Differences between pre- and post-interaction mean distance estimation accuracy were large (d = 4.63), and significant (p < .001), and they generalized across response task. ::: ::: ::: CONCLUSION ::: This finding limits the generality of the underestimation effect in VEs and suggests that distance underestimation in VEs may not be a road block to the development of VE applications. ::: ::: ::: APPLICATION ::: Potential or actual applications of this research include the improvement of VE systems requiring accurate spatial awareness.
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paper_title: How does presentation method and measurement protocol affect distance estimation in real and virtual environments?

paper_content:

We conducted two experiments that compared distance perception in real and virtual environments in six visual presentation methods using either timed imagined walking or direct blindfolded walking, while controlling for several other factors that could potentially impact distance perception. Our presentation conditions included unencumbered real world, real world seen through an HMD, virtual world seen through an HMD, augmented reality seen through an HMD, virtual world seen on multiple, large immersive screens, and photo-based presentation of the real world seen on multiple, large immersive screens. We found that there was a similar degree of underestimation of distance in the HMD and large-screen presentations of virtual environments. We also found that while wearing the HMD can cause some degree of distance underestimation, this effect depends on the measurement protocol used. Finally, we found that photo-based presentation did not help to improve distance perception in a large-screen immersive display system. The discussion focuses on points of similarity and difference with previous work on distance estimation in real and virtual environments.
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paper_title: Locomotor and verbal distance judgments in action and vista space

paper_content:

Judging distances is crucial when interacting with the environment. For short distances in action space (up to 30 m), both explicit verbal estimates and locomotor judgments are fairly accurate. For large distances, data have remained scarce. In two laboratory experiments, our observers judged distances to visual targets presented stereoscopically, either by giving a verbal estimate or by walking the distance to the target on a treadmill. While verbal judgments remained linearly scaled over the whole range of distances from 20 to 262 m, locomotor judgments fell short at distances above 100 m, indicating that observers overestimated the distance they had traveled and increasingly did so as a function of actual target distance. This pattern persisted when controlling for the potential confound of fatigue or reluctance to walk. We discuss different approaches to explain our findings and stress the importance of a differential use of distance cues. A model of leaky path integration showed a good fit with our locomotor data.
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paper_title: Perceived egocentric distances in real, image-based, and traditional virtual environments

paper_content:

In virtual environments, perceived egocentric distances are consistently underestimated when compared to the same distance judgments in the real world. The research presented in this paper explores two possible causes for the compressed distance perception in virtual environments: (1) real-time computer graphics rendering, and (2) immersive display technology. Our results show there is a significant difference in distance judgments between real and virtual environments. However, the differences between distance judgments in virtual photographic panorama environments and traditionally rendered virtual environments are small, suggesting that the display device is affecting distance judgments in virtual environments.
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paper_title: The effects of head-mounted display mechanical properties and field of view on distance judgments in virtual environments

paper_content:

Research has shown that people are able to judge distances accurately in full-cue, real-world environments using visually directed actions. However, in virtual environments viewed with head-mounted display (HMD) systems, there is evidence that people act as though the virtual space is smaller than intended. This is a surprising result given how well people act in real environments. The behavior in the virtual setting may be linked to distortions in the available visual cues or to a person's ability to locomote without vision. Either could result from issues related to added mass, moments of inertia, and restricted field of view in HMDs. This article describes an experiment in which distance judgments based on normal real-world and HMD viewing are compared with judgments based on real-world viewing while wearing two specialized devices. One is a mock HMD, which replicated the mass, moments of inertia, and field of view of the HMD and the other an inertial headband designed to replicate the mass and moments of inertia of the HMD, but constructed to not restrict the field of view of the observer or otherwise feel like wearing a helmet. Distance judgments using the mock HMD showed a statistically significant underestimation relative to the no restriction condition but not of a magnitude sufficient to account for all the distance compression seen in the HMD. Indicated distances with the inertial headband were not significantly smaller than those made with no restrictions.
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paper_title: Estimating Distance in Real and Virtual Environments: Does Order Make a Difference?

paper_content:

In this investigation, we examined how the order in which people experience real and virtual environments influences their distance estimates. Participants made two sets of distance estimates in one of the following conditions: (1) real environment first, virtual environment second; (2) virtual environment first, real environment second; (3) real environment first, real environment second; or (4) virtual environment first, virtual environment second. In Experiment 1, the participants imagined how long it would take to walk to targets in real and virtual environments. The participants’ first estimates were significantly more accurate in the real than in the virtual environment. When the second environment was the same as the first environment (real-real and virtual-virtual), the participants’ second estimates were also more accurate in the real than in the virtual environment. When the second environment differed from the first environment (real-virtual and virtual-real), however, the participants’ second estimates did not differ significantly across the two environments. A second experiment, in which the participants walked blindfolded to targets in the real environment and imagined how long it would take to walk to targets in the virtual environment, replicated these results. These subtle yet persistent order effects suggest that memory can play an important role in distance perception.
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paper_title: The effects of virtual character animation on spatial judgments

paper_content:

Inaccurate perception of distances is a known problem within virtual environments. We hypothesize that the inclusion of virtual characters within these environments can improve an observer's ability to judge distances and achieve accurate spatial understanding. We have conducted an empirical study using a desktop display of a small scale environment to evaluate the validity of this concept. We investigated whether the presence and quantity of virtual human characters, as well as the naturalness of their locomotion animations, could improve egocentric and exocentric distance estimations. Preliminary results suggest that static or properly animated characters could improve exocentric estimations, and properly animated characters could reduce egocentric distance compression errors.
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paper_title: Egocentric Distance Perception in a Virtual Environment Using a Perceptual Matching Task

paper_content:

Objective: To determine whether egocentric distance judgments are accurate in a virtual environment using a perceptual matching task. Methods: Observers were immersed within a virtual environment consisting of an L-shaped room with a test object (a column) located down one corridor and a comparison object (a flagpole) located down the other. Perceived distances were measured by having the observers move the comparison object to match the distance to the test object. Textures in each corridor were independently varied, as was the size of the test object. Results: Significant effects were found for the texture pattern under the test object and for distance, but not for the texture under the comparison object or column size. Performance was best with a regular (brick) pattern. Overall, observers' judgments overestimated distance to the test object by approximately 7%. Conclusions: Egocentric distance judgments were relatively accurate compared to past research. Texture affected performance, with a regular pa...
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paper_title: Egocentric distance perception in real and HMD-based virtual environments: the effect of limited scanning method

paper_content:

We conducted four experiments on egocentric depth perception using blind walking with a restricted scanning method in both the real and a virtual environment. Our viewing condition in all experiments was monocular. We varied the field of view (real), scan direction (real), blind walking method (real and virtual), and self-representation (virtual) over distances of 4 meters to 7 meters. The field of view varied between 21.1° and 13.6°. The scan direction varied between near-to-far scanning and far-to-near scanning. The blind walking method varied between direct blind walking and an indirect method of blind walking that matched the geometry of our laboratory. We varied self-representation between having a self-avatar (a fully tracked, animated, and first-person perspective of the user), having a static avatar (a mannequin avatar that did not move), to having no avatar (a disembodied camera view of the virtual environment). In the real environment, we find an effect of field of view; participants performed more accurately with larger field of view. In both real and virtual environments, we find an effect of blind walking method; participants performed more accurately in direct blind walking. We do not find an effect of distance underestimation in any environment, nor do we find an effect of self-representation.
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paper_title: Effect of Viewing Plane on Perceived Distances in Real and Virtual Environments

paper_content:

Three experiments examined perceived absolute distance in a head-mounted display virtual environment (HMD-VE) and a matched real-world environment, as a function of the type and orientation of the distance viewed. In Experiment 1, participants turned and walked, without vision, a distance to match the viewed interval for both egocentric (viewer-to-target) and exocentric (target-to-target) extents. Egocentric distances were underestimated in the HMD-VE while exocentric distances were estimated similarly across environments. Since egocentric distances were displayed in the depth plane and exocentric distances in the frontal plane, the pattern of results could have been related to the orientation of the distance or to the type of distance. Experiments 2 and 3 tested these alternatives. Participants estimated exocentric distances presented along the depth or frontal plane either by turning and walking (Experiment 2) or by turning and throwing a beanbag to indicate the perceived extent (Experiment 3). For both Experiments 2 and 3, depth intervals were underestimated in the HMD-VE compared to the real world. However, frontal intervals were estimated similarly across environments. The findings suggest anisotropy in HMD-VE distance perception such that distance underestimation in the HMD-VE generalizes to intervals in the depth plane, but not to intervals in the frontal plane.
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paper_title: Analyzing effects of geometric rendering parameters on size and distance estimation in on-axis stereographics

paper_content:

Accurate perception of size and distance in a three-dimensional virtual environment is important for many applications. However, several experiments have revealed that spatial perception of virtual environments often deviates from the real world, even when the virtual scene is modeled as an accurate replica of a familiar physical environment. While previous research has elucidated various factors that can facilitate perceptual shifts, the effects of geometric rendering parameters on spatial cues are still not well understood. In this paper, we model and evaluate effects of spatial transformations caused by variations of the geometric field of view and the interpupillary distance in on-axis stereographic display environments. We evaluated different predictions in a psychophysical experiment in which subjects were asked to judge distance and size properties of virtual objects placed in a realistic virtual scene. Our results suggest that variations in the geometric field of view have a strong influence on distance judgments, whereas variations in the geometric interpupillary distance mainly affect size judgments.
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paper_title: Distance estimation in virtual and real environments using bisection

paper_content:

Systematic error in judging distances in virtual environments is one of the most interesting problems in perceptual studies of virtual environments. The causes of this error are not known. This paper presents an experiment designed to investigate distance perception in virtual environments using the method of distance bisection (fractionation). Most other studies of distance perception in virtual environment rely on measures involving motor responses or time judgments. Unlike these, the method used in this study depends purely on visually perceived distances. Our experiment compares distance bisection judgments in virtual environments, bisection judgments in the real-world, and bisection judgments in the real-world with limited field of view. We also perform the judgments in two environmental contexts, an outdoor environment and an indoor environment. We find evidence that nonlinear distance compression occurs in virtual environments, but judgments in real-world conditions are accurate. We do not find an effect of environmental context.
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paper_title: Size-Constancy in the CAVE

paper_content:

The use of virtual environments (VE) for many research and commercial purposes relies on its ability to generate environments that faithfully reproduce the physical world. However, due to its limitations the VE can have a number of flaws that adversely affect its use and believability. One of the more important aspects of this problem is whether the size of an object in the VE is perceived as it would be in the physical world. One of the fundamental phenomena for correct size is size-constancy, that is, an object is perceived to be the same size regardless of its distance from the observer. This is in spite of the fact that the retinal size of the object shrinks with increasing distance from the observer. We examined size-constancy in the CAVE and found that size-constancy is a strong and dominant perception in our subject population when the test object is accompanied by surrounding environmental objects. Furthermore, size-constancy changes to a visual angle performance (i.e., object size changed with distance from the subject) when these surrounding objects are removed from the scene. As previously described for the physical world, our results suggest that it is necessary to provide surrounding objects to aid in the determination of an object's depth and to elicit size-constancy in VE. These results are discussed regarding their implications for viewing objects in projection-based VE and the environments that play a role in the perception of object size in the CAVE.
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paper_title: Virtual reality system effects on size-distance judgements in a virtual environment

paper_content:

The paper provides an assessment of how selected properties of a virtual reality system impact size-distance judgments in a virtual environment. Manipulations are made in viewing conditions (biocular vs. stereoscopic), image resolution, field of view, scene contrast and target distance, while subjects attempt to match the attributes of a comparison object with a standard object. General findings suggest that under more natural viewing conditions, size-distance judgements in virtual environments differ from those found previously in physical environments whereas, under impoverished conditions, performance differences between the two environments are similar.
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paper_title: Does the Quality of the Computer Graphics Matter when Judging Distances in Visually Immersive Environments?

paper_content:

In the real world, people are quite accurate in judging distances to locations in the environment, at least for targets resting on the ground plane and distances out to about 20m. Distance judgments in visually immersive environments are much less accurate. Several studies have now shown that in visually immersive environments, the world appears significantly smaller than intended, This study investigates whether or not the compression in apparent distances is the result of the low-quality computer graphics utilized in previous investigations, Visually directed triangulated walking was used to assess distance judgments in the real world and in three virtual environments with graphical renderings of varying quality.
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paper_title: Audio , visual , and audio-visual egocentric distance perception in virtual environments

paper_content:

Previous studies have shown that in real environments, distances are visually correctly estimated. In visual (V) virtual environments (VEs), distances are systematically underestimated. In audio (A) real and virtual environments, near distances ( 2 m) are underestimated. However, little is known regarding combined A and V interactions on the egocentric distance perception in VEs. In this paper we present a study of A, V, and AV egocentric distance perception in VEs. AV rendering is provided via the SMART-I2 platform using tracked passive visual stereoscopy and acoustical wave field synthesis (WFS). Distances are estimated using triangulated blind walking under A, V, and AV conditions. Distance compressions similar to those found in previous studies are observed under each rendering condition. The audio and visual modalities appears to be of similar precision for distance estimations in virtual environments. This casts doubts on the commonly accepted visual capture theory in distance perception.
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paper_title: Throwing versus walking as indicators of distance perception in similar real and virtual environments

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For humans to effectively interact with their environment, it is important for the visual system to determine the absolute size and distance of objects. Previous experiments performed in full-cue, real-world environments have demonstrated that blind walking to targets serves as an accurate indication of distance perception, up to about 25 m. In contrast, the same task performed in virtual environments (VEs) using head-mounted displays shows significant underestimation in walking. To date, blind walking is the only visually directed action task that has been used to evaluate distance perception in VEs beyond reaching distances. The possible influence of the response measure itself on absolute distance perception in virtual environments is currently an open question. Blind walking involves locomotion and the egocentric updating of the environment with one's own movement. We compared this measure to blind throwing, a task that involves the initiation of a movement directed by vision, but no further interaction within the environment. Both throwing and walking were compressed in the VE but accurate in the real world. We suggest that distance compression found in VEs may be a result of a general perceptual origin rather than specific to the response measure.
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paper_title: Distance perception in real and virtual environments

paper_content:

Two experiments were conducted to compare distance perception in real and virtual environments. In Experiment 1, adults estimated how long it would take to walk to targets in real and virtual environments by starting and stopping a stopwatch while looking at a target person standing between 20 and 120 ft away. The real environment was a large grassy lawn in front of a university building. We replicated this scene in our virtual environment using a nonstereoscopic, large screen immersive display system. We found that people underestimated time to walk in both environments for distances of 40--60 ft and beyond. However, time-to-walk estimates were virtually identical across the two environments. In Experiment 2, 10- and 12-year-old children and adults estimated time to walk in real and virtual environments both with and without vision. Adults again underestimated time to walk in both environments for distances of 60 ft and beyond. Again, their estimates were virtually identical in the real and virtual environment both with and without vision. Children's time-to-walk estimates were also very similar across the two environments under both viewing conditions. We conclude that distance perception may be better in virtual environments involving large screen immersive displays than those involving head mounted displays (HMDs).
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paper_title: Egocentric distance judgments in a large screen display immersive virtual environment

paper_content:

People underestimate egocentric distances in head-mounted display virtual environments, as compared to estimates done in the real world. Our work investigates whether distances are still compressed in a large screen display immersive virtual environment, where participants are able to see their own body surrounded by the virtual environment. We conducted our experiment in both the real world using a real room and the large screen display immersive virtual environment using a 3D model of the real room. Our results showed a significant underestimation of verbal reports of egocentric distances in the large screen display immersive virtual environment, while the distance judgments of the real world were closer to veridical. Moreover, we observed a significant effect of distances in both environments. In the real world closer distances were slightly underestimated, while further distances were slightly overestimated. In contrast to the real world in the virtual environment participants overestimated closer distances (up to 2.5m) and underestimated distances that were further than 3m. A possible reason for this effect of distances in the virtual environment may be that participants perceived stereo cues differently when the target was projected on the floor versus on the front of the large screen.
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paper_title: Near-field distance perception in real and virtual environments using both verbal and action responses

paper_content:

Few experiments have been performed to investigate near-field egocentric distance estimation in an Immersive Virtual Environment (IVE) as compared to the Real World (RW). This article investigates near-field distance estimation in IVEs and RW conditions using physical reach and verbal report measures, by using an apparatus similar to that used by Bingham and Pagano [1998]. Analysis of our experiment shows distance compression in both the IVE and RW conditions in participants' perceptual judgments to targets. This is consistent with previous research in both action space in an IVE and reach space with Augmented Reality (AR). Analysis of verbal responses from participants revealed that participants underestimated significantly less in the virtual world as compared to the RW. We also found that verbal reports and reaches provided different results in both IVEs and RW environments.
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paper_title: Nonvisually Guided Locomotion to a Previously Viewed Target in Real and Virtual Environments

paper_content:

Comparing human performance in a virtual environment (VE) with performance in the real world can provide clues about which aspects of VE technology require improvement. Using a technique previously shown to measure real-world distance judgments accurately, we compared performance in a real-world environment with performance in a virtual model of that environment. The technique required participants to walk without vision to a target after viewing it for 10 s. VE distance judgments averaged 85% of the target distance, whereas real-world judgments averaged 92%. The magnitude of the relative errors in the VE was twice that in the real world, indicating that the VE degraded distance judgments. Our analysis suggests that VE performance deficits result either from poor binocular disparity cues or from distortion of pictorial depth cues. Actual or potential applications of this research include the development of virtual environments for training and the design of visual displays for virtual simulations.
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paper_title: Can I pass?: using affordances to measure perceived size in virtual environments

paper_content:

Perception of an accurate sense of the scale depicted in computer graphics is important for many applications. How to best characterize the accuracy of space perception in computer graphics is a question that does not have a simple answer. This paper describes the use of perceived affordances as a way of measuring the perceptual fidelity of virtual environments with respect to how well they convey information about geometric scale. The methodology involves a verbal indication that a particular action can or cannot be performed in a viewed environment. By varying the spatial structure of the environment, these affordance judgments can be used to probe how accurately viewers are able to perceive action-relevant spatial information. The result is a measure relevant to action, less subject to bias than verbal reports of more primitive properties such as size or distance, and applicable to non-virtual-environment display systems in which the actual action cannot be performed. We demonstrate the approach in an experiment comparing one type of affordance judgment, perceived passability, with judgments of size and distance in matched real world and virtual world environments.
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paper_title: Correcting distance estimates by interacting with immersive virtual environments: Effects of task and available sensory information

paper_content:

The tendency to underestimate egocentric distances in immersive virtual environments (VEs) is not well understood. However, previous research (A. R. Richardson and D. Waller, 2007) has demonstrated that a brief period of interaction with the VE prior to making distance judgments can effectively eliminate subsequent underestimation. Here the authors examine the mechanism underlying the effect of VE interaction and the conditions that may give rise to it. In Experiment 1, after interacting with an immersive VE, participants tended to overestimate distances in the physical world, indicating that the interaction involved a recalibration of the perceptual-motor system. Experiment 2 demonstrates that visual information is not necessary (and that body-based information is necessary) during the interaction period for it to have a positive effect on subsequent distance estimation accuracy. Experiment 3 illustrates that the interaction task does not need to be goal directed in order to be effective. Language: en
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paper_title: Measurement Protocols for Medium-Field Distance Perception in Large-Screen Immersive Displays

paper_content:

How do users of virtual environments perceive virtual space? Many experiments have explored this question, but most of these have used head-mounted immersive displays. This paper reports an experiment that studied large-screen immersive displays at medium-field distances of 2 to 15 meters. The experiment measured ego-centric depth judgments in a CAVE, a tiled display wall, and a real-world outdoor field as a control condition. We carefully modeled the outdoor field to make the three environments as similar as possible. Measuring egocentric depth judgments in large-screen immersive displays requires adapting new measurement protocols; the experiment used timed imagined walking, verbal estimation, and triangulated blind walking. We found that depth judgments from timed imagined walking and verbal estimation were very similar in all three environments. However, triangulated blind walking was accurate only in the out-door field; in the large-screen immersive displays it showed under-estimation effects that were likely caused by insufficient physical space to perform the technique. These results suggest using timed imagined walking as a primary protocol for assessing depth perception in large-screen immersive displays. We also found that depth judgments in the CAVE were more accurate than in the tiled display wall, which suggests that the peripheral scenery offered by the CAVE is helpful when perceiving virtual space.
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paper_title: Revisiting the effect of quality of graphics on distance judgments in virtual environments: A comparison of verbal reports and blind walking

paper_content:

In immersive virtual environments, judgments of perceived egocentric distance are significantly underestimated, as compared with accurate performance in the real world. Two experiments assessed the influence of graphics quality on two distinct estimates of distance, a visually directed walking task and verbal reports. Experiment 1 demonstrated a similar underestimation of distances walked to previously viewed targets in both low- and high-quality virtual classrooms. In Experiment 2, participants’ verbal judgments underestimated target distances in both graphics quality environments but were more accurate in the high-quality environment, consistent with the subjective impression that high-quality environments seem larger. Contrary to previous results, we suggest that quality of graphics does influence judgments of distance, but only for verbal reports. This behavioral dissociation has implications beyond the context of virtual environments and may reflect a differential use of cues and context for verbal reports and visually directed walking.
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paper_title: Interaction with an immersive virtual environment corrects users' distance estimates.

paper_content:

OBJECTIVE ::: Two experiments examined whether prior interaction within an immersive virtual environment (VE) enabled people to improve the accuracy of their distance judgments and whether an improved ability to estimate distance generalized to other means of estimating distances. ::: ::: ::: BACKGROUND ::: Prior literature has consistently found that users of immersive VEs underestimate distances by approximately 50%. ::: ::: ::: METHOD ::: In each of the two experiments, 16 participants viewed objects in an immersive VE and estimated their distance to them by means of blindfolded walking tasks before and after interacting with the VE. ::: ::: ::: RESULTS ::: The interaction task significantly corrected users' underestimation bias to nearly veridical. Differences between pre- and post-interaction mean distance estimation accuracy were large (d = 4.63), and significant (p < .001), and they generalized across response task. ::: ::: ::: CONCLUSION ::: This finding limits the generality of the underestimation effect in VEs and suggests that distance underestimation in VEs may not be a road block to the development of VE applications. ::: ::: ::: APPLICATION ::: Potential or actual applications of this research include the improvement of VE systems requiring accurate spatial awareness.
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paper_title: Processing spatial information in the sensorimotor branch of the visual system

paper_content:

We distinguish two representations of visual space: a cognitive representation drives perception, and a sensorimotor representation controls visually guided behavior. Spatial values in the two representations are separated with the Roelofs effect: a target within an off-center frame appears biased in a location opposite the direction of the frame. The effect appears for a verbal measure (cognitive) but not for a jab at the target (sensorimotor). A 2-s response delay induces a Roelofs effect in the motor measure, showing the limit of motor memory. Motor error is not correlated with reaction time. Subjects could strike one of two identical targets, a process involving choice, without intrusion of a Roelofs effect, showing that the sensorimotor system can use its own coordinates even when a cognitive choice initiates the motor processing.
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paper_title: How does presentation method and measurement protocol affect distance estimation in real and virtual environments?

paper_content:

We conducted two experiments that compared distance perception in real and virtual environments in six visual presentation methods using either timed imagined walking or direct blindfolded walking, while controlling for several other factors that could potentially impact distance perception. Our presentation conditions included unencumbered real world, real world seen through an HMD, virtual world seen through an HMD, augmented reality seen through an HMD, virtual world seen on multiple, large immersive screens, and photo-based presentation of the real world seen on multiple, large immersive screens. We found that there was a similar degree of underestimation of distance in the HMD and large-screen presentations of virtual environments. We also found that while wearing the HMD can cause some degree of distance underestimation, this effect depends on the measurement protocol used. Finally, we found that photo-based presentation did not help to improve distance perception in a large-screen immersive display system. The discussion focuses on points of similarity and difference with previous work on distance estimation in real and virtual environments.
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paper_title: Egocentric distance perception in real and HMD-based virtual environments: the effect of limited scanning method

paper_content:

We conducted four experiments on egocentric depth perception using blind walking with a restricted scanning method in both the real and a virtual environment. Our viewing condition in all experiments was monocular. We varied the field of view (real), scan direction (real), blind walking method (real and virtual), and self-representation (virtual) over distances of 4 meters to 7 meters. The field of view varied between 21.1° and 13.6°. The scan direction varied between near-to-far scanning and far-to-near scanning. The blind walking method varied between direct blind walking and an indirect method of blind walking that matched the geometry of our laboratory. We varied self-representation between having a self-avatar (a fully tracked, animated, and first-person perspective of the user), having a static avatar (a mannequin avatar that did not move), to having no avatar (a disembodied camera view of the virtual environment). In the real environment, we find an effect of field of view; participants performed more accurately with larger field of view. In both real and virtual environments, we find an effect of blind walking method; participants performed more accurately in direct blind walking. We do not find an effect of distance underestimation in any environment, nor do we find an effect of self-representation.
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paper_title: Separate visual pathways for perception and action

paper_content:

Abstract Accumulating neuropsychological, electrophysiological and behavioural evidence suggests that the neural substrates of visual perception may be quite distinct from those underlying the visual control of actions. In other words, the set of object descriptions that permit identification and recognition may be computed independently of the set of descriptions that allow an observer to shape the hand appropriately to pick up an object. We propose that the ventral stream of projections from the striate cortex to the inferotemporal cortex plays the major role in the perceptual identification of objects, while the dorsal stream projecting from the striate cortex to the posterior parietal region mediates the required sensorimotor transformations for visually guided actions directed at such objects.
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paper_title: Throwing versus walking as indicators of distance perception in similar real and virtual environments

paper_content:

For humans to effectively interact with their environment, it is important for the visual system to determine the absolute size and distance of objects. Previous experiments performed in full-cue, real-world environments have demonstrated that blind walking to targets serves as an accurate indication of distance perception, up to about 25 m. In contrast, the same task performed in virtual environments (VEs) using head-mounted displays shows significant underestimation in walking. To date, blind walking is the only visually directed action task that has been used to evaluate distance perception in VEs beyond reaching distances. The possible influence of the response measure itself on absolute distance perception in virtual environments is currently an open question. Blind walking involves locomotion and the egocentric updating of the environment with one's own movement. We compared this measure to blind throwing, a task that involves the initiation of a movement directed by vision, but no further interaction within the environment. Both throwing and walking were compressed in the VE but accurate in the real world. We suggest that distance compression found in VEs may be a result of a general perceptual origin rather than specific to the response measure.
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paper_title: Using verbal and blind-walking distance estimates to investigate the two visual systems hypothesis

paper_content:

Verbal estimates of egocentric distance are usually too short at distances greater than several meters, yet blindfolded walking to previously viewed targets can be surprisingly accurate. We present evidence from three experiments for the existence of two visual pathways with different encodings of perceived egocentric distance. We found that (1) blind-walking estimates of egocentric distance are consistently more accurate than verbal reports; (2) an indoor versus outdoor environment selectively influences verbal reports; and (3) wearing prism lenses, which displace the visual field vertically, selectively influences the blind-walking estimates. We interpret these results in terms of the two visual systems hypothesis.
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paper_title: Distance perception in real and virtual environments

paper_content:

Two experiments were conducted to compare distance perception in real and virtual environments. In Experiment 1, adults estimated how long it would take to walk to targets in real and virtual environments by starting and stopping a stopwatch while looking at a target person standing between 20 and 120 ft away. The real environment was a large grassy lawn in front of a university building. We replicated this scene in our virtual environment using a nonstereoscopic, large screen immersive display system. We found that people underestimated time to walk in both environments for distances of 40--60 ft and beyond. However, time-to-walk estimates were virtually identical across the two environments. In Experiment 2, 10- and 12-year-old children and adults estimated time to walk in real and virtual environments both with and without vision. Adults again underestimated time to walk in both environments for distances of 60 ft and beyond. Again, their estimates were virtually identical in the real and virtual environment both with and without vision. Children's time-to-walk estimates were also very similar across the two environments under both viewing conditions. We conclude that distance perception may be better in virtual environments involving large screen immersive displays than those involving head mounted displays (HMDs).
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paper_title: Near-field distance perception in real and virtual environments using both verbal and action responses

paper_content:

Few experiments have been performed to investigate near-field egocentric distance estimation in an Immersive Virtual Environment (IVE) as compared to the Real World (RW). This article investigates near-field distance estimation in IVEs and RW conditions using physical reach and verbal report measures, by using an apparatus similar to that used by Bingham and Pagano [1998]. Analysis of our experiment shows distance compression in both the IVE and RW conditions in participants' perceptual judgments to targets. This is consistent with previous research in both action space in an IVE and reach space with Augmented Reality (AR). Analysis of verbal responses from participants revealed that participants underestimated significantly less in the virtual world as compared to the RW. We also found that verbal reports and reaches provided different results in both IVEs and RW environments.
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paper_title: Can I pass?: using affordances to measure perceived size in virtual environments

paper_content:

Perception of an accurate sense of the scale depicted in computer graphics is important for many applications. How to best characterize the accuracy of space perception in computer graphics is a question that does not have a simple answer. This paper describes the use of perceived affordances as a way of measuring the perceptual fidelity of virtual environments with respect to how well they convey information about geometric scale. The methodology involves a verbal indication that a particular action can or cannot be performed in a viewed environment. By varying the spatial structure of the environment, these affordance judgments can be used to probe how accurately viewers are able to perceive action-relevant spatial information. The result is a measure relevant to action, less subject to bias than verbal reports of more primitive properties such as size or distance, and applicable to non-virtual-environment display systems in which the actual action cannot be performed. We demonstrate the approach in an experiment comparing one type of affordance judgment, perceived passability, with judgments of size and distance in matched real world and virtual world environments.
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paper_title: Measurement Protocols for Medium-Field Distance Perception in Large-Screen Immersive Displays

paper_content:

How do users of virtual environments perceive virtual space? Many experiments have explored this question, but most of these have used head-mounted immersive displays. This paper reports an experiment that studied large-screen immersive displays at medium-field distances of 2 to 15 meters. The experiment measured ego-centric depth judgments in a CAVE, a tiled display wall, and a real-world outdoor field as a control condition. We carefully modeled the outdoor field to make the three environments as similar as possible. Measuring egocentric depth judgments in large-screen immersive displays requires adapting new measurement protocols; the experiment used timed imagined walking, verbal estimation, and triangulated blind walking. We found that depth judgments from timed imagined walking and verbal estimation were very similar in all three environments. However, triangulated blind walking was accurate only in the out-door field; in the large-screen immersive displays it showed under-estimation effects that were likely caused by insufficient physical space to perform the technique. These results suggest using timed imagined walking as a primary protocol for assessing depth perception in large-screen immersive displays. We also found that depth judgments in the CAVE were more accurate than in the tiled display wall, which suggests that the peripheral scenery offered by the CAVE is helpful when perceiving virtual space.
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paper_title: Peripheral visual information and its effect on distance judgments in virtual and augmented environments

paper_content:

A frequently observed problem in medium-field virtual environments is the underestimation of egocentric depth. This problem has been described numerous times and with widely varying degrees of severity, and although there has been considerable progress made in modifying observer behavior to compensate for these misperceptions, the question of why these errors exist is still an open issue. This paper presents the findings of a series of experiments, comprising 103 participants, that attempts to identify and quantify the source of a pattern of adaptation and improved depth judgment accuracy over time scales of less than one hour. Taken together, these experiments suggest that peripheral visual information is an important source of information for the calibration of movement within medium-field virtual environments.
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paper_title: Limited Field of View of Head-Mounted Displays Is Not the Cause of Distance Underestimation in Virtual Environments

paper_content:

Observers binocularly viewed a target placed in a large open field under two viewing conditions: unrestricted field of view and reduced field of view, as effected using a simulated head-mounted display. Observers indicated the perceived distance of the target, which ranged from 2 to 15m, using both verbal report and blind walking. For neither response was there a reliable effect of limiting the field of view on the perception of distance. This result indicates that the significant underperception of distance observed in several studies on distance perception in virtual environments is not caused by the limited field of view of the head-mounted display.
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paper_title: How does presentation method and measurement protocol affect distance estimation in real and virtual environments?

paper_content:

We conducted two experiments that compared distance perception in real and virtual environments in six visual presentation methods using either timed imagined walking or direct blindfolded walking, while controlling for several other factors that could potentially impact distance perception. Our presentation conditions included unencumbered real world, real world seen through an HMD, virtual world seen through an HMD, augmented reality seen through an HMD, virtual world seen on multiple, large immersive screens, and photo-based presentation of the real world seen on multiple, large immersive screens. We found that there was a similar degree of underestimation of distance in the HMD and large-screen presentations of virtual environments. We also found that while wearing the HMD can cause some degree of distance underestimation, this effect depends on the measurement protocol used. Finally, we found that photo-based presentation did not help to improve distance perception in a large-screen immersive display system. The discussion focuses on points of similarity and difference with previous work on distance estimation in real and virtual environments.
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paper_title: DISTANCE ESTIMATION IN A 3-D IMAGING DISPLAY

paper_content:

Visual information imaging systems are a central feature in the latest generation of aircraft. However, no imaging displays are yet able to provide an exact simulation of the real world viewed directly and this may account for some loss in visual performance when compared to direct vision. One such decrement in performance is in judgment of distance. This article reports on an experiment in which judgments of distance of targets were obtained from videotaped images of targets in a natural outdoor scene. Presentations were made under three conditions: (1) stereo with near zero disparities; (2) stereo with far zero disparities; and (3) binocular nonstereo (biocular) viewing. Results revealed that the most accurate distance estimations were in the stereo-near condition. In this condition, the optical axes of the sensors converged at the plane of presentation. These findings have implications for the design of cockpit imaging displays and flight simulators.
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paper_title: Estimation of distances in virtual environments using size constancy

paper_content:

It is reported in the literature that distances from ::: the observer are underestimated more in virtual environments ::: (VEs) than in physical world conditions. On the other hand ::: estimation of size in VEs is quite accurate and follows a ::: size-constancy law when rich cues are present. This study ::: investigates how estimation of distance in a CAVETM ::: environment is affected by poor and rich cue conditions, subject ::: experience, and environmental learning when the position of the ::: objects is estimated using an experimental paradigm that ::: exploits size constancy. ::: A group of 18 healthy participants was asked to move a ::: virtual sphere controlled using the wand joystick to the position ::: where they thought a previously-displayed virtual cube ::: (stimulus) had appeared. Real-size physical models of the virtual ::: objects were also presented to the participants as a reference of ::: real physical distance during the trials. An accurate estimation ::: of distance implied that the participants assessed the relative size ::: of sphere and cube correctly. The cube appeared at depths ::: between 0.6 m and 3 m, measured along the depth direction of ::: the CAVE. The task was carried out in two environments: a ::: poor cue one with limited background cues, and a rich cue one ::: with textured background surfaces. ::: It was found that distances were underestimated in both poor ::: and rich cue conditions, with greater underestimation in the ::: poor cue environment. The analysis also indicated that factors ::: such as subject experience and environmental learning were not ::: influential. However, least square fitting of Stevens’ power law ::: indicated a high degree of accuracy during the estimation of ::: object locations. This accuracy was higher than in other studies ::: which were not based on a size-estimation paradigm. Thus as ::: indirect result, this study appears to show that accuracy when ::: estimating egocentric distances may be increased using an ::: experimental method that provides information on the relative ::: size of the objects used.
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paper_title: The effects of head-mounted display mechanical properties and field of view on distance judgments in virtual environments

paper_content:

Research has shown that people are able to judge distances accurately in full-cue, real-world environments using visually directed actions. However, in virtual environments viewed with head-mounted display (HMD) systems, there is evidence that people act as though the virtual space is smaller than intended. This is a surprising result given how well people act in real environments. The behavior in the virtual setting may be linked to distortions in the available visual cues or to a person's ability to locomote without vision. Either could result from issues related to added mass, moments of inertia, and restricted field of view in HMDs. This article describes an experiment in which distance judgments based on normal real-world and HMD viewing are compared with judgments based on real-world viewing while wearing two specialized devices. One is a mock HMD, which replicated the mass, moments of inertia, and field of view of the HMD and the other an inertial headband designed to replicate the mass and moments of inertia of the HMD, but constructed to not restrict the field of view of the observer or otherwise feel like wearing a helmet. Distance judgments using the mock HMD showed a statistically significant underestimation relative to the no restriction condition but not of a magnitude sufficient to account for all the distance compression seen in the HMD. Indicated distances with the inertial headband were not significantly smaller than those made with no restrictions.
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paper_title: Estimating Distance in Real and Virtual Environments: Does Order Make a Difference?

paper_content:

In this investigation, we examined how the order in which people experience real and virtual environments influences their distance estimates. Participants made two sets of distance estimates in one of the following conditions: (1) real environment first, virtual environment second; (2) virtual environment first, real environment second; (3) real environment first, real environment second; or (4) virtual environment first, virtual environment second. In Experiment 1, the participants imagined how long it would take to walk to targets in real and virtual environments. The participants’ first estimates were significantly more accurate in the real than in the virtual environment. When the second environment was the same as the first environment (real-real and virtual-virtual), the participants’ second estimates were also more accurate in the real than in the virtual environment. When the second environment differed from the first environment (real-virtual and virtual-real), however, the participants’ second estimates did not differ significantly across the two environments. A second experiment, in which the participants walked blindfolded to targets in the real environment and imagined how long it would take to walk to targets in the virtual environment, replicated these results. These subtle yet persistent order effects suggest that memory can play an important role in distance perception.
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paper_title: Display size does not affect egocentric distance perception of naturalistic stimuli

paper_content:

Although people are quite accurate in visually perceiving absolute egocentric distances in real environments up to 20m, they usually underestimate distances in virtual environments presented through head-mounted displays (HMDs). Several previous studies examined different potential factors, but none of these factors could convincingly explain the observed distance compressionin HMDs. In this study, we investigated the potential influence of naturalistic stimulus presentation and display size -- a factor largely overlooked in previous studies. To this end, we used an indirect blindfolded walking task to previously-seen targets. Participants viewed photos of targets located at various distances on the ground through different-sized displays (HMD, 24" monitor, and 50" screen) and walked without vision to where they thought the location of the target was. Real-world photographs were used to avoid potential artifacts of computer-graphics stimuli. Displays were positioned to provide identical fields of view (32° x 24°). Distance judgments were unexpectedly highly accurate and showed no signs of distance compression for any of the displays. Moreover, display size did not affect distance perception, and performance was virtually identical to a real world baseline, where real-world targets were viewed through 32° x 24° field of view restrictors. A careful analysis of potential underlying factors suggests that the typically-observed distance compression for HMDs might be overcome by using naturalistic real-world stimuli. This might also explain why display size did not affect distance judgments.
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paper_title: Depth Perception in Virtual Reality: Distance Estimations in Peri- and Extrapersonal Space

paper_content:

ABSTRACT The present study investigated depth perception in virtual environments. Twenty-three participants verbally estimated ten distances between 40 cm and 500 cm in three different virtual environments in two conditions: (1) only one target was presented or (2) ten targets were presented at the same time. Additionally, the presence of a metric aid was varied. A questionnaire assessed subjective ratings about physical complaints (e.g., headache), the experience in the virtual world (e.g., presence), and the experiment itself (self-evaluation of the estimations). Results show that participants underestimate the virtual distances but are able to perceive the distances in the right metric order even when only very simple virtual environments are presented. Furthermore, interindividual differences and intraindividual stabilities can be found among participants, and neither the three different virtual environments nor the metric aid improved depth estimations. Estimation performance is better in peripersona...
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paper_title: The Right View from the Wrong Location: Depth Perception in Stereoscopic Multi-User Virtual Environments

paper_content:

Stereoscopic depth cues improve depth perception and increase immersion within virtual environments (VEs). However, improper display of these cues can distort perceived distances and directions. Consider a multi-user VE, where all users view identical stereoscopic images regardless of physical location. In this scenario, cues are typically customized for one "leader" equipped with a head-tracking device. This user stands at the center of projection (CoP) and all other users ("followers") view the scene from other locations and receive improper depth cues. This paper examines perceived depth distortion when viewing stereoscopic VEs from follower perspectives and the impact of these distortions on collaborative spatial judgments. Pairs of participants made collaborative depth judgments of virtual shapes viewed from the CoP or after displacement forward or backward. Forward and backward displacement caused perceived depth compression and expansion, respectively, with greater compression than expansion. Furthermore, distortion was less than predicted by a ray-intersection model of stereo geometry. Collaboration times were significantly longer when participants stood at different locations compared to the same location, and increased with greater perceived depth discrepancy between the two viewing locations. These findings advance our understanding of spatial distortions in multi-user VEs, and suggest a strategy for reducing distortion.
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paper_title: Accommodation and Size-Constancy of Virtual Objects

paper_content:

Accommodation has been suspected as a contributor to size illusions in virtual environments (VE) due to the lack of appropriate accommodative stimuli in a VE for the objects displayed. Previous experiments examining size-constancy in VE have shown that monocular cues to depth that accompany the object are a major contributor to correct size perception. When these accompanying cues are removed perceived size varied with the object's distance from the subject, i.e., visual angle. If accommodation were the dominant mechanism contributing to a visual angle response [due to its action to keep physical objects clear] in this condition, an open-loop accommodation viewing condition might restore size-constancy to this condition. Pinhole apertures were used to open-loop accommodation and examine if size-constancy might be restored when few accompanying monocular cues to depth were present. Visual angle performance when viewing a low cue environment was found with and without the use of the pinhole apertures. Thus, these results signify that accommodation does not play a dominate role in the loss of size-constancy in sparse visual environments often used in VE. These results suggest that size-constancy is driven by the inclusion of the remaining monocular cues to depth in VE as it is in the physical world.
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paper_title: On the Determinants of Size-Constancy in a Virtual Environment

paper_content:

—An important aspect of a subject’s perception of ::: virtual objects in a virtual environment is whether the size of the ::: object is perceived as it would be in the physical world, which is ::: named size-constancy. The ability of subjects to appreciate ::: size-constancy in an immersive virtual environment was studied ::: while scene complexity, stereovision and motion parallax visual ::: factors were manipulated resulting in twelve different viewing ::: conditions. Under each visual condition, 18 subjects made size ::: judgments of a virtual object displayed at five different distances ::: from them. Responses from the majority of our population ::: demonstrated that scene complexity and stereovision have a ::: significant impact on subjects’ ability to appreciate size-constancy. ::: In contrast, motion parallax produced by moving the virtual ::: environment or by the movements of the observer alone proved ::: not to be a significant factor in determining size-constancy ::: performance. Consequently, size-constancy is best obtained when ::: scene complexity and stereovision are components of the viewing ::: conditions.
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paper_title: Judging Perceived and Traversed Distance in Virtual Environments

paper_content:

The ability to accurately estimate distance is an essential component of navigating large-scale spaces. Although the factors that influence distance estimation have been a topic of research in real-world environments for decades and are well known, research on distance estimation in virtual environments (VEs) has only just begun. Initial investigations of distance estimation in VEs suggest that observers are less accurate in estimating distance in VEs than in the real world (Lampton et al., 1995). Factors influencing distance estimates may be divided into those affecting perceived distance (visual cues only) and those affecting traversed distance to include visual, cognitive, and proprioceptive cues. To assess the contribution of the various distance cues in VEs, two experiments were conducted. The first required a static observer to estimate the distance to a cylinder placed at various points along a 130-foot hallway. This experiment examined the effects of floor texture, floor pattern, and object size on distance estimates in a VE. The second experiment required a moving observer to estimate route segment distances and total route distances along four routes, each totaling 1210 feet. This experiment assessed the effects of movement method, movement speed, compensatory cues, and wall texture density. Results indicate that observers underestimate distances both in VEs and in the real world, but the underestimates are more extreme in VEs. Texture did not reliably affect the distance estimates, providing no compensation for the gross underestimates of distance in VE. Traversing a distance improves the ability to estimate that distance, but more natural means of moving via a treadmill do not necessarily improve distance estimates over traditional methods of moving in VE (e.g., using a joystick). The addition of compensatory cues (tone every 10 feet traversed on alternate route segments) improves VE distance estimation to almost perfect performance.
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paper_title: Virtual prototype visualization: a size perception study

paper_content:

In this experiment, carried out at Renault, we studied size perception in virtual environments. We compared 1:1 scale perception of a cockpit through two different virtual reality systems: a Head Mounted Display (HMD), which can be used as virtual or augmented reality system, and a cylindrical screen vs. the physical 1:1 scale. We show that differences exist between size perception using the HMD, and using the cylindrical screen.
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paper_title: Depth Perception Within Virtual Environments: Comparison Between two Display Technologies

paper_content:

Depth perception is one of the key issues in virtual reality. Many questions within this area are still under investigation including the egocentric distance misestimation. In this paper we describe an experiment confirming distance underestimation from another point of view. The approach we developed is based on a very simple task: subjects had to compare relative depths of two virtual objects. The experiment compared performance using head mounted display and stereo- scopic widescreen display to evaluate which visual cues subjects use to estimate depth of virtual objects. To minimize motoric effects, subjects were seated and their estimations were only verbal. Likewise, to avoid the well known effects of apparent size, namely the size-distance invariance, the experiment was also performed with conflict sequences: the presented objects had the same apparent sizes with different depths or the same depth but different physical sizes. The obtained results show significant differences between the two devices and confirm the distance misestimation phenomenon for head mounted display. Moreover, changing the background color or the shape of the presented objects also had an influence on subjects' performance.
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paper_title: Distance perception in real and virtual environments

paper_content:

Two experiments were conducted to compare distance perception in real and virtual environments. In Experiment 1, adults estimated how long it would take to walk to targets in real and virtual environments by starting and stopping a stopwatch while looking at a target person standing between 20 and 120 ft away. The real environment was a large grassy lawn in front of a university building. We replicated this scene in our virtual environment using a nonstereoscopic, large screen immersive display system. We found that people underestimated time to walk in both environments for distances of 40--60 ft and beyond. However, time-to-walk estimates were virtually identical across the two environments. In Experiment 2, 10- and 12-year-old children and adults estimated time to walk in real and virtual environments both with and without vision. Adults again underestimated time to walk in both environments for distances of 60 ft and beyond. Again, their estimates were virtually identical in the real and virtual environment both with and without vision. Children's time-to-walk estimates were also very similar across the two environments under both viewing conditions. We conclude that distance perception may be better in virtual environments involving large screen immersive displays than those involving head mounted displays (HMDs).
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paper_title: Egocentric distance judgments in a large screen display immersive virtual environment

paper_content:

People underestimate egocentric distances in head-mounted display virtual environments, as compared to estimates done in the real world. Our work investigates whether distances are still compressed in a large screen display immersive virtual environment, where participants are able to see their own body surrounded by the virtual environment. We conducted our experiment in both the real world using a real room and the large screen display immersive virtual environment using a 3D model of the real room. Our results showed a significant underestimation of verbal reports of egocentric distances in the large screen display immersive virtual environment, while the distance judgments of the real world were closer to veridical. Moreover, we observed a significant effect of distances in both environments. In the real world closer distances were slightly underestimated, while further distances were slightly overestimated. In contrast to the real world in the virtual environment participants overestimated closer distances (up to 2.5m) and underestimated distances that were further than 3m. A possible reason for this effect of distances in the virtual environment may be that participants perceived stereo cues differently when the target was projected on the floor versus on the front of the large screen.
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paper_title: Stereoscopic stimuli are not used in absolute distance evaluation to proximal objects in multicue virtual environment

paper_content:

Many authors report that binocular vision plays an important role in the evaluation of the distance to scenery objects. Furthermore, it was observed that narrow (<20°) angular visual observation field, called field of view, causes underestimation of distances to objects in natural scenes. In a series of experiments we studied if distances were underestimated for larger fields of views (60°, 90° and 120°) and if binocular vision could correct distance estimation. We have also studied distance estimation in virtual environments in the same observation conditions as it is known that it may be poorer because of the lack or bias of visual stimuli. Observers had to estimate proximal distances in real and virtual (large fields of view head mounted display and power wall) scenes of a car interior. We have found that there is a strong underestimation of distances in observing proximal objects (≤50cm) in a reduced field of view for both real and virtual scenes and more the field of view is reduced, more observers underestimate distances. Furthermore underestimation is stronger in virtual environments for the same objects than in real ones. We have also compared distance estimations between monocular and binocular observation conditions and found no significant differences for all fields of view. Our results show that binocular vision is not allowing better distance estimation than monocular vision. These results suggest an unexpectedly weak effect of binocular vision on the observation of distances of proximal objects in multi-cue environments.
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paper_title: Nonvisually Guided Locomotion to a Previously Viewed Target in Real and Virtual Environments

paper_content:

Comparing human performance in a virtual environment (VE) with performance in the real world can provide clues about which aspects of VE technology require improvement. Using a technique previously shown to measure real-world distance judgments accurately, we compared performance in a real-world environment with performance in a virtual model of that environment. The technique required participants to walk without vision to a target after viewing it for 10 s. VE distance judgments averaged 85% of the target distance, whereas real-world judgments averaged 92%. The magnitude of the relative errors in the VE was twice that in the real world, indicating that the VE degraded distance judgments. Our analysis suggests that VE performance deficits result either from poor binocular disparity cues or from distortion of pictorial depth cues. Actual or potential applications of this research include the development of virtual environments for training and the design of visual displays for virtual simulations.
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paper_title: Measurement Protocols for Medium-Field Distance Perception in Large-Screen Immersive Displays

paper_content:

How do users of virtual environments perceive virtual space? Many experiments have explored this question, but most of these have used head-mounted immersive displays. This paper reports an experiment that studied large-screen immersive displays at medium-field distances of 2 to 15 meters. The experiment measured ego-centric depth judgments in a CAVE, a tiled display wall, and a real-world outdoor field as a control condition. We carefully modeled the outdoor field to make the three environments as similar as possible. Measuring egocentric depth judgments in large-screen immersive displays requires adapting new measurement protocols; the experiment used timed imagined walking, verbal estimation, and triangulated blind walking. We found that depth judgments from timed imagined walking and verbal estimation were very similar in all three environments. However, triangulated blind walking was accurate only in the out-door field; in the large-screen immersive displays it showed under-estimation effects that were likely caused by insufficient physical space to perform the technique. These results suggest using timed imagined walking as a primary protocol for assessing depth perception in large-screen immersive displays. We also found that depth judgments in the CAVE were more accurate than in the tiled display wall, which suggests that the peripheral scenery offered by the CAVE is helpful when perceiving virtual space.
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paper_title: An application driven comparison of depth perception on desktop 3D displays

paper_content:

Desktop 3D displays vary in their optical design and this results in a significant variation in the way in which stereo images are physically displayed on different 3D displays. When precise depth judgements need to be made these differences may become critical to task performance. Applications where this is a particular issue include medical imaging, geoscience and scientific visualization. We investigate perceived depth thresholds for four classes of desktop 3D display; full resolution, row interleaved, column interleaved and colour-column interleaved. Given the same input image resolution we calculate the physical view resolution for each class of display to geometrically predict its minimum perceived depth threshold. To verify our geometric predictions we present the design of a task where viewers are required to judge which of two neighboring squares lies in front of the other. We report results from a trial using this task where participants are randomly asked to judge whether they can perceive one of four levels of image disparity (0,2,4 and 6 pixels) on seven different desktop 3D displays. The results show a strong effect and the task produces reliable results that are sensitive to display differences. However, we conclude that depth judgement performance cannot always be predicted from display geometry alone. Other system factors, including software drivers, electronic interfaces, and individual participant differences must also be considered when choosing a 3D display to make critical depth judgements.
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paper_title: Peripheral visual information and its effect on distance judgments in virtual and augmented environments

paper_content:

A frequently observed problem in medium-field virtual environments is the underestimation of egocentric depth. This problem has been described numerous times and with widely varying degrees of severity, and although there has been considerable progress made in modifying observer behavior to compensate for these misperceptions, the question of why these errors exist is still an open issue. This paper presents the findings of a series of experiments, comprising 103 participants, that attempts to identify and quantify the source of a pattern of adaptation and improved depth judgment accuracy over time scales of less than one hour. Taken together, these experiments suggest that peripheral visual information is an important source of information for the calibration of movement within medium-field virtual environments.
---
paper_title: Accommodation, occlusion, and disparity matching are used to guide reaching: a comparison of actual versus virtual environments.

paper_content:

The authors used a virtual environment to investigate visual control of reaching and monocular and binocular perception of egocentric distance, size, and shape. With binocular vision, the results suggested use of disparity matching. This was tested and confirmed in the virtual environment by eliminating other information about contact of hand and target. Elimination of occlusion of hand by target destabilized monocular but not binocular performance. Because the virtual environment entails accommodation of an image beyond reach, the authors predicted overestimation of egocentric distances in the virtual relative to actual environment. This was confirmed. The authors used -2 diopter glasses to reduce the focal distance in the virtual environment. Overestimates were reduced by half. The authors conclude that calibration of perception is required for accurate feedforward reaching and that disparity matching is optimal visual information for calibration.
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paper_title: Visual fatigue caused by viewing stereoscopic motion images: Background, theories, and observations

paper_content:

The background, theories, and observations on visual stress possibly caused by viewing stereoscopic motion images are reviewed. Visual fatigue caused by stereoscopic images is a safety issue. Fatigue is possible caused by the discrepancy between accommodative and convergence stimuli that are included in the image. Studies on accommodation and convergence are surveyed and an explanation regarding the characteristics of these functions is offered. Studies in the literature on changes in oculomotor function after viewing stereoscopic images, including changes in pupillary responses, are discussed. Evaluation of visual fatigue, particularly in relation to different methods of viewing stereoscopic displays is described.
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paper_title: The task-dependent use of binocular disparity and motion parallax information

paper_content:

Abstract Binocular disparity and motion parallax are powerful cues to the relative depth between objects. However to recover absolute depth, either additional scaling parameters are required to calibrate the information provided by each cue, or it can be recovered through the combination of information from both cues (Richards, W. (1985). Structure from stereo and motion. Journal of the Optical Society of America , 2 , 343–349). However, not all tasks necessarily require a full specification of the absolute depth structure of a scene and so psychophysical performance may vary depending on the amount of information available, and the degree to which absolute depth structure is required. The experiments reported here used three different tasks that varied in the type of geometric information required in order for them to be completed successfully. These included a depth nulling task, a depth-matching task, and an absolute depth judgement (shape) task. Real world stimuli were viewed (i) monocularly with head movements, (ii) binocularly and static, or (iii) binocularly with head movements. No effect of viewing condition was found whereas there was a large effect of task. Performance was accurate on the matching and nulling tasks and much less accurate on the shape task. The fact that the same perceptual distortions were not evident in all tasks suggests that the visual system can switch strategy according to the demands of the particular task. No evidence was found to suggest that the visual system could exploit the simultaneous presence of disparity and motion parallax.
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paper_title: Perceiving layout and knowing distances: The integration, relative potency, and contextual use of different information about depth

paper_content:

Publisher Summary ::: This chapter discusses three questions: Why are there so many sources of information about layout? How is it that one perceives layout with near-metric accuracy when none of these sources yields metric information about it? Can one not do better, theoretically, in understanding the perception of layout than simply make a list? The answer to the first question begins with Todd's answer. Perceiving layout is extremely important to human beings, so important that it must be redundantly specified so that the redundancy can guard against the failure of any given source or the failure of any of the assumptions on which a given source is based. However, information redundancy is only part of the answer. Different sources of information about layout metrically reinforce and contrast with each other, providing a powerful network of constraints. The answer to the second proceeds from this idea. Through the analysis of depth-threshold functions for nine different sources of information about layout, one can begin to understand how those sources of information sharing the same-shaped functions across distances can help ramify judgments of layout by serving to correct measurement errors in each. Third, on the basis of the analyses and the pattern of functions, it suggests that list making has misled about space and layout. Psychologists and other vision scientists have generally considered layout, space, and distance as a uniform commodity in which observers carry out their day-to-day activities.
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paper_title: Absolute motion parallax weakly determines visual scale in real and virtual environments

paper_content:

The determinants of visual scale (size and distance) under monocular viewing are still largely unknown. The problem of visual scale under monocular viewing becomes readily apparent when one moves about within a virtual environment. It might be thought that the absolute motion parallax of stationary objects (both in real and virtual environments), under the assumption of the stationarity, would immediately determine their apparent size and distance for an observer who is walking about. We sought to assess the effectiveness of observer- produced motion parallax in scaling apparent size and distance within near space. We had subjects judge the apparent size and distance of real and virtual objects under closely matched conditions Real and virtual targets were 4 spheres seen in darkness at eye level. the targets ranges in diameter from 3.7 cm to 14.8 cm and were viewed monocularly from difference distances, with a subset of the size/distance combinations resulting in projectively equivalent stimuli at the viewing origin. subjects moved laterally plus and minus 1 m to produce large amounts of motion parallax. when angular size was held constant and motion parallax acted as a differential cue to target size and distance, judged size varied by a facto or 1.67 and 1.18 for the real and virtual environments, respectively, well short of the fourfold change in distal size. Similarly, distance judgments varied by factors of only 1.74 and 1.07 respectively. We conclude that absolute motion parallax only weakly determines the visual scale of nearby objects varying over a fourfold range in size.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
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paper_title: DISTANCE ESTIMATION IN A 3-D IMAGING DISPLAY

paper_content:

Visual information imaging systems are a central feature in the latest generation of aircraft. However, no imaging displays are yet able to provide an exact simulation of the real world viewed directly and this may account for some loss in visual performance when compared to direct vision. One such decrement in performance is in judgment of distance. This article reports on an experiment in which judgments of distance of targets were obtained from videotaped images of targets in a natural outdoor scene. Presentations were made under three conditions: (1) stereo with near zero disparities; (2) stereo with far zero disparities; and (3) binocular nonstereo (biocular) viewing. Results revealed that the most accurate distance estimations were in the stereo-near condition. In this condition, the optical axes of the sensors converged at the plane of presentation. These findings have implications for the design of cockpit imaging displays and flight simulators.
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paper_title: Technical Section: A review of virtual environments for training in ball sports

paper_content:

There is growing interest in utilising virtual environments (VEs) in the context of sports. In particular there is a desire to be able to improve sensorimotor skills rather than just using a VE as a tool for strategy analysis, or entertainment. The range of skills required across all different sports is very large and varied. This review of the state-of-the-art, therefore focuses on just ball sports, and was carried out as part of a current project developing training tools for rugby. A VE needs to provide realistic rendering of the sports scene to achieve good perceptual fidelity. More important for a sport-themed VE is high functional fidelity, which requires an accurate physics model of a complex environment, real time response, and a natural user interface. The goal is to provide multiple scenarios to players at different levels of difficulty, providing them with improved skills that can be applied directly to the real sports arena. The typical hardware and software components needed are identified in the paper, and important psychological factors that should be considered are discussed. The challenges that need to be overcome are identified and illustrated with examples from recent projects in this area.
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paper_title: The visual control of reaching and grasping: Binocular disparity and motion parallax.

paper_content:

The primary visual sources of depth and size information are binocular cues and motion parallax. Here, the authors determine the efficacy of these cues to control prehension by presenting them in isolation from other visual cues. When only binocular cues were available, reaches showed normal scaling of the transport and grasp components with object distance and size. However, when only motion parallax was available, only the transport component scaled reliably. No additional increase in scaling was found when both cues were available simultaneously. Therefore, although equivalent information is available from binocular and motion parallax information, the latter may be of relatively limited use for the control of the grasp. Binocular disparity appears selectively important for the control of the grasp.
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paper_title: Perceptual issues in augmented reality

paper_content:

Between the extremes of real life and Virtual Reality lies the spectrum of Mixed Reality, in which views of the real world are combined in some proportion with views of a virtual environment. Combining direct view, stereoscopic video, and stereoscopic graphics, Augmented Reality describes that class of displays that consists primarily of a real environment, with graphic enhancements or augmentations. Augmented Virtuality describes that class of displays that enhance the virtual experience by adding elements of the real environment. All Mixed Reality systems are limited in their capability of accurately displaying and controlled all relevant depth cues, and as a result, perceptual biases can interfere with task performance. In this paper we identify and discuss eighteen issues that pertain to Mixed Reality in general, and Augmented Reality in particular.
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paper_title: Virtual Reality: How Much Immersion Is Enough?

paper_content:

Solid evidence of virtual reality's benefits has graduated from impressive visual demonstrations to producing results in practical applications. Further, a realistic experience is no longer immersion's sole asset. Empirical studies show that various components of immersion provide other benefits - full immersion is not always necessary. The goal of immersive virtual environments (VEs) was to let the user experience a computer-generated world as if it were real - producing a sense of presence, or "being there," in the user's mind.
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paper_title: Depth Perception and the Perception of Events

paper_content:

Three fundamental questions are addressed: (1) What are the effective sources of optical information for perceiving spatial relationships and events? Complex natural environments provide a plethora of information potentially related to spatial layout. Psychophysical research investigates the efficacy and perceptual processing of these potential cues to depth and events. (2) How is this information combined by the perceptual system? Viewed in isolation, individual cues typically do not fully specify the environmental properties to which they relate. In general, the rules for projecting three-dimensional layout onto the retina are unambiguously defined, whereas the inverse operation—from the image to the three-dimensional projected scene—is not. (3) Do people perceive space and events accurately? Certainly, people act in the environment as if they represent its spatial relationships accurately; however, effective action can often be achieved without geometrically correct representations. From a pragmatic perspective, perceptual representations are accurate to the degree that they provide effective guidance for behavior. This issue is developed and discussed throughout the chapter. ::: ::: ::: Keywords: ::: ::: binocular disparity; ::: depth cues; ::: ocular-motor depth cues; ::: optical flow; ::: perceptual organization; ::: perspective; ::: spatial layout
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paper_title: Accommodation and Size-Constancy of Virtual Objects

paper_content:

Accommodation has been suspected as a contributor to size illusions in virtual environments (VE) due to the lack of appropriate accommodative stimuli in a VE for the objects displayed. Previous experiments examining size-constancy in VE have shown that monocular cues to depth that accompany the object are a major contributor to correct size perception. When these accompanying cues are removed perceived size varied with the object's distance from the subject, i.e., visual angle. If accommodation were the dominant mechanism contributing to a visual angle response [due to its action to keep physical objects clear] in this condition, an open-loop accommodation viewing condition might restore size-constancy to this condition. Pinhole apertures were used to open-loop accommodation and examine if size-constancy might be restored when few accompanying monocular cues to depth were present. Visual angle performance when viewing a low cue environment was found with and without the use of the pinhole apertures. Thus, these results signify that accommodation does not play a dominate role in the loss of size-constancy in sparse visual environments often used in VE. These results suggest that size-constancy is driven by the inclusion of the remaining monocular cues to depth in VE as it is in the physical world.
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paper_title: Quantifying the benefits of immersion for collaboration in virtual environments

paper_content:

Collaborative Virtual Environments allow multiple users to interact collaboratively while taking advantage of the perceptual richness that Virtual Environments (VEs) provide. In this paper, we demonstrate empirically that increasing the level of immersion in a VE can have a beneficial effect on the usability of that environment in a collaborative context. We present the results of a study in which we varied two immersive factors, stereo and head tracking, within the context of a two person collaborative task. Our results indicate that stereo can have a positive effect on task performance; that different levels of immersion have effects that vary with gender; and that varying the level of immersion has a pronounced effect on communication between users. These results show that the level of immersion can play an important role in determining user performance on some collaborative tasks.
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paper_title: On the Determinants of Size-Constancy in a Virtual Environment

paper_content:

—An important aspect of a subject’s perception of ::: virtual objects in a virtual environment is whether the size of the ::: object is perceived as it would be in the physical world, which is ::: named size-constancy. The ability of subjects to appreciate ::: size-constancy in an immersive virtual environment was studied ::: while scene complexity, stereovision and motion parallax visual ::: factors were manipulated resulting in twelve different viewing ::: conditions. Under each visual condition, 18 subjects made size ::: judgments of a virtual object displayed at five different distances ::: from them. Responses from the majority of our population ::: demonstrated that scene complexity and stereovision have a ::: significant impact on subjects’ ability to appreciate size-constancy. ::: In contrast, motion parallax produced by moving the virtual ::: environment or by the movements of the observer alone proved ::: not to be a significant factor in determining size-constancy ::: performance. Consequently, size-constancy is best obtained when ::: scene complexity and stereovision are components of the viewing ::: conditions.
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paper_title: Presence in virtual environments as a function of visual and auditory cues

paper_content:

The paper reports the results of two experiments each investigating the sense of presence within visual and auditory virtual environments. The variables for the studies included the presence or absence of head tracking, the presence or absence of stereoscopic cues, the geometric field of view (GFOV) used to design the visual display, the presence or absence of spatialized sound and the addition of spatialized versus non-spatialized sound to a stereoscopic display. In both studies, subjects were required to navigate a virtual environment and to complete a questionnaire designed to ascertain the level of presence experienced by the participant within the virtual world. The results indicated that the reported level of presence was significantly higher when head tracking and stereoscopic cues were provided, with more presence associated with a 50 and 90 degree GFOV when compared to a narrower 10 degree GFOV. Further, the addition of spatialized sound did significantly increase ones sense of presence in the virtual environment, on the other hand, the addition of spatialized sound did not increase the apparent realism of that environment.
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paper_title: Focus cues affect perceived depth

paper_content:

Depth information from focus cuesVaccommodation and the gradient of retinal blurVis typically incorrect in threedimensional (3-D) displays because the light comes from a planar display surface. If the visual system incorporates information from focus cues into its calculation of 3-D scene parameters, this could cause distortions in perceived depth even when the 2-D retinal images are geometrically correct. In Experiment 1 we measured the direct contribution of focus cues to perceived slant by varying independently the physical slant of the display surface and the slant of a simulated surface specified by binocular disparity (binocular viewing) or perspective/texture (monocular viewing). In the binocular condition, slant estimates were unaffected by display slant. In the monocular condition, display slant had a systematic effect on slant estimates. Estimates were consistent with a weighted average of slant from focus cues and slant from disparity/texture, where the cue weights are determined by the reliability of each cue. In Experiment 2, we examined whether focus cues also have an indirect effect on perceived slant via the distance estimate used in disparity scaling. We varied independently the simulated distance and the focal distance to a disparity-defined 3-D stimulus. Perceived slant was systematically affected by changes in focal distance. Accordingly, depth constancy (with respect to simulated distance) was significantly reduced when focal distance was held constant compared to when it varied appropriately with the simulated distance to the stimulus. The results of both experiments show that focus cues can contribute to estimates of 3-D scene parameters. Inappropriate focus cues in typical 3-D displays may therefore contribute to distortions in perceived space.
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paper_title: Virtual reality system effects on size-distance judgements in a virtual environment

paper_content:

The paper provides an assessment of how selected properties of a virtual reality system impact size-distance judgments in a virtual environment. Manipulations are made in viewing conditions (biocular vs. stereoscopic), image resolution, field of view, scene contrast and target distance, while subjects attempt to match the attributes of a comparison object with a standard object. General findings suggest that under more natural viewing conditions, size-distance judgements in virtual environments differ from those found previously in physical environments whereas, under impoverished conditions, performance differences between the two environments are similar.
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paper_title: Visual Discomfort and Visual Fatigue of Stereoscopic Displays: A Review

paper_content:

Visual discomfort has been the subject of considerable research in relation to stereoscopic and autostereoscopic displays. In this paper, the importance of various causes and aspects of visual discomfort is clarified. When disparity values do not surpass a limit of 1°, which still provides sufficient range to allow satisfactory depth perception in stereoscopic television, classical determinants such as excessive binocular parallax and accommodation-vergence conflict appear to be of minor importance. Visual discomfort, however, may still occur within this limit and we believe the following factors to be the most pertinent in contributing to this: (1) temporally changing demand of accommodation-vergence linkage, e.g., by fast motion in depth; (2) three-dimensional artifacts resulting from insufficient depth information in the incoming data signal yielding spatial and temporal inconsistencies; and (3) unnatural blur. In order to adequately characterize and understand visual discomfort, multiple types of measurements, both objective and subjective, are required.
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paper_title: Virtual prototype visualization: a size perception study

paper_content:

In this experiment, carried out at Renault, we studied size perception in virtual environments. We compared 1:1 scale perception of a cockpit through two different virtual reality systems: a Head Mounted Display (HMD), which can be used as virtual or augmented reality system, and a cylindrical screen vs. the physical 1:1 scale. We show that differences exist between size perception using the HMD, and using the cylindrical screen.
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paper_title: Comparison of Two Indicators of Perceived Egocentric Distance Under Full-Cue and Reduced-Cue Conditions

paper_content:

It has not been established that walking without vision to previewed targets is indeed controlled by perceived distance. To this end, we compared walking and verbal report as distance indicators, looking for a tight covariation in responses that would indicate control by a common variable. Targets from 79-500 cm away were presented under dark and well-lit conditions. Both verbal reports and walking indicated overestimation of near targets and underestimation of far targets under dark viewing conditions. Moreover, the finding that verbally reported distance plotted essentially as a single-valued function of walked distance and vice versa is evidence that both indicators were responding to the same internal variable, ostensibly perceived distance. In addition, binocular parallax, absolute motion parallax, and angular elevation were evaluated as distance cues, and only angular elevation exerted a large influence on perceived distance. When people are asked to view an object in a well-lit environment and then attempt to walk over to it with eyes closed, they do so, on average, without large systematic error. This finding has been documented by several researchers (Corlett, Patla, & Williams, 1985; Elliott, 1986,
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paper_title: Motion parallax and absolute distance.

paper_content:

Abstract : The accuracy of absolute distance estimation based on monocular motion parallax was determined both before and after specific training. With the usual distance information eliminated, subjects either held their heads stationary or rhythmically rotated their heads from side to side while judging the distance of stimuli placed 4-15 ft. away. Before training, head movement produced more accurate judgments than head fixed. After only 10 training trials, accurate judgments based on motion parallax were obtained. Results with a textured background were better than results with a white background only when the subjects were not given any direct information about motion parallax. Good results were also obtained for motion parallax relative to a near reference object (2.5 ft. away). The results indicate that motion parallax can be useful for absolute distance estimation, and they suggest that motion parallax would be useful in the underwater environment, where the usual sources of distance information are absent or distorted.
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paper_title: Vergence-accommodation conflicts hinder visual performance and cause visual fatigue.

paper_content:

Three-dimensional (3D) displays have become important for many applications including vision research, operation of remote devices, medical imaging, surgical training, scientific visualization, virtual prototyping, and more. In many of these applications, it is important for the graphic image to create a faithful impression of the 3D structure of the portrayed object or scene. Unfortunately, 3D displays often yield distortions in perceived 3D structure compared with the percepts of the real scenes the displays depict. A likely cause of such distortions is the fact that computer displays present images on one surface. Thus, focus cues-accommodation and blur in the retinal image-specify the depth of the display rather than the depths in the depicted scene. Additionally, the uncoupling of vergence and accommodation required by 3D displays frequently reduces one's ability to fuse the binocular stimulus and causes discomfort and fatigue for the viewer. We have developed a novel 3D display that presents focus cues that are correct or nearly correct for the depicted scene. We used this display to evaluate the influence of focus cues on perceptual distortions, fusion failures, and fatigue. We show that when focus cues are correct or nearly correct, (1) the time required to identify a stereoscopic stimulus is reduced, (2) stereoacuity in a time-limited task is increased, (3) distortions in perceived depth are reduced, and (4) viewer fatigue and discomfort are reduced. We discuss the implications of this work for vision research and the design and use of displays.
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paper_title: Effects of Stereo Viewing Conditions on Distance Perception in Virtual Environments

paper_content:

Several studies from different research groups investigating perception of absolute, egocentric distances in virtual environments have reported a compression of the intended size of the virtual space. One potential explanation for the compression is that inaccuracies and cue conflicts involving stereo viewing conditions in head mounted displays result in an inaccurate absolute scaling of the virtual world. We manipulate stereo viewing conditions in a head mounted display and show the effects of using both measured and fixed inter-pupilary distances, as well as bi-ocular and monocular viewing of graphics, on absolute distance judgments. Our results indicate that the amount of compression of distance judgments is unaffected by these manipulations. The equivalent performance with stereo, bi-ocular, and monocular viewing suggests that the limitations on the presentation of stereo imagery that are inherent in head mounted displays are likely not the source of distance compression reported in previous virtual environment studies.
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paper_title: Distance perception in NPR immersive virtual environments, revisited

paper_content:

Non-photorealistic rendering (NPR) is a representational technique that allows communicating the essence of a design while giving the viewer the sense that the design is open to change. Our research aims to address the question of how to effectively use non-photorealistic rendering in immersive virtual environments to enable the intuitive exploration of early architectural design concepts at full scale. Previous studies have shown that people typically underestimate egocentric distances in immersive virtual environments, regardless of rendering style, although we have recently found that distance estimation errors are minimized in the special case that the virtual environment is a high-fidelity replica of a real environment that the viewer is presently in or has recently been in. In this paper we re-examine the impact of rendering style on distance perception accuracy in this virtual environments context. Specifically, we report the results of an experiment that seeks to assess the accuracy with which people judge distances in a non-photorealistically rendered virtual environment that is a directly-derived stylistic abstraction of the actual environment that they are currently in. Our results indicate that people tend to underestimate distances to a significantly greater extent in a co-located virtual environment when it is rendered using a line-drawing style than when it is rendered using high fidelity textures derived from photographs.
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paper_title: Revisiting the effect of quality of graphics on distance judgments in virtual environments: A comparison of verbal reports and blind walking

paper_content:

In immersive virtual environments, judgments of perceived egocentric distance are significantly underestimated, as compared with accurate performance in the real world. Two experiments assessed the influence of graphics quality on two distinct estimates of distance, a visually directed walking task and verbal reports. Experiment 1 demonstrated a similar underestimation of distances walked to previously viewed targets in both low- and high-quality virtual classrooms. In Experiment 2, participants’ verbal judgments underestimated target distances in both graphics quality environments but were more accurate in the high-quality environment, consistent with the subjective impression that high-quality environments seem larger. Contrary to previous results, we suggest that quality of graphics does influence judgments of distance, but only for verbal reports. This behavioral dissociation has implications beyond the context of virtual environments and may reflect a differential use of cues and context for verbal reports and visually directed walking.
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paper_title: Perceived egocentric distances in real, image-based, and traditional virtual environments

paper_content:

In virtual environments, perceived egocentric distances are consistently underestimated when compared to the same distance judgments in the real world. The research presented in this paper explores two possible causes for the compressed distance perception in virtual environments: (1) real-time computer graphics rendering, and (2) immersive display technology. Our results show there is a significant difference in distance judgments between real and virtual environments. However, the differences between distance judgments in virtual photographic panorama environments and traditionally rendered virtual environments are small, suggesting that the display device is affecting distance judgments in virtual environments.
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paper_title: Does the Quality of the Computer Graphics Matter when Judging Distances in Visually Immersive Environments?

paper_content:

In the real world, people are quite accurate in judging distances to locations in the environment, at least for targets resting on the ground plane and distances out to about 20m. Distance judgments in visually immersive environments are much less accurate. Several studies have now shown that in visually immersive environments, the world appears significantly smaller than intended, This study investigates whether or not the compression in apparent distances is the result of the low-quality computer graphics utilized in previous investigations, Visually directed triangulated walking was used to assess distance judgments in the real world and in three virtual environments with graphical renderings of varying quality.
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paper_title: Perceiving layout and knowing distances: The integration, relative potency, and contextual use of different information about depth

paper_content:

Publisher Summary ::: This chapter discusses three questions: Why are there so many sources of information about layout? How is it that one perceives layout with near-metric accuracy when none of these sources yields metric information about it? Can one not do better, theoretically, in understanding the perception of layout than simply make a list? The answer to the first question begins with Todd's answer. Perceiving layout is extremely important to human beings, so important that it must be redundantly specified so that the redundancy can guard against the failure of any given source or the failure of any of the assumptions on which a given source is based. However, information redundancy is only part of the answer. Different sources of information about layout metrically reinforce and contrast with each other, providing a powerful network of constraints. The answer to the second proceeds from this idea. Through the analysis of depth-threshold functions for nine different sources of information about layout, one can begin to understand how those sources of information sharing the same-shaped functions across distances can help ramify judgments of layout by serving to correct measurement errors in each. Third, on the basis of the analyses and the pattern of functions, it suggests that list making has misled about space and layout. Psychologists and other vision scientists have generally considered layout, space, and distance as a uniform commodity in which observers carry out their day-to-day activities.
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paper_title: The influence of eye height and avatars on egocentric distance estimates in immersive virtual environments

paper_content:

It is well known that eye height is an important visual cue in the perception of apparent sizes and affordances in virtual environments. However, the influence of visual eye height on egocentric distances in virtual environments has received less attention. To explore this influence, we conducted an experiment where we manipulated the virtual eye height of the user in a head-mounted display virtual environment. As a measurement we asked the participants to verbally judge egocentric distances and to give verbal estimates of the dimensions of the virtual room. In addition, we provided the participants a self-animated avatar to investigate if this virtual self-representation has an impact on the accuracy of verbal distance judgments, as recently evidenced for distance judgments accessed with an action-based measure. When controlled for ownership, the avatar had a significant influence on the verbal estimates of egocentric distances as found in previous research. Interestingly, we found that the manipulation of eye height has a significant influence on the verbal estimates of both egocentric distances and the dimensions of the room. We discuss the implications which these research results have on those interested in space perception in both immersive virtual environments and the real world.
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paper_title: Distance Perception and the Visual Horizon in Head-Mounted Displays

paper_content:

Can distance perception be studied using virtual reality (VR) if distances are systematically underestimated in VR head-mounted displays (HMDs)? In an experiment in which a real environment was observed through an HMD, via live video, distances, as measured by visually directed walking, were underestimated even when the perceived environment was known to be real and present. However, the underestimation was linear, which means that higher-order space perception effects might be preserved in VR. This is illustrated in a second experiment, in which the visual horizon was artificially manipulated in a simulated outdoor field presented in immersive VR. As predicted by the claim that angle of declination from the horizon may serve as a strong cue to distance, lowering the horizon line produced “expansiv ” judgments of distance (power function exponents greater than one) both in verbal and in motor estimates.
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paper_title: Distance determined by the angular declination below the horizon.

paper_content:

A biological system is often more efficient when it takes advantage of the regularities in its environment. Like other terrestrial creatures, our spatial sense relies on the regularities associated with the ground surface. A simple, but important, ecological fact is that the field of view of the ground surface extends upwards from near (feet) to infinity (horizon). It forms the basis of a trigonometric relationship wherein the further an object on the ground is, the higher in the field of view it looks, with an object at infinity being seen at the horizon. Here, we provide support for the hypothesis that the visual system uses the angular declination below the horizon for distance judgement. Using a visually directed action task, we found that when the angular declination was increased by binocularly viewing through base-up prisms, the observer underestimated distance. After adapting to the same prisms, however, the observer overestimated distance on prism removal. Most significantly, we show that the distance overestimation as an after-effect of prism adaptation was due to a lowered perceived eye level, which reduced the object's angular declination below the horizon.
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paper_title: Minification affects verbal- and action-based distance judgments differently in head-mounted displays

paper_content:

Numerous studies report that people underestimate egocentric distances in Head-Mounted Display (HMD) virtual environments compared to real environments as measured by direct blind walking. Geometric minification, or rendering graphics with a larger field of view than the display's field of view, has been shown to eliminate this underestimation in a virtual hallway environment [Kuhl et al. 2006, 2009]. This study demonstrates that minification affects blind walking in a sparse classroom and does not influence verbal reports of distance. Since verbal reports of distance have been reported to be compressed in real environments, we speculate that minification in an HMD replicates peoples' real-world blind walking and verbal report distance judgments. We also demonstrate a new method for quantifying any unintentional miscalibration in our experiments. This process involves using the HMD in an augmented reality configuration and having each participant indicate where the targets and horizon appeared after each experiment. More work is necessary to understand how and why minification changes verbal- and walking-based egocentric distance judgments differently.
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paper_title: Human Factors Issues in Virtual Environments: A Review of the Literature

paper_content:

Virtual environments are envisioned as being systems that will enhance the communication between humans and computers. If virtual systems are to be effective and well received by their users, considerable human-factors research needs to be accomplished. This paper provides an overview of many of these human-factors issues, including human performance efficiency in virtual worlds (which is likely influenced by task characteristics, user characteristics, human sensory and motor physiology, multimodal interaction, and the potential need for new design metaphors); health and safety issues (of which cybersickness and deleterious physiological aftereffects may pose the most concern); and the social impact of the technology. The challenges each of these factors present to the effective design of virtual environments and systematic approaches to the resolution of each of these issues are discussed.
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paper_title: Image distortions in stereoscopic video systems

paper_content:

This paper discusses the origins, characteristics and effects of image distortions in stereoscopic video systems. The geometry of stereoscopic camera and display systems is presented first. This is followed by the analysis and diagrammatic presentation of various image distortions such as depth plane curvature, depth non-linearity, depth and size magnification, shearing distortion and keystone distortion. The variation of system parameters is also analysed with the help of plots of image geometry to show their effects on image distortions. The converged (toed-in) and parallel camera configurations are compared and the amount of vertical parallax induced by lens distortion and keystone distortion are discussed. The range of acceptable vertical parallax and the convergence/accommodation limitations on depth range are also discussed. It is shown that a number of these distortions can be eliminated by the appropriate choice of camera and display system parameters. There are some image distortions, however, which cannot be avoided due to the nature of human vision and limitations of current stereoscopic video display techniques.
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paper_title: Minification influences spatial judgments in virtual environments

paper_content:

Distances in immersive virtual environments (VEs) have been commonly reported as being spatially compressed while the same judgments are performed accurately in real space. Previous research has been unable to determine the cause of this spatial compression in VEs. The work reported here seeks to improve spatial judgments in VEs by manipulating the computer graphics in a way that biases distance judgments in a controlled manner, but is unnoticed by VE users. We show that shrinking the displayed image and appropriately rendering the scene to fill in the space resulting from shrinking the image ("minification") causes people to make more accurate distance judgments than they do with normally rendered graphics. Possible explanations for this effect include changes to the visual angle of declination from horizon to targets and changes in familiar size.
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paper_title: Perceptual issues in augmented reality

paper_content:

Between the extremes of real life and Virtual Reality lies the spectrum of Mixed Reality, in which views of the real world are combined in some proportion with views of a virtual environment. Combining direct view, stereoscopic video, and stereoscopic graphics, Augmented Reality describes that class of displays that consists primarily of a real environment, with graphic enhancements or augmentations. Augmented Virtuality describes that class of displays that enhance the virtual experience by adding elements of the real environment. All Mixed Reality systems are limited in their capability of accurately displaying and controlled all relevant depth cues, and as a result, perceptual biases can interfere with task performance. In this paper we identify and discuss eighteen issues that pertain to Mixed Reality in general, and Augmented Reality in particular.
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paper_title: Geometric Calibration of Head-Mounted Displays and its Effects on Distance Estimation

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Head-mounted displays (HMDs) allow users to observe virtual environments (VEs) from an egocentric perspective. However, several experiments have provided evidence that egocentric distances are perceived as compressed in VEs relative to the real world. Recent experiments suggest that the virtual view frustum set for rendering the VE has an essential impact on the user's estimation of distances. In this article we analyze if distance estimation can be improved by calibrating the view frustum for a given HMD and user. Unfortunately, in an immersive virtual reality (VR) environment, a full per user calibration is not trivial and manual per user adjustment often leads to mini- or magnification of the scene. Therefore, we propose a novel per user calibration approach with optical see-through displays commonly used in augmented reality (AR). This calibration takes advantage of a geometric scheme based on 2D point - 3D line correspondences, which can be used intuitively by inexperienced users and requires less than a minute to complete. The required user interaction is based on taking aim at a distant target marker with a close marker, which ensures non-planar measurements covering a large area of the interaction space while also reducing the number of required measurements to five. We found the tendency that a calibrated view frustum reduced the average distance underestimation of users in an immersive VR environment, but even the correctly calibrated view frustum could not entirely compensate for the distance underestimation effects.
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paper_title: Analyzing effects of geometric rendering parameters on size and distance estimation in on-axis stereographics

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Accurate perception of size and distance in a three-dimensional virtual environment is important for many applications. However, several experiments have revealed that spatial perception of virtual environments often deviates from the real world, even when the virtual scene is modeled as an accurate replica of a familiar physical environment. While previous research has elucidated various factors that can facilitate perceptual shifts, the effects of geometric rendering parameters on spatial cues are still not well understood. In this paper, we model and evaluate effects of spatial transformations caused by variations of the geometric field of view and the interpupillary distance in on-axis stereographic display environments. We evaluated different predictions in a psychophysical experiment in which subjects were asked to judge distance and size properties of virtual objects placed in a realistic virtual scene. Our results suggest that variations in the geometric field of view have a strong influence on distance judgments, whereas variations in the geometric interpupillary distance mainly affect size judgments.
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paper_title: Using texture maps to correct for optical distortion in head-mounted displays

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This paper describes a fast method of correcting for optical distortion in head-mounted displays (HMDs). Since the distorted display surface in an HMD is not rectilinear, the shape and location of the graphics window used with the display must be chosen carefully, and some corrections made to the predistortion model. A distortion correction might be performed with optics that reverse the distortion caused by HMD lenses, but such optics can be expensive and offer a correction for only one specific HMD. Integer incremental methods or a lookup table might be used to calculate the correction, but an I/O bottleneck makes this impractical in software. Instead, a texture map may be defined that approximates the required optical correction. Recent equipment advances allow undistorted images to be input into texture mapping hardware at interactive rates. Built in filtering handles predistortion aliasing artifacts.
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paper_title: Balancing fusion, image depth and distortion in stereoscopic head-tracked displays

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Abstract Stereoscopic display is a fundamental part of virtual reality HMDsystems and HTD (head-tracked display) systems such as thevirtual workbench and the CAVE. A common practice instereoscopic systems is deliberate incorrect modeling of user eyeseparation. Underestimating eye separation is frequentlynecessary for the human visual system to fuse stereo image pairsinto single 3D images, while overestimating eye separationenhances image depth. Unfortunately, false eye separationmodeling also distorts the perceived 3D image in undesirableways. This paper makes three fundamental contributions tounderstanding and controlling this stereo distortion. (1) Weanalyze the distortion using a new analytic description. Thisanalysis shows that even with perfect head tracking, a user willperceive virtual objects to warp and shift as she moves her head.(2) We present a new technique for counteracting the shearingcomponent of the distortion. (3) We present improved methodsfor managing image fusion problems for distant objects and forenhancing the depth of flat scenes.CR Categories and Subject Descriptions: I.3.7 [ComputerGraphics] Three-Dimensional Graphics and Realism - VirtualReality; I.3.6 [Computer Graphics] Methodology and Techniques– Ergonomics; I.3.6 [Computer Graphics] Methodology andTechniques – Interaction Techniques; I.3.3 [Computer Graphics]Picture/Image Generation – Viewing AlgorithmsAdditional Keywords: virtual reality, stereoscopic display,head-tracking, image distortion
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paper_title: A Computational Model for the Stereoscopic Optics of a Head-Mounted Display

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For stereoscopic photography or telepresence, orthostereoscopy occurs when the perceived size, shape, and relative position of objects in the three-dimensional scene being viewed match those of the physical objects in front of the camera. In virtual reality, the simulated scene has no physical counterpart, so orthostereoscopy must be defined in this case as constancy, as the head moves around, of the perceived size, shape, and relative positions of the simulated objects. ::: ::: Achieving this constancy requires that the computational model used to generate the graphics matches the physical geometry of the head-mounted display being used. This geometry includes the optics used to image the displays and the placement of the displays with respect to the eyes. The model may fail to match the geometry because model parameters are difficult to measure accurately, or because the model itself is in error. Two common modeling errors are ignoring the distortion caused by the optics and ignoring the variation in interpupillary distance across different users. ::: ::: A computational model for the geometry of a head-mounted display is presented, and the parameters of this model for the VPL EyePhone are calculated.
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paper_title: Effects of Stereo Viewing Conditions on Distance Perception in Virtual Environments

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Several studies from different research groups investigating perception of absolute, egocentric distances in virtual environments have reported a compression of the intended size of the virtual space. One potential explanation for the compression is that inaccuracies and cue conflicts involving stereo viewing conditions in head mounted displays result in an inaccurate absolute scaling of the virtual world. We manipulate stereo viewing conditions in a head mounted display and show the effects of using both measured and fixed inter-pupilary distances, as well as bi-ocular and monocular viewing of graphics, on absolute distance judgments. Our results indicate that the amount of compression of distance judgments is unaffected by these manipulations. The equivalent performance with stereo, bi-ocular, and monocular viewing suggests that the limitations on the presentation of stereo imagery that are inherent in head mounted displays are likely not the source of distance compression reported in previous virtual environment studies.
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paper_title: Surface textures improve the robustness of stereoscopic depth cues.

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This research develops design recommendations for surface textures (patterns of color on object surfaces) rendered with stereoscopic displays. In 3 method-of-adjustment procedure experiments, 8 participants matched the disparity of a circular probe and a planar stimulus rendered using a single visible edge. The experiments varied stimulus orientation and surface texture. Participants more accurately matched the depth of vertical stimuli than that of horizontal stimuli, consistent with previous studies and existing theory. Participants matched the depth of surfaces with large pixel-to-pixel luminance variations more accurately than they did surfaces with a small pixel-to-pixel luminance variation. Finally, they matched the depth of surfaces with vertical line patterns more accurately than they did surfaces with horizontal-striped texture patterns. These results suggest that designers can enhance depth perception in stereoscopic displays, and also reduce undesirable sensitivity to orientation, by rendering objects with surface textures using large pixel-to-pixel luminance variations.
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paper_title: Explaining the moon illusion

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An old explanation of the moon illusion holds that various cues place the horizon moon at an effectively greater distance than the elevated moon. Although both moons have the same angular size, the horizon moon must be perceived as larger. More recent explanations hold that differences in accommodation or other factors cause the elevated moon to appear smaller. As a result of this illusory difference in size, the elevated moon appears to be more distant than the horizon moon. These two explanations, both based on the geometry of stereopsis, lead to two diametrically opposed hypotheses. That is, a depth interval at a long distance is associated with a smaller binocular disparity, whereas an equal depth interval at a smaller distance is associated with a larger disparity. We conducted experiments involving artificial moons and confirmed the hypothesis that the horizon moon is at a greater perceptual distance. Moreover, when a moon of constant angular size was moved closer it was also perceived as growing smaller, which is consistent with the older explanation. Although Emmert's law does not predict the size-distance relationship over long distances, we conclude that the horizon moon is perceived as larger because the perceptual system treats it as though it is much farther away. Finally, we observe that recent explanations substitute perceived size for angular size as a cue to distance. Thus, they imply that perceptions cause perceptions.
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paper_title: Egocentric Distance Perception in a Virtual Environment Using a Perceptual Matching Task

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Objective: To determine whether egocentric distance judgments are accurate in a virtual environment using a perceptual matching task. Methods: Observers were immersed within a virtual environment consisting of an L-shaped room with a test object (a column) located down one corridor and a comparison object (a flagpole) located down the other. Perceived distances were measured by having the observers move the comparison object to match the distance to the test object. Textures in each corridor were independently varied, as was the size of the test object. Results: Significant effects were found for the texture pattern under the test object and for distance, but not for the texture under the comparison object or column size. Performance was best with a regular (brick) pattern. Overall, observers' judgments overestimated distance to the test object by approximately 7%. Conclusions: Egocentric distance judgments were relatively accurate compared to past research. Texture affected performance, with a regular pa...
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paper_title: Size-Constancy in the CAVE

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The use of virtual environments (VE) for many research and commercial purposes relies on its ability to generate environments that faithfully reproduce the physical world. However, due to its limitations the VE can have a number of flaws that adversely affect its use and believability. One of the more important aspects of this problem is whether the size of an object in the VE is perceived as it would be in the physical world. One of the fundamental phenomena for correct size is size-constancy, that is, an object is perceived to be the same size regardless of its distance from the observer. This is in spite of the fact that the retinal size of the object shrinks with increasing distance from the observer. We examined size-constancy in the CAVE and found that size-constancy is a strong and dominant perception in our subject population when the test object is accompanied by surrounding environmental objects. Furthermore, size-constancy changes to a visual angle performance (i.e., object size changed with distance from the subject) when these surrounding objects are removed from the scene. As previously described for the physical world, our results suggest that it is necessary to provide surrounding objects to aid in the determination of an object's depth and to elicit size-constancy in VE. These results are discussed regarding their implications for viewing objects in projection-based VE and the environments that play a role in the perception of object size in the CAVE.
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paper_title: Judging Perceived and Traversed Distance in Virtual Environments

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The ability to accurately estimate distance is an essential component of navigating large-scale spaces. Although the factors that influence distance estimation have been a topic of research in real-world environments for decades and are well known, research on distance estimation in virtual environments (VEs) has only just begun. Initial investigations of distance estimation in VEs suggest that observers are less accurate in estimating distance in VEs than in the real world (Lampton et al., 1995). Factors influencing distance estimates may be divided into those affecting perceived distance (visual cues only) and those affecting traversed distance to include visual, cognitive, and proprioceptive cues. To assess the contribution of the various distance cues in VEs, two experiments were conducted. The first required a static observer to estimate the distance to a cylinder placed at various points along a 130-foot hallway. This experiment examined the effects of floor texture, floor pattern, and object size on distance estimates in a VE. The second experiment required a moving observer to estimate route segment distances and total route distances along four routes, each totaling 1210 feet. This experiment assessed the effects of movement method, movement speed, compensatory cues, and wall texture density. Results indicate that observers underestimate distances both in VEs and in the real world, but the underestimates are more extreme in VEs. Texture did not reliably affect the distance estimates, providing no compensation for the gross underestimates of distance in VE. Traversing a distance improves the ability to estimate that distance, but more natural means of moving via a treadmill do not necessarily improve distance estimates over traditional methods of moving in VE (e.g., using a joystick). The addition of compensatory cues (tone every 10 feet traversed on alternate route segments) improves VE distance estimation to almost perfect performance.
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paper_title: Comparison of Two Indicators of Perceived Egocentric Distance Under Full-Cue and Reduced-Cue Conditions

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It has not been established that walking without vision to previewed targets is indeed controlled by perceived distance. To this end, we compared walking and verbal report as distance indicators, looking for a tight covariation in responses that would indicate control by a common variable. Targets from 79-500 cm away were presented under dark and well-lit conditions. Both verbal reports and walking indicated overestimation of near targets and underestimation of far targets under dark viewing conditions. Moreover, the finding that verbally reported distance plotted essentially as a single-valued function of walked distance and vice versa is evidence that both indicators were responding to the same internal variable, ostensibly perceived distance. In addition, binocular parallax, absolute motion parallax, and angular elevation were evaluated as distance cues, and only angular elevation exerted a large influence on perceived distance. When people are asked to view an object in a well-lit environment and then attempt to walk over to it with eyes closed, they do so, on average, without large systematic error. This finding has been documented by several researchers (Corlett, Patla, & Williams, 1985; Elliott, 1986,
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paper_title: Terrain influences the accurate judgement of distance

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Mathematically, three-dimensional space can be represented differently by the cartesian, polar, and other coordinate systems. However, in physical sciences, the choice of representation system is restricted by the need to simplify a machine's computation while enhancing its efficiency1. Does the brain, for the same reasons, ‘select’ the most cost-efficient way to represent the three-dimensional location of objects? As we frequentlyinteract with objects on the common ground surface, it might be beneficial for the visual system to code an object's location using a ground-surface-based reference frame2. More precisely, the brain could use a quasi-two-dimensional coordinate system (x s, y s) with respect to the ground surface (s), rather than a strictly three-dimensional coordinate system (x, y, z), thus reducing coding redundancy and simplifying computations2,3,4,5. Here we provide support for this view by studying human psychophysical performance in perceiving absolute distance and in visually directed action tasks6,7,8,9,10,11. For example, when an object was seen on a continuous, homogeneous texture ground surface, the observer judged the distance to the object accurately. However, when similar surface information was unavailable, for example, when the object was seen across a gap in the ground, or across distinct texture regions, distance judgement was impaired.
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paper_title: Judging Egocentric Distance on the Ground: Occlusion and Surface Integration

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On the basis of the finding that a common and homogeneous ground surface is vital for accurate egocentric distance judgments (Sinai et al, 1998 Nature395 497–500), we propose a sequential-surface-integration-process (SSIP) hypothesis to elucidate how the visual system constructs a representation of the ground-surface in the intermediate distance range. According to the SSIP hypothesis, a near ground-surface representation is formed from near depth cues, and is utilized as an anchor to integrate the more distant surfaces by using texture-gradient information as the depth cue. The SSIP hypothesis provides an explanation for the finding that egocentric distance judgment is underestimated when a texture boundary exists on the ground surface that commonly supports the observer and target. We tested the prediction that the fidelity of the visually represented ground-surface reference frame depends on how the visual system selects the surface information for integration. Specifically, if information is selected ...
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paper_title: Seeing beyond the target: Environmental context affects distance perception

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It is commonly assumed that perceived distance in full-cue, ecologically valid environments is redundantly specified and approximately veridical. However, recent research has called this assumption into question by demonstrating that distance perception varies in different types of environments even under full-cue viewing conditions. We report five experiments that demonstrate an effect of environmental context on perceived distance. We measured perceived distance in two types of environments (indoors and outdoors) with two types of measures (perceptual matching and blindwalking). We found effects of environmental context for both egocentric and exocentric distances. Across conditions, within individual experiments, all viewer-to-target depth-related variables were kept constant. The differences in perceived distance must therefore be explained by variations in the space beyond the target.
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paper_title: Estimation of distances in virtual environments using size constancy

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It is reported in the literature that distances from ::: the observer are underestimated more in virtual environments ::: (VEs) than in physical world conditions. On the other hand ::: estimation of size in VEs is quite accurate and follows a ::: size-constancy law when rich cues are present. This study ::: investigates how estimation of distance in a CAVETM ::: environment is affected by poor and rich cue conditions, subject ::: experience, and environmental learning when the position of the ::: objects is estimated using an experimental paradigm that ::: exploits size constancy. ::: A group of 18 healthy participants was asked to move a ::: virtual sphere controlled using the wand joystick to the position ::: where they thought a previously-displayed virtual cube ::: (stimulus) had appeared. Real-size physical models of the virtual ::: objects were also presented to the participants as a reference of ::: real physical distance during the trials. An accurate estimation ::: of distance implied that the participants assessed the relative size ::: of sphere and cube correctly. The cube appeared at depths ::: between 0.6 m and 3 m, measured along the depth direction of ::: the CAVE. The task was carried out in two environments: a ::: poor cue one with limited background cues, and a rich cue one ::: with textured background surfaces. ::: It was found that distances were underestimated in both poor ::: and rich cue conditions, with greater underestimation in the ::: poor cue environment. The analysis also indicated that factors ::: such as subject experience and environmental learning were not ::: influential. However, least square fitting of Stevens’ power law ::: indicated a high degree of accuracy during the estimation of ::: object locations. This accuracy was higher than in other studies ::: which were not based on a size-estimation paradigm. Thus as ::: indirect result, this study appears to show that accuracy when ::: estimating egocentric distances may be increased using an ::: experimental method that provides information on the relative ::: size of the objects used.
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paper_title: Depth Perception in Virtual Reality: Distance Estimations in Peri- and Extrapersonal Space

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ABSTRACT The present study investigated depth perception in virtual environments. Twenty-three participants verbally estimated ten distances between 40 cm and 500 cm in three different virtual environments in two conditions: (1) only one target was presented or (2) ten targets were presented at the same time. Additionally, the presence of a metric aid was varied. A questionnaire assessed subjective ratings about physical complaints (e.g., headache), the experience in the virtual world (e.g., presence), and the experiment itself (self-evaluation of the estimations). Results show that participants underestimate the virtual distances but are able to perceive the distances in the right metric order even when only very simple virtual environments are presented. Furthermore, interindividual differences and intraindividual stabilities can be found among participants, and neither the three different virtual environments nor the metric aid improved depth estimations. Estimation performance is better in peripersona...
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paper_title: Distance estimation in virtual and real environments using bisection

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Systematic error in judging distances in virtual environments is one of the most interesting problems in perceptual studies of virtual environments. The causes of this error are not known. This paper presents an experiment designed to investigate distance perception in virtual environments using the method of distance bisection (fractionation). Most other studies of distance perception in virtual environment rely on measures involving motor responses or time judgments. Unlike these, the method used in this study depends purely on visually perceived distances. Our experiment compares distance bisection judgments in virtual environments, bisection judgments in the real-world, and bisection judgments in the real-world with limited field of view. We also perform the judgments in two environmental contexts, an outdoor environment and an indoor environment. We find evidence that nonlinear distance compression occurs in virtual environments, but judgments in real-world conditions are accurate. We do not find an effect of environmental context.
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paper_title: Accommodation and Size-Constancy of Virtual Objects

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Accommodation has been suspected as a contributor to size illusions in virtual environments (VE) due to the lack of appropriate accommodative stimuli in a VE for the objects displayed. Previous experiments examining size-constancy in VE have shown that monocular cues to depth that accompany the object are a major contributor to correct size perception. When these accompanying cues are removed perceived size varied with the object's distance from the subject, i.e., visual angle. If accommodation were the dominant mechanism contributing to a visual angle response [due to its action to keep physical objects clear] in this condition, an open-loop accommodation viewing condition might restore size-constancy to this condition. Pinhole apertures were used to open-loop accommodation and examine if size-constancy might be restored when few accompanying monocular cues to depth were present. Visual angle performance when viewing a low cue environment was found with and without the use of the pinhole apertures. Thus, these results signify that accommodation does not play a dominate role in the loss of size-constancy in sparse visual environments often used in VE. These results suggest that size-constancy is driven by the inclusion of the remaining monocular cues to depth in VE as it is in the physical world.
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paper_title: On the Determinants of Size-Constancy in a Virtual Environment

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—An important aspect of a subject’s perception of ::: virtual objects in a virtual environment is whether the size of the ::: object is perceived as it would be in the physical world, which is ::: named size-constancy. The ability of subjects to appreciate ::: size-constancy in an immersive virtual environment was studied ::: while scene complexity, stereovision and motion parallax visual ::: factors were manipulated resulting in twelve different viewing ::: conditions. Under each visual condition, 18 subjects made size ::: judgments of a virtual object displayed at five different distances ::: from them. Responses from the majority of our population ::: demonstrated that scene complexity and stereovision have a ::: significant impact on subjects’ ability to appreciate size-constancy. ::: In contrast, motion parallax produced by moving the virtual ::: environment or by the movements of the observer alone proved ::: not to be a significant factor in determining size-constancy ::: performance. Consequently, size-constancy is best obtained when ::: scene complexity and stereovision are components of the viewing ::: conditions.
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paper_title: Environmental context influences visually perceived distance

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What properties determine visually perceived space? We discovered that the perceived relative distances of familiar objects in natural settings depended in unexpected ways on the surrounding visual field. Observers bisected egocentric distances in a lobby, in a hallway, and on an open lawn. Three key findings were the following: (1) Perceived midpoints were too far from the observer, which is the opposite of the common foreshortening effect. (2) Thisantiforeshortening constant error depended on the environmental setting — greatest in the lobby and hall but nonsignificant on the lawn. (3) Context also affected distance discrimination; variability was greater in the hall than in the lobby or on the lawn. A second experiment replicated these findings, using a method of constant stimuli. Evidently, both the accuracy and the precision of perceived distance depend on subtle properties of the surrounding environment.
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paper_title: Perceiving distance accurately by a directional process of integrating ground information

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By itself, the absolute distance of an object cannot be accurately judged beyond 2–3 m (refs 1–3). Yet, when it is viewed with reference to a flat terrain, humans accurately judge the absolute distance of the object up to 20 m, an ability that is important for various actions4,5,6,7,8. Here we provide evidence that this is accomplished by integrating local patches of ground information into a global surface reference frame. We first show that restricting an observer's visual field of view to the local ground area around the target leads to distance underestimation, indicating that a relatively wide expanse of the ground surface is required for accurate distance judgement. Second, as proof of surface integration, we show that even with the restricted view, the observer can accurately judge absolute distance by scanning local patches of the ground surface, bit by bit, from near to far, but not in the reverse direction. This finding also reveals that the surface integration process uses the near-ground-surface information as a foundation for surface representation, and extrapolation to the far ground surface around the target for accurate absolute distance computation.
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paper_title: The influence of eye height and avatars on egocentric distance estimates in immersive virtual environments

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It is well known that eye height is an important visual cue in the perception of apparent sizes and affordances in virtual environments. However, the influence of visual eye height on egocentric distances in virtual environments has received less attention. To explore this influence, we conducted an experiment where we manipulated the virtual eye height of the user in a head-mounted display virtual environment. As a measurement we asked the participants to verbally judge egocentric distances and to give verbal estimates of the dimensions of the virtual room. In addition, we provided the participants a self-animated avatar to investigate if this virtual self-representation has an impact on the accuracy of verbal distance judgments, as recently evidenced for distance judgments accessed with an action-based measure. When controlled for ownership, the avatar had a significant influence on the verbal estimates of egocentric distances as found in previous research. Interestingly, we found that the manipulation of eye height has a significant influence on the verbal estimates of both egocentric distances and the dimensions of the room. We discuss the implications which these research results have on those interested in space perception in both immersive virtual environments and the real world.
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paper_title: The influence of avatar (self and character) animations on distance estimation, object interaction and locomotion in immersive virtual environments

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Humans have been shown to perceive and perform actions differently in immersive virtual environments (VEs) as compared to the real world. Immersive VEs often lack the presence of virtual characters; users are rarely presented with a representation of their own body and have little to no experience with other human avatars/characters. However, virtual characters and avatars are more often being used in immersive VEs. In a two-phase experiment, we investigated the impact of seeing an animated character or a self-avatar in a head-mounted display VE on task performance. In particular, we examined performance on three different behavioral tasks in the VE. In a learning phase, participants either saw a character animation or an animation of a cone. In the task performance phase, we varied whether participants saw a co-located animated self-avatar. Participants performed a distance estimation, an object interaction and a stepping stone locomotion task within the VE. We find no impact of a character animation or a self-avatar on distance estimates. We find that both the animation and the self-avatar influenced task performance which involved interaction with elements in the environment; the object interaction and the stepping stone tasks. Overall the participants performed the tasks faster and more accurately when they either had a self-avatar or saw a character animation. The results suggest that including character animations or self-avatars before or during task execution is beneficial to performance on some common interaction tasks within the VE. Finally, we see that in all cases (even without seeing a character or self-avatar animation) participants learned to perform the tasks more quickly and/or more accurately over time.
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paper_title: A full-body avatar improves egocentric distance judgments in an immersive virtual environment

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A number of investigators have reported that distance judgments in virtual environments (VEs) are systematically smaller than distance judgments made in comparably-sized real environments. Many variables that may contribute to this difference have been investigated but none of them fully explain the distance compression. In this paper we asked whether seeing a fully-articulated visual representation of oneself (avatar) within a virtual environment would lead to more accurate estimations of distance. We found that participants who explored near space without the visual avatar underestimated egocentric distance judgments compared to those who similarly explored near space while viewing a fully-articulated avatar. These results are discussed with respect to the perceptual and cognitive mechanisms that may be involved in the observed effects as well as the benefits of visual feedback in the form of an avatar for VE applications.
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paper_title: The effects of virtual character animation on spatial judgments

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Inaccurate perception of distances is a known problem within virtual environments. We hypothesize that the inclusion of virtual characters within these environments can improve an observer's ability to judge distances and achieve accurate spatial understanding. We have conducted an empirical study using a desktop display of a small scale environment to evaluate the validity of this concept. We investigated whether the presence and quantity of virtual human characters, as well as the naturalness of their locomotion animations, could improve egocentric and exocentric distance estimations. Preliminary results suggest that static or properly animated characters could improve exocentric estimations, and properly animated characters could reduce egocentric distance compression errors.
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paper_title: Egocentric distance perception in real and HMD-based virtual environments: the effect of limited scanning method

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We conducted four experiments on egocentric depth perception using blind walking with a restricted scanning method in both the real and a virtual environment. Our viewing condition in all experiments was monocular. We varied the field of view (real), scan direction (real), blind walking method (real and virtual), and self-representation (virtual) over distances of 4 meters to 7 meters. The field of view varied between 21.1° and 13.6°. The scan direction varied between near-to-far scanning and far-to-near scanning. The blind walking method varied between direct blind walking and an indirect method of blind walking that matched the geometry of our laboratory. We varied self-representation between having a self-avatar (a fully tracked, animated, and first-person perspective of the user), having a static avatar (a mannequin avatar that did not move), to having no avatar (a disembodied camera view of the virtual environment). In the real environment, we find an effect of field of view; participants performed more accurately with larger field of view. In both real and virtual environments, we find an effect of blind walking method; participants performed more accurately in direct blind walking. We do not find an effect of distance underestimation in any environment, nor do we find an effect of self-representation.
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paper_title: Avatar self-embodiment enhances distance perception accuracy in non-photorealistic immersive virtual environments

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Non-photorealistically rendered (NPR) immersive virtual environments (IVEs) can facilitate conceptual design in architecture by enabling preliminary design sketches to be previewed and experienced at full scale, from a first-person perspective. However, it is critical to ensure the accurate spatial perception of the represented information, and many studies have shown that people typically underestimate distances in most IVEs, regardless of rendering style. In previous work we have found that while people tend to judge distances more accurately in an IVE that is a high-fidelity replica of their concurrently occupied real environment than in an IVE that it is a photorealistic representation of a real place that they've never been to, significant distance estimation errors re-emerge when the replica environment is represented in a NPR style. We have also previously found that distance estimation accuracy can be improved, in photo-realistically rendered novel virtual environments, when people are given a fully tracked, high fidelity first person avatar self-embodiment. In this paper we report the results of an experiment that seeks to determine whether providing users with a high-fidelity avatar self-embodiment in a NPR virtual replica environment will enable them to perceive the 3D spatial layout of that environment more accurately. We find that users who are given a first person avatar in an NPR replica environment judge distances more accurately than do users who experience the NPR replica room without an embodiment, but not as accurately as users whose distance judgments are made in a photorealistically rendered virtual replica room. Our results provide a partial solution to the problem of facilitating accurate distance perception in NPR virtual environments, while supporting and expanding the scope of previous findings that giving people a realistic avatar self-embodiment in an IVE can help them to interpret what they see through an HMD in a way that is more similar to how they would interpret a corresponding visual stimulus in the real world.
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paper_title: Analyzing the effect of a virtual avatar's geometric and motion fidelity on ego-centric spatial perception in immersive virtual environments

paper_content:

Previous work has shown that giving a user a first-person virtual avatar can increase the accuracy of their egocentric distance judgments in an immersive virtual environment (IVE). This result provides one of the rare examples of a manipulation that can enable improved spatial task performance in a virtual environment without potentially compromising the ability for accurate information transfer to the real world. However, many open questions about the scope and limitations of the effectiveness of IVE avatar self-embodiment remain. In this paper, we report the results of a series of four experiments, involving a total of 40 participants, that explore the importance, to the desired outcome of enabling enhanced spatial perception accuracy, of providing a high level of geometric and motion fidelity in the avatar representation. In these studies, we assess participants' abilities to estimate egocentric distances in a novel virtual environment under four different conditions of avatar self-embodiment: a) no avatar; b) a fully tracked, custom-fitted, high fidelity avatar, represented using a textured triangle mesh; c) the same avatar as in b) but implemented with single point rather than full body tracking; and d) a fully tracked but simplified avatar, represented by a collection of small spheres at the raw tracking marker locations. The goal of these investigations is to attain insight into what specific characteristics of a virtual avatar representation are most important to facilitating accurate spatial perception, and what cost-saving measures in the avatar implementation might be possible. Our results indicate that each of the simplified avatar implementations we tested is significantly less effective than the full avatar in facilitating accurate distance estimation; in fact, the participants who were given the simplified avatar representations performed only marginally (but not significantly) more accurately than the participants who were given no avatar at all. These findings suggest that the beneficial impact of providing users with a high fidelity avatar self-representation may stem less directly from the low-level size and motion cues that the avatar embodiment makes available to them than from the cognitive sense of presence that the self-embodiment supports.
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paper_title: Parasocial Interaction with My Avatar: Effects of Interdependent Self-Construal and the Mediating Role of Self-Presence in an Avatar-Based Console Game, Wii

paper_content:

Abstract The “self” concept has grown increasingly important in interactive media environments. This study investigated self-related processes in an avatar-based game console, Wii. A key feature of the Wii is its motion-sensing capability that empowers players to manipulate and interact with items on-screen via movement. The present study examined the effects of video game players' self-construal on parasocial interaction with their avatars and feelings of self-presence. In this study, parasocial interaction was operationally defined as the extent of game players' interpersonal involvement with their avatar and the extent to which game players perceive themselves as interacting with the avatar. Self-presence was defined as the degree to which video game players feel as if their avatar on the screen were their real self. Based on an experiment, the study discovered that game players with high interdependent self-construal showed closer parasocial interaction and higher level of self-presence than those wit...
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paper_title: Exploring Self-Presence in Collaborative Virtual Teams

paper_content:

The concept of self-presence provides a framework for understanding how people connect to virtual self-representations on three distinct levels (body, emotions, and identity). The present study aims to build on previous support for the reliability and construct validity of this framework. Participants (N=81) who used avatars in a semester-long collaborative virtual group project were examined. A factor analysis of the Self-Presence Questionnaire (SPQ) was mostly consistent with the framework of self-presence, though a new sub-factor emerged, possibly due to new SPQ items or limitations of the virtual environment. Factors of self-presence were related to social presence as expected, but not to frequency of avatar changes. These findings support the framework, but deeper explorations of the concept are still necessary.
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paper_title: The Effect of Viewing a Self-Avatar on Distance Judgments in an HMD-Based Virtual Environment

paper_content:

Few HMD-based virtual environment systems display a rendering of the user's own body. Subjectively, this often leads to a sense of disembodiment in the virtual world. We explore the effect of being able to see one's own body in such systems on an objective measure of the accuracy of one form of space perception. Using an action-based response measure, we found that participants who explored near space while seeing a fully-articulated and tracked visual representation of themselves subsequently made more accurate judgments of absolute egocentric distance to locations ranging from 4 m to 6 m away from where they were standing than did participants who saw no avatar. A nonanimated avatar also improved distance judgments, but by a lesser amount. Participants who viewed either animated or static avatars positioned 3 m in front of their own position made subsequent distance judgments with similar accuracy to the participants who viewed the equivalent animated or static avatar positioned at their own location. We discuss the implications of these results on theories of embodied perception in virtual environments.
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paper_title: Correlations Between Physiological Response, Gait, Personality, and Presence in Immersive Virtual Environments

paper_content:

In previous work, we have found significant differences in the accuracy with which people make initial spatial judgments in different types of head-mounted, display-based immersive virtual environments (IVEs; Phillips, Interrante, Kaeding, Ries, & Anderson, 2010). In particular, we have found that people tend to less severely underestimate egocentric distances in a virtual environment that is a photorealistic replica of a real place that they have recently visited than when the virtual environment is either a photorealistic replica of an unfamiliar place, or a nonphotorealistically (NPR) portrayed version of a familiar space. We have also noted significant differences in the effect of environment type on distance perception accuracy between individual participants. In this paper, we report the results of two experiments that seek further insight into these phenomena, focusing on factors related to depth of presence in the virtual environment. In our reported first experiment, we immersed users (between-subjects) in one of the three different types of IVEs and asked them to perform a series of well-defined tasks along a delimited path, first in a control version of the environment, and then in a stressful variant in which the floor around the marked path was cut away to reveal a 20-ft drop. We assessed participants' sense of presence during each trial using a diverse set of measures, including: questionnaires, recordings of heart rate and galvanic skin response, and gait metrics derived from tracking data. We computed the differences in each of these measures between the stressful and nonstressful versions of each environment, and then compared the changes due to stress between the different virtual environment conditions. Pooling the data over all participants in each group, we found significant physiological indications of stress after the appearance of the pit in all three environments, but we did not find significant differences in the magnitude of the stress response between the different virtual environment locales. We also did not find any significant difference in the level of subjective presence reported in each environment. However, we did find significant differences in gait: participants in the photorealistic replica room showed a significantly greater reduction in stride speed and stride length between the control and pit version of the room than did participants in either the photorealistically rendered nonreplica environment or the NPR replica environment conditions. Our second experiment, conducted with a new set of participants, sought to more directly investigate potential correlations between distance estimation accuracy and personality, stress response, and reported sense of presence, comparatively across different immersive virtual environment conditions. We used pretest questionnaires to assess a variety of personality measures, and then randomly immersed participants (between-subjects) in either the photorealistic replica or photorealistic non-replica environment and assessed the accuracy of their egocentric distance judgments in that IVE, followed by control trials in a neutral, real-world location. We then had participants go through the same set of tasks as in our first experiment while we collected physiological measures of their stress level and tracked their gait, and we compared the changes in these measures between the neutral and pit-enhanced versions of the environment. Finally, we had people fill out a brief presence questionnaire.Analyzing all of these data, we found that participants made significantly greater distance estimation errors in the unfamiliar room environment than in the replica room environment, but no other differences between the two environments were significant. We found significant positive correlation between several of the personality measures, but we did not find any notable significant correlations between personality and presence, or between either personality or presence and gait changes or distance estimation accuracy. These results suggest to us that the relationship between personality, presence, and performance in IVEs is complicated and not easily captured by existing measures.
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paper_title: Distance perception in NPR immersive virtual environments, revisited

paper_content:

Non-photorealistic rendering (NPR) is a representational technique that allows communicating the essence of a design while giving the viewer the sense that the design is open to change. Our research aims to address the question of how to effectively use non-photorealistic rendering in immersive virtual environments to enable the intuitive exploration of early architectural design concepts at full scale. Previous studies have shown that people typically underestimate egocentric distances in immersive virtual environments, regardless of rendering style, although we have recently found that distance estimation errors are minimized in the special case that the virtual environment is a high-fidelity replica of a real environment that the viewer is presently in or has recently been in. In this paper we re-examine the impact of rendering style on distance perception accuracy in this virtual environments context. Specifically, we report the results of an experiment that seeks to assess the accuracy with which people judge distances in a non-photorealistically rendered virtual environment that is a directly-derived stylistic abstraction of the actual environment that they are currently in. Our results indicate that people tend to underestimate distances to a significantly greater extent in a co-located virtual environment when it is rendered using a line-drawing style than when it is rendered using high fidelity textures derived from photographs.
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paper_title: Perceiving layout and knowing distances: The integration, relative potency, and contextual use of different information about depth

paper_content:

Publisher Summary ::: This chapter discusses three questions: Why are there so many sources of information about layout? How is it that one perceives layout with near-metric accuracy when none of these sources yields metric information about it? Can one not do better, theoretically, in understanding the perception of layout than simply make a list? The answer to the first question begins with Todd's answer. Perceiving layout is extremely important to human beings, so important that it must be redundantly specified so that the redundancy can guard against the failure of any given source or the failure of any of the assumptions on which a given source is based. However, information redundancy is only part of the answer. Different sources of information about layout metrically reinforce and contrast with each other, providing a powerful network of constraints. The answer to the second proceeds from this idea. Through the analysis of depth-threshold functions for nine different sources of information about layout, one can begin to understand how those sources of information sharing the same-shaped functions across distances can help ramify judgments of layout by serving to correct measurement errors in each. Third, on the basis of the analyses and the pattern of functions, it suggests that list making has misled about space and layout. Psychologists and other vision scientists have generally considered layout, space, and distance as a uniform commodity in which observers carry out their day-to-day activities.
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paper_title: Absolute motion parallax weakly determines visual scale in real and virtual environments

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The determinants of visual scale (size and distance) under monocular viewing are still largely unknown. The problem of visual scale under monocular viewing becomes readily apparent when one moves about within a virtual environment. It might be thought that the absolute motion parallax of stationary objects (both in real and virtual environments), under the assumption of the stationarity, would immediately determine their apparent size and distance for an observer who is walking about. We sought to assess the effectiveness of observer- produced motion parallax in scaling apparent size and distance within near space. We had subjects judge the apparent size and distance of real and virtual objects under closely matched conditions Real and virtual targets were 4 spheres seen in darkness at eye level. the targets ranges in diameter from 3.7 cm to 14.8 cm and were viewed monocularly from difference distances, with a subset of the size/distance combinations resulting in projectively equivalent stimuli at the viewing origin. subjects moved laterally plus and minus 1 m to produce large amounts of motion parallax. when angular size was held constant and motion parallax acted as a differential cue to target size and distance, judged size varied by a facto or 1.67 and 1.18 for the real and virtual environments, respectively, well short of the fourfold change in distal size. Similarly, distance judgments varied by factors of only 1.74 and 1.07 respectively. We conclude that absolute motion parallax only weakly determines the visual scale of nearby objects varying over a fourfold range in size.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
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paper_title: Depth Perception in Virtual Reality: Distance Estimations in Peri- and Extrapersonal Space

paper_content:

ABSTRACT The present study investigated depth perception in virtual environments. Twenty-three participants verbally estimated ten distances between 40 cm and 500 cm in three different virtual environments in two conditions: (1) only one target was presented or (2) ten targets were presented at the same time. Additionally, the presence of a metric aid was varied. A questionnaire assessed subjective ratings about physical complaints (e.g., headache), the experience in the virtual world (e.g., presence), and the experiment itself (self-evaluation of the estimations). Results show that participants underestimate the virtual distances but are able to perceive the distances in the right metric order even when only very simple virtual environments are presented. Furthermore, interindividual differences and intraindividual stabilities can be found among participants, and neither the three different virtual environments nor the metric aid improved depth estimations. Estimation performance is better in peripersona...
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paper_title: Elucidating Factors that Can Facilitate Veridical Spatial Perception in Immersive Virtual Environments

paper_content:

Ensuring veridical spatial perception in immersive virtual environments (IVEs) is an important yet elusive goal. In this paper, we present the results of two experiments that seek further insight into this problem. In the first of these experiments, initially reported in Interrante, Ries, Lindquist, and Anderson (2007), we seek to disambiguate two alternative hypotheses that could explain our recent finding (Interrante, Anderson, and Ries, 2006a) that participants appear not to significantly underestimate egocentric distances in HMD-based IVEs, relative to in the real world, in the special case that they unambiguously know, through first-hand observation, that the presented virtual environment is a high-fidelity 3D model of their concurrently occupied real environment. Specifically, we seek to determine whether people are able to make similarly veridical judgments of egocentric distances in these matched real and virtual environments because (1) they are able to use metric information gleaned from their exposure to the real environment to calibrate their judgments of sizes and distances in the matched virtual environment, or because (2) their prior exposure to the real environment enabled them to achieve a heightened sense of presence in the matched virtual environment, which leads them to act on the visual stimulus provided through the HMD as if they were interpreting it as a computer-mediated view of an actual real environment, rather than just as a computer-generated picture, with all of the uncertainties that that would imply. In our second experiment, we seek to investigate the extent to which augmenting a virtual environment model with faithfully-modeled replicas of familiar objects might enhance people's ability to make accurate judgments of egocentric distances in that environment.
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paper_title: Distance perception in NPR immersive virtual environments, revisited

paper_content:

Non-photorealistic rendering (NPR) is a representational technique that allows communicating the essence of a design while giving the viewer the sense that the design is open to change. Our research aims to address the question of how to effectively use non-photorealistic rendering in immersive virtual environments to enable the intuitive exploration of early architectural design concepts at full scale. Previous studies have shown that people typically underestimate egocentric distances in immersive virtual environments, regardless of rendering style, although we have recently found that distance estimation errors are minimized in the special case that the virtual environment is a high-fidelity replica of a real environment that the viewer is presently in or has recently been in. In this paper we re-examine the impact of rendering style on distance perception accuracy in this virtual environments context. Specifically, we report the results of an experiment that seeks to assess the accuracy with which people judge distances in a non-photorealistically rendered virtual environment that is a directly-derived stylistic abstraction of the actual environment that they are currently in. Our results indicate that people tend to underestimate distances to a significantly greater extent in a co-located virtual environment when it is rendered using a line-drawing style than when it is rendered using high fidelity textures derived from photographs.
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paper_title: Peripheral visual information and its effect on distance judgments in virtual and augmented environments

paper_content:

A frequently observed problem in medium-field virtual environments is the underestimation of egocentric depth. This problem has been described numerous times and with widely varying degrees of severity, and although there has been considerable progress made in modifying observer behavior to compensate for these misperceptions, the question of why these errors exist is still an open issue. This paper presents the findings of a series of experiments, comprising 103 participants, that attempts to identify and quantify the source of a pattern of adaptation and improved depth judgment accuracy over time scales of less than one hour. Taken together, these experiments suggest that peripheral visual information is an important source of information for the calibration of movement within medium-field virtual environments.
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paper_title: The Effect Of Feedback Training On Distance Estimation In Virtual Environments

paper_content:

It is often noted that distances are significantly underestimated in computer-simulated (virtual) environments. Two experiments examine observers' ability to use error corrective feedback to improve the accuracy of judgments of egocentric and exocentric distances. In Experiment 1, observers viewed objects in an immersive virtual environment and estimated their distance through a blindfolded walking task. Different groups received feedback on either egocentric, exocentric or none of these judgments. Receiving feedback improved observers' ability to estimate only those distances for which feedback was provided. These effects persisted for at least 1 week. In Experiment 2, observers estimated egocentric distance by means of both a direct and indirect walking task. Receiving feedback on the direct walking task predominantly improved direct estimates and not indirect estimates. These findings suggest that although feedback training offers a relatively straightforward and immediate way of overcoming problems of distance estimation, its effects are specific to both the type of judgment and the type of response. Copyright © 2005 John Wiley & Sons, Ltd.
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paper_title: The influence of feedback on egocentric distance judgments in real and virtual environments

paper_content:

A number of investigators have reported that distance judgments in virtual environments (VEs) are systematically smaller than distance judgments made in comparably-sized real environments. Many variables that may contribute to this difference have been investigated but none of them fully explain the distance compression. One approach to this problem that has implications for both VE applications and the study of perceptual mechanisms is to examine the influence of the feedback available to the user. Most generally, we asked whether feedback within a virtual environment would lead to more accurate estimations of distance. Next, given the prediction that some change in behavior would be observed, we asked whether specific adaptation effects would generalize to other indications of distance. Finally, we asked whether these effects would transfer from the VE to the real world. All distance judgments in the head-mounted display (HMD) became near accurate after three different forms of feedback were given within the HMD. However, not all feedback sessions within the HMD altered real world distance judgments. These results are discussed with respect to the perceptual and cognitive mechanisms that may be involved in the observed adaptation effects as well as the benefits of feedback for VE applications.
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paper_title: Effects of calibration to visual and haptic feedback on near-field depth perception in an immersive virtual environment

paper_content:

Distances are regularly underestimated in immersive virtual environments (IVEs) [Witmer and Kline 1998; Loomis and Knapp 2003]. Few experiments, however, have examined the ability of calibration to overcome distortions of depth perception in IVEs. This experiment is designed to examine the effect of calibration via haptic and visual feedback on distance estimates in an IVE. Participants provided verbal and physical reach responses to target distances presented during three sessions; a baseline measure without feedback, a calibration session with visual and haptic feedback, and finally a post-calibration session without feedback. Feedback was shown to calibrate distance estimates within an IVE. Discussion focused on the possibility that costly solutions and research endeavors seeking to remedy the compression of distances may become less necessary if users are simply given the opportunity to use manual activity to calibrate to the IVE.
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paper_title: Interaction with an immersive virtual environment corrects users' distance estimates.

paper_content:

OBJECTIVE ::: Two experiments examined whether prior interaction within an immersive virtual environment (VE) enabled people to improve the accuracy of their distance judgments and whether an improved ability to estimate distance generalized to other means of estimating distances. ::: ::: ::: BACKGROUND ::: Prior literature has consistently found that users of immersive VEs underestimate distances by approximately 50%. ::: ::: ::: METHOD ::: In each of the two experiments, 16 participants viewed objects in an immersive VE and estimated their distance to them by means of blindfolded walking tasks before and after interacting with the VE. ::: ::: ::: RESULTS ::: The interaction task significantly corrected users' underestimation bias to nearly veridical. Differences between pre- and post-interaction mean distance estimation accuracy were large (d = 4.63), and significant (p < .001), and they generalized across response task. ::: ::: ::: CONCLUSION ::: This finding limits the generality of the underestimation effect in VEs and suggests that distance underestimation in VEs may not be a road block to the development of VE applications. ::: ::: ::: APPLICATION ::: Potential or actual applications of this research include the improvement of VE systems requiring accurate spatial awareness.
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paper_title: The influence of avatar (self and character) animations on distance estimation, object interaction and locomotion in immersive virtual environments

paper_content:

Humans have been shown to perceive and perform actions differently in immersive virtual environments (VEs) as compared to the real world. Immersive VEs often lack the presence of virtual characters; users are rarely presented with a representation of their own body and have little to no experience with other human avatars/characters. However, virtual characters and avatars are more often being used in immersive VEs. In a two-phase experiment, we investigated the impact of seeing an animated character or a self-avatar in a head-mounted display VE on task performance. In particular, we examined performance on three different behavioral tasks in the VE. In a learning phase, participants either saw a character animation or an animation of a cone. In the task performance phase, we varied whether participants saw a co-located animated self-avatar. Participants performed a distance estimation, an object interaction and a stepping stone locomotion task within the VE. We find no impact of a character animation or a self-avatar on distance estimates. We find that both the animation and the self-avatar influenced task performance which involved interaction with elements in the environment; the object interaction and the stepping stone tasks. Overall the participants performed the tasks faster and more accurately when they either had a self-avatar or saw a character animation. The results suggest that including character animations or self-avatars before or during task execution is beneficial to performance on some common interaction tasks within the VE. Finally, we see that in all cases (even without seeing a character or self-avatar animation) participants learned to perform the tasks more quickly and/or more accurately over time.
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paper_title: Vision without inversion of the retinal image.

paper_content:

Seventh Day.—In the morning the flow of ideas while I was blindfolded was like that described for the evening before. But I noticed in bathing that the old representation of those parts of my body which I had so frequently seen ( at least in their clothing) during the experiment, was decidedly less vivid, the outline more blurred, the color paler, grayer, more ' washed out,' than of the parts which had never come within the limits of the visual field. Later, with my lenses on, it seemed at first as if the experience was in all respects the same as on the previous day. But when I began to pace rapidly up and down the room, I felt that I was more at home in the scene than ever before. There was perfect reality in my visual surroundings, and I gave myself up to them without reserve and without being conscious of a single note of discord with what I saw. This feeling of complete harmony throughout, lasted as long as I kept my legs either within or near the borders of my field of view. Otherwise the older, inappropriate representation of my body arose at times, but faded, while the new representation revived, as soon as some passing object was seen to enter the region into which the older image of my body extended. The absence of any tactual experiences such as a real body in that position would imply, cast, for the moment, an illusory character over the older form of representation. To what extent objects in view suggested the idea of other things in harmonious relation with the seen things is best shown by the following cases: As I walked into my bedroom and saw the bedstead, I involuntarily thought of the windows, repre1 Concluded.
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paper_title: Throwing while looking through prisms. II. Specificity and storage of multiple gaze-throw calibrations.

paper_content:

Summary Human subjects threw balls of clay at a visual target while looking through wedge prism spectacles. In studies of short-term adjustment, subjects threw in the direction of their prism-bent gaze, missing the target to that side. Within 10–30 throws, they gradually adapted with a wider gaze-throw angle and hit the target. Immediately after removal of the prisms the wide gaze-throw angle persisted and throws missed the target to the opposite side, the so-called ‘negative after-effect’. Repeated throws were required to adapt back to the normal gaze-throw angle and hit the target. The adaptation was specific both to the body parts trained and the type of throw trained: training with the right hand did not generalize to throwing with the left; overhand training seldom generalized to underhand throwing. In a study of long-term adjustment, two subjects threw with the same hand (right) and the same type of throw (overhand) alternately, with and without prisms, over a period of 6 weeks. They gradually learned to hit the target on the first throw, with and without prisms. The two gaze—throw calibrations (prism and no-prism) were retained for >27 months. The long-term adjustment was shown to consist of a coordinated relationship of eye-in-head, head-on-trunk and trunk-on-arm angles.
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paper_title: Prism Adaptation and Aftereffect: Specifying the Properties of a Procedural Memory System

paper_content:

Prism adaptation, a form of procedural learning, is a phenomenon in which the motor system adapts to new visuospatial coordinates imposed by prisms that displace the visual field. Once the prisms are withdrawn, the degree and strength of the adaptation can be measured by the spatial deviation of the motor actions in the direction opposite to the visual displacement imposed by the prisms, a phenomenon known as aftereffect. This study was designed to define the variables that affect the acquisition and retention of the aftereffect. Subjects were required to throw balls to a target in front of them before, during, and after lateral displacement of the visual field with prismatic spectacles. The diopters of the prisms and the number of throws were varied among different groups of subjects. The results show that the adaptation process is dependent on the number of interactions between the visual and motor system, and not on the time spent wearing the prisms. The results also show that the magnitude of the aftereffect is highly correlated with the magnitude of the adaptation, regardless of the diopters of the prisms or the number of throws. Finally, the results suggest that persistence of the aftereffect depends on the number of throws after the adaptation is complete. On the basis of these results, we propose that the system underlying this kind of learning stores at least two different parameters, the contents (measured as the magnitude of displacement) and the persistence (measured as the number of throws to return to the baseline) of the learned information.
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paper_title: Nonvisually Guided Locomotion to a Previously Viewed Target in Real and Virtual Environments

paper_content:

Comparing human performance in a virtual environment (VE) with performance in the real world can provide clues about which aspects of VE technology require improvement. Using a technique previously shown to measure real-world distance judgments accurately, we compared performance in a real-world environment with performance in a virtual model of that environment. The technique required participants to walk without vision to a target after viewing it for 10 s. VE distance judgments averaged 85% of the target distance, whereas real-world judgments averaged 92%. The magnitude of the relative errors in the VE was twice that in the real world, indicating that the VE degraded distance judgments. Our analysis suggests that VE performance deficits result either from poor binocular disparity cues or from distortion of pictorial depth cues. Actual or potential applications of this research include the development of virtual environments for training and the design of visual displays for virtual simulations.
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paper_title: Correcting distance estimates by interacting with immersive virtual environments: Effects of task and available sensory information

paper_content:

The tendency to underestimate egocentric distances in immersive virtual environments (VEs) is not well understood. However, previous research (A. R. Richardson and D. Waller, 2007) has demonstrated that a brief period of interaction with the VE prior to making distance judgments can effectively eliminate subsequent underestimation. Here the authors examine the mechanism underlying the effect of VE interaction and the conditions that may give rise to it. In Experiment 1, after interacting with an immersive VE, participants tended to overestimate distances in the physical world, indicating that the interaction involved a recalibration of the perceptual-motor system. Experiment 2 demonstrates that visual information is not necessary (and that body-based information is necessary) during the interaction period for it to have a positive effect on subsequent distance estimation accuracy. Experiment 3 illustrates that the interaction task does not need to be goal directed in order to be effective. Language: en
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paper_title: Correlations Between Physiological Response, Gait, Personality, and Presence in Immersive Virtual Environments

paper_content:

In previous work, we have found significant differences in the accuracy with which people make initial spatial judgments in different types of head-mounted, display-based immersive virtual environments (IVEs; Phillips, Interrante, Kaeding, Ries, & Anderson, 2010). In particular, we have found that people tend to less severely underestimate egocentric distances in a virtual environment that is a photorealistic replica of a real place that they have recently visited than when the virtual environment is either a photorealistic replica of an unfamiliar place, or a nonphotorealistically (NPR) portrayed version of a familiar space. We have also noted significant differences in the effect of environment type on distance perception accuracy between individual participants. In this paper, we report the results of two experiments that seek further insight into these phenomena, focusing on factors related to depth of presence in the virtual environment. In our reported first experiment, we immersed users (between-subjects) in one of the three different types of IVEs and asked them to perform a series of well-defined tasks along a delimited path, first in a control version of the environment, and then in a stressful variant in which the floor around the marked path was cut away to reveal a 20-ft drop. We assessed participants' sense of presence during each trial using a diverse set of measures, including: questionnaires, recordings of heart rate and galvanic skin response, and gait metrics derived from tracking data. We computed the differences in each of these measures between the stressful and nonstressful versions of each environment, and then compared the changes due to stress between the different virtual environment conditions. Pooling the data over all participants in each group, we found significant physiological indications of stress after the appearance of the pit in all three environments, but we did not find significant differences in the magnitude of the stress response between the different virtual environment locales. We also did not find any significant difference in the level of subjective presence reported in each environment. However, we did find significant differences in gait: participants in the photorealistic replica room showed a significantly greater reduction in stride speed and stride length between the control and pit version of the room than did participants in either the photorealistically rendered nonreplica environment or the NPR replica environment conditions. Our second experiment, conducted with a new set of participants, sought to more directly investigate potential correlations between distance estimation accuracy and personality, stress response, and reported sense of presence, comparatively across different immersive virtual environment conditions. We used pretest questionnaires to assess a variety of personality measures, and then randomly immersed participants (between-subjects) in either the photorealistic replica or photorealistic non-replica environment and assessed the accuracy of their egocentric distance judgments in that IVE, followed by control trials in a neutral, real-world location. We then had participants go through the same set of tasks as in our first experiment while we collected physiological measures of their stress level and tracked their gait, and we compared the changes in these measures between the neutral and pit-enhanced versions of the environment. Finally, we had people fill out a brief presence questionnaire.Analyzing all of these data, we found that participants made significantly greater distance estimation errors in the unfamiliar room environment than in the replica room environment, but no other differences between the two environments were significant. We found significant positive correlation between several of the personality measures, but we did not find any notable significant correlations between personality and presence, or between either personality or presence and gait changes or distance estimation accuracy. These results suggest to us that the relationship between personality, presence, and performance in IVEs is complicated and not easily captured by existing measures.
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paper_title: Distance perception in NPR immersive virtual environments, revisited

paper_content:

Non-photorealistic rendering (NPR) is a representational technique that allows communicating the essence of a design while giving the viewer the sense that the design is open to change. Our research aims to address the question of how to effectively use non-photorealistic rendering in immersive virtual environments to enable the intuitive exploration of early architectural design concepts at full scale. Previous studies have shown that people typically underestimate egocentric distances in immersive virtual environments, regardless of rendering style, although we have recently found that distance estimation errors are minimized in the special case that the virtual environment is a high-fidelity replica of a real environment that the viewer is presently in or has recently been in. In this paper we re-examine the impact of rendering style on distance perception accuracy in this virtual environments context. Specifically, we report the results of an experiment that seeks to assess the accuracy with which people judge distances in a non-photorealistically rendered virtual environment that is a directly-derived stylistic abstraction of the actual environment that they are currently in. Our results indicate that people tend to underestimate distances to a significantly greater extent in a co-located virtual environment when it is rendered using a line-drawing style than when it is rendered using high fidelity textures derived from photographs.
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paper_title: The influence of feedback on egocentric distance judgments in real and virtual environments

paper_content:

A number of investigators have reported that distance judgments in virtual environments (VEs) are systematically smaller than distance judgments made in comparably-sized real environments. Many variables that may contribute to this difference have been investigated but none of them fully explain the distance compression. One approach to this problem that has implications for both VE applications and the study of perceptual mechanisms is to examine the influence of the feedback available to the user. Most generally, we asked whether feedback within a virtual environment would lead to more accurate estimations of distance. Next, given the prediction that some change in behavior would be observed, we asked whether specific adaptation effects would generalize to other indications of distance. Finally, we asked whether these effects would transfer from the VE to the real world. All distance judgments in the head-mounted display (HMD) became near accurate after three different forms of feedback were given within the HMD. However, not all feedback sessions within the HMD altered real world distance judgments. These results are discussed with respect to the perceptual and cognitive mechanisms that may be involved in the observed adaptation effects as well as the benefits of feedback for VE applications.
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paper_title: The influence of eye height and avatars on egocentric distance estimates in immersive virtual environments

paper_content:

It is well known that eye height is an important visual cue in the perception of apparent sizes and affordances in virtual environments. However, the influence of visual eye height on egocentric distances in virtual environments has received less attention. To explore this influence, we conducted an experiment where we manipulated the virtual eye height of the user in a head-mounted display virtual environment. As a measurement we asked the participants to verbally judge egocentric distances and to give verbal estimates of the dimensions of the virtual room. In addition, we provided the participants a self-animated avatar to investigate if this virtual self-representation has an impact on the accuracy of verbal distance judgments, as recently evidenced for distance judgments accessed with an action-based measure. When controlled for ownership, the avatar had a significant influence on the verbal estimates of egocentric distances as found in previous research. Interestingly, we found that the manipulation of eye height has a significant influence on the verbal estimates of both egocentric distances and the dimensions of the room. We discuss the implications which these research results have on those interested in space perception in both immersive virtual environments and the real world.
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paper_title: Technical Section: A review of virtual environments for training in ball sports

paper_content:

There is growing interest in utilising virtual environments (VEs) in the context of sports. In particular there is a desire to be able to improve sensorimotor skills rather than just using a VE as a tool for strategy analysis, or entertainment. The range of skills required across all different sports is very large and varied. This review of the state-of-the-art, therefore focuses on just ball sports, and was carried out as part of a current project developing training tools for rugby. A VE needs to provide realistic rendering of the sports scene to achieve good perceptual fidelity. More important for a sport-themed VE is high functional fidelity, which requires an accurate physics model of a complex environment, real time response, and a natural user interface. The goal is to provide multiple scenarios to players at different levels of difficulty, providing them with improved skills that can be applied directly to the real sports arena. The typical hardware and software components needed are identified in the paper, and important psychological factors that should be considered are discussed. The challenges that need to be overcome are identified and illustrated with examples from recent projects in this area.
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paper_title: Estimating Distance in Real and Virtual Environments: Does Order Make a Difference?

paper_content:

In this investigation, we examined how the order in which people experience real and virtual environments influences their distance estimates. Participants made two sets of distance estimates in one of the following conditions: (1) real environment first, virtual environment second; (2) virtual environment first, real environment second; (3) real environment first, real environment second; or (4) virtual environment first, virtual environment second. In Experiment 1, the participants imagined how long it would take to walk to targets in real and virtual environments. The participants’ first estimates were significantly more accurate in the real than in the virtual environment. When the second environment was the same as the first environment (real-real and virtual-virtual), the participants’ second estimates were also more accurate in the real than in the virtual environment. When the second environment differed from the first environment (real-virtual and virtual-real), however, the participants’ second estimates did not differ significantly across the two environments. A second experiment, in which the participants walked blindfolded to targets in the real environment and imagined how long it would take to walk to targets in the virtual environment, replicated these results. These subtle yet persistent order effects suggest that memory can play an important role in distance perception.
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paper_title: A full-body avatar improves egocentric distance judgments in an immersive virtual environment

paper_content:

A number of investigators have reported that distance judgments in virtual environments (VEs) are systematically smaller than distance judgments made in comparably-sized real environments. Many variables that may contribute to this difference have been investigated but none of them fully explain the distance compression. In this paper we asked whether seeing a fully-articulated visual representation of oneself (avatar) within a virtual environment would lead to more accurate estimations of distance. We found that participants who explored near space without the visual avatar underestimated egocentric distance judgments compared to those who similarly explored near space while viewing a fully-articulated avatar. These results are discussed with respect to the perceptual and cognitive mechanisms that may be involved in the observed effects as well as the benefits of visual feedback in the form of an avatar for VE applications.
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paper_title: Enhancing Presence in Head-Mounted Display Environments by Visual Body Feedback Using Head-Mounted Cameras

paper_content:

A fully-articulated visual representation of a user in an immersive virtual environment (IVE) can enhance the user's subjective sense of feeling present in the virtual world. Usually this requires the user to wear a full-body motion capture suit to track real-world body movements and to map them to a virtual body model. In this paper we present an augmented virtuality approach that allows to incorporate a realistic view of oneself in virtual environments using cameras attached to head mounted displays. The described system can easily be integrated into typical virtual reality setups. Egocentric camera images captured by a video-see-through system are segmented in real-time into foreground, showing parts of the user's body, e. g., her hands or feet, and background. The segmented foreground is then displayed as inset in the user's current view of the virtual world. Thus the user is able to see her physical body in an arbitrary virtual world, including individual characteristics such as skin pigmentation and hairiness.
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paper_title: Avatar self-embodiment enhances distance perception accuracy in non-photorealistic immersive virtual environments

paper_content:

Non-photorealistically rendered (NPR) immersive virtual environments (IVEs) can facilitate conceptual design in architecture by enabling preliminary design sketches to be previewed and experienced at full scale, from a first-person perspective. However, it is critical to ensure the accurate spatial perception of the represented information, and many studies have shown that people typically underestimate distances in most IVEs, regardless of rendering style. In previous work we have found that while people tend to judge distances more accurately in an IVE that is a high-fidelity replica of their concurrently occupied real environment than in an IVE that it is a photorealistic representation of a real place that they've never been to, significant distance estimation errors re-emerge when the replica environment is represented in a NPR style. We have also previously found that distance estimation accuracy can be improved, in photo-realistically rendered novel virtual environments, when people are given a fully tracked, high fidelity first person avatar self-embodiment. In this paper we report the results of an experiment that seeks to determine whether providing users with a high-fidelity avatar self-embodiment in a NPR virtual replica environment will enable them to perceive the 3D spatial layout of that environment more accurately. We find that users who are given a first person avatar in an NPR replica environment judge distances more accurately than do users who experience the NPR replica room without an embodiment, but not as accurately as users whose distance judgments are made in a photorealistically rendered virtual replica room. Our results provide a partial solution to the problem of facilitating accurate distance perception in NPR virtual environments, while supporting and expanding the scope of previous findings that giving people a realistic avatar self-embodiment in an IVE can help them to interpret what they see through an HMD in a way that is more similar to how they would interpret a corresponding visual stimulus in the real world.
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paper_title: Elucidating Factors that Can Facilitate Veridical Spatial Perception in Immersive Virtual Environments

paper_content:

Ensuring veridical spatial perception in immersive virtual environments (IVEs) is an important yet elusive goal. In this paper, we present the results of two experiments that seek further insight into this problem. In the first of these experiments, initially reported in Interrante, Ries, Lindquist, and Anderson (2007), we seek to disambiguate two alternative hypotheses that could explain our recent finding (Interrante, Anderson, and Ries, 2006a) that participants appear not to significantly underestimate egocentric distances in HMD-based IVEs, relative to in the real world, in the special case that they unambiguously know, through first-hand observation, that the presented virtual environment is a high-fidelity 3D model of their concurrently occupied real environment. Specifically, we seek to determine whether people are able to make similarly veridical judgments of egocentric distances in these matched real and virtual environments because (1) they are able to use metric information gleaned from their exposure to the real environment to calibrate their judgments of sizes and distances in the matched virtual environment, or because (2) their prior exposure to the real environment enabled them to achieve a heightened sense of presence in the matched virtual environment, which leads them to act on the visual stimulus provided through the HMD as if they were interpreting it as a computer-mediated view of an actual real environment, rather than just as a computer-generated picture, with all of the uncertainties that that would imply. In our second experiment, we seek to investigate the extent to which augmenting a virtual environment model with faithfully-modeled replicas of familiar objects might enhance people's ability to make accurate judgments of egocentric distances in that environment.
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paper_title: Prism Adaptation and Aftereffect: Specifying the Properties of a Procedural Memory System

paper_content:

Prism adaptation, a form of procedural learning, is a phenomenon in which the motor system adapts to new visuospatial coordinates imposed by prisms that displace the visual field. Once the prisms are withdrawn, the degree and strength of the adaptation can be measured by the spatial deviation of the motor actions in the direction opposite to the visual displacement imposed by the prisms, a phenomenon known as aftereffect. This study was designed to define the variables that affect the acquisition and retention of the aftereffect. Subjects were required to throw balls to a target in front of them before, during, and after lateral displacement of the visual field with prismatic spectacles. The diopters of the prisms and the number of throws were varied among different groups of subjects. The results show that the adaptation process is dependent on the number of interactions between the visual and motor system, and not on the time spent wearing the prisms. The results also show that the magnitude of the aftereffect is highly correlated with the magnitude of the adaptation, regardless of the diopters of the prisms or the number of throws. Finally, the results suggest that persistence of the aftereffect depends on the number of throws after the adaptation is complete. On the basis of these results, we propose that the system underlying this kind of learning stores at least two different parameters, the contents (measured as the magnitude of displacement) and the persistence (measured as the number of throws to return to the baseline) of the learned information.
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paper_title: Calibration of human locomotion and models of perceptual-motor organization.

paper_content:

People coordinate the force and direction of skilled actions with target locations and adjust the calibrations to compensate for changing circumstances. Are the adjustments globally organized (adjusting a particular action to fit a particular circumstance would generalize to all actions in the same circumstance); anatomically specific (every effector is adjusted independently of others); of functional (adjustments would generalize to all actions serving the same goal and generating the same perceptible consequences)? Across 10 experiments, changes in the calibration of walking, throwing, and turning-in-place were induced, and generalization of changes in calibration to functionally related and unrelated actions were tested. The experiments demonstrate that humans rapidly adjust the calibration of their walking, turning, and throwing to changing circumstances, and a functional model of perceptual-motor organization is suggested.
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paper_title: Analyzing the effect of a virtual avatar's geometric and motion fidelity on ego-centric spatial perception in immersive virtual environments

paper_content:

Previous work has shown that giving a user a first-person virtual avatar can increase the accuracy of their egocentric distance judgments in an immersive virtual environment (IVE). This result provides one of the rare examples of a manipulation that can enable improved spatial task performance in a virtual environment without potentially compromising the ability for accurate information transfer to the real world. However, many open questions about the scope and limitations of the effectiveness of IVE avatar self-embodiment remain. In this paper, we report the results of a series of four experiments, involving a total of 40 participants, that explore the importance, to the desired outcome of enabling enhanced spatial perception accuracy, of providing a high level of geometric and motion fidelity in the avatar representation. In these studies, we assess participants' abilities to estimate egocentric distances in a novel virtual environment under four different conditions of avatar self-embodiment: a) no avatar; b) a fully tracked, custom-fitted, high fidelity avatar, represented using a textured triangle mesh; c) the same avatar as in b) but implemented with single point rather than full body tracking; and d) a fully tracked but simplified avatar, represented by a collection of small spheres at the raw tracking marker locations. The goal of these investigations is to attain insight into what specific characteristics of a virtual avatar representation are most important to facilitating accurate spatial perception, and what cost-saving measures in the avatar implementation might be possible. Our results indicate that each of the simplified avatar implementations we tested is significantly less effective than the full avatar in facilitating accurate distance estimation; in fact, the participants who were given the simplified avatar representations performed only marginally (but not significantly) more accurately than the participants who were given no avatar at all. These findings suggest that the beneficial impact of providing users with a high fidelity avatar self-representation may stem less directly from the low-level size and motion cues that the avatar embodiment makes available to them than from the cognitive sense of presence that the self-embodiment supports.
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paper_title: Distance perception in real and virtual environments

paper_content:

Two experiments were conducted to compare distance perception in real and virtual environments. In Experiment 1, adults estimated how long it would take to walk to targets in real and virtual environments by starting and stopping a stopwatch while looking at a target person standing between 20 and 120 ft away. The real environment was a large grassy lawn in front of a university building. We replicated this scene in our virtual environment using a nonstereoscopic, large screen immersive display system. We found that people underestimated time to walk in both environments for distances of 40--60 ft and beyond. However, time-to-walk estimates were virtually identical across the two environments. In Experiment 2, 10- and 12-year-old children and adults estimated time to walk in real and virtual environments both with and without vision. Adults again underestimated time to walk in both environments for distances of 60 ft and beyond. Again, their estimates were virtually identical in the real and virtual environment both with and without vision. Children's time-to-walk estimates were also very similar across the two environments under both viewing conditions. We conclude that distance perception may be better in virtual environments involving large screen immersive displays than those involving head mounted displays (HMDs).
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paper_title: Nonvisually Guided Locomotion to a Previously Viewed Target in Real and Virtual Environments

paper_content:

Comparing human performance in a virtual environment (VE) with performance in the real world can provide clues about which aspects of VE technology require improvement. Using a technique previously shown to measure real-world distance judgments accurately, we compared performance in a real-world environment with performance in a virtual model of that environment. The technique required participants to walk without vision to a target after viewing it for 10 s. VE distance judgments averaged 85% of the target distance, whereas real-world judgments averaged 92%. The magnitude of the relative errors in the VE was twice that in the real world, indicating that the VE degraded distance judgments. Our analysis suggests that VE performance deficits result either from poor binocular disparity cues or from distortion of pictorial depth cues. Actual or potential applications of this research include the development of virtual environments for training and the design of visual displays for virtual simulations.
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paper_title: Correcting distance estimates by interacting with immersive virtual environments: Effects of task and available sensory information

paper_content:

The tendency to underestimate egocentric distances in immersive virtual environments (VEs) is not well understood. However, previous research (A. R. Richardson and D. Waller, 2007) has demonstrated that a brief period of interaction with the VE prior to making distance judgments can effectively eliminate subsequent underestimation. Here the authors examine the mechanism underlying the effect of VE interaction and the conditions that may give rise to it. In Experiment 1, after interacting with an immersive VE, participants tended to overestimate distances in the physical world, indicating that the interaction involved a recalibration of the perceptual-motor system. Experiment 2 demonstrates that visual information is not necessary (and that body-based information is necessary) during the interaction period for it to have a positive effect on subsequent distance estimation accuracy. Experiment 3 illustrates that the interaction task does not need to be goal directed in order to be effective. Language: en
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paper_title: Correlations Between Physiological Response, Gait, Personality, and Presence in Immersive Virtual Environments

paper_content:

In previous work, we have found significant differences in the accuracy with which people make initial spatial judgments in different types of head-mounted, display-based immersive virtual environments (IVEs; Phillips, Interrante, Kaeding, Ries, & Anderson, 2010). In particular, we have found that people tend to less severely underestimate egocentric distances in a virtual environment that is a photorealistic replica of a real place that they have recently visited than when the virtual environment is either a photorealistic replica of an unfamiliar place, or a nonphotorealistically (NPR) portrayed version of a familiar space. We have also noted significant differences in the effect of environment type on distance perception accuracy between individual participants. In this paper, we report the results of two experiments that seek further insight into these phenomena, focusing on factors related to depth of presence in the virtual environment. In our reported first experiment, we immersed users (between-subjects) in one of the three different types of IVEs and asked them to perform a series of well-defined tasks along a delimited path, first in a control version of the environment, and then in a stressful variant in which the floor around the marked path was cut away to reveal a 20-ft drop. We assessed participants' sense of presence during each trial using a diverse set of measures, including: questionnaires, recordings of heart rate and galvanic skin response, and gait metrics derived from tracking data. We computed the differences in each of these measures between the stressful and nonstressful versions of each environment, and then compared the changes due to stress between the different virtual environment conditions. Pooling the data over all participants in each group, we found significant physiological indications of stress after the appearance of the pit in all three environments, but we did not find significant differences in the magnitude of the stress response between the different virtual environment locales. We also did not find any significant difference in the level of subjective presence reported in each environment. However, we did find significant differences in gait: participants in the photorealistic replica room showed a significantly greater reduction in stride speed and stride length between the control and pit version of the room than did participants in either the photorealistically rendered nonreplica environment or the NPR replica environment conditions. Our second experiment, conducted with a new set of participants, sought to more directly investigate potential correlations between distance estimation accuracy and personality, stress response, and reported sense of presence, comparatively across different immersive virtual environment conditions. We used pretest questionnaires to assess a variety of personality measures, and then randomly immersed participants (between-subjects) in either the photorealistic replica or photorealistic non-replica environment and assessed the accuracy of their egocentric distance judgments in that IVE, followed by control trials in a neutral, real-world location. We then had participants go through the same set of tasks as in our first experiment while we collected physiological measures of their stress level and tracked their gait, and we compared the changes in these measures between the neutral and pit-enhanced versions of the environment. Finally, we had people fill out a brief presence questionnaire.Analyzing all of these data, we found that participants made significantly greater distance estimation errors in the unfamiliar room environment than in the replica room environment, but no other differences between the two environments were significant. We found significant positive correlation between several of the personality measures, but we did not find any notable significant correlations between personality and presence, or between either personality or presence and gait changes or distance estimation accuracy. These results suggest to us that the relationship between personality, presence, and performance in IVEs is complicated and not easily captured by existing measures.
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paper_title: Distance perception in NPR immersive virtual environments, revisited

paper_content:

Non-photorealistic rendering (NPR) is a representational technique that allows communicating the essence of a design while giving the viewer the sense that the design is open to change. Our research aims to address the question of how to effectively use non-photorealistic rendering in immersive virtual environments to enable the intuitive exploration of early architectural design concepts at full scale. Previous studies have shown that people typically underestimate egocentric distances in immersive virtual environments, regardless of rendering style, although we have recently found that distance estimation errors are minimized in the special case that the virtual environment is a high-fidelity replica of a real environment that the viewer is presently in or has recently been in. In this paper we re-examine the impact of rendering style on distance perception accuracy in this virtual environments context. Specifically, we report the results of an experiment that seeks to assess the accuracy with which people judge distances in a non-photorealistically rendered virtual environment that is a directly-derived stylistic abstraction of the actual environment that they are currently in. Our results indicate that people tend to underestimate distances to a significantly greater extent in a co-located virtual environment when it is rendered using a line-drawing style than when it is rendered using high fidelity textures derived from photographs.
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paper_title: Accommodation, occlusion, and disparity matching are used to guide reaching: a comparison of actual versus virtual environments.

paper_content:

The authors used a virtual environment to investigate visual control of reaching and monocular and binocular perception of egocentric distance, size, and shape. With binocular vision, the results suggested use of disparity matching. This was tested and confirmed in the virtual environment by eliminating other information about contact of hand and target. Elimination of occlusion of hand by target destabilized monocular but not binocular performance. Because the virtual environment entails accommodation of an image beyond reach, the authors predicted overestimation of egocentric distances in the virtual relative to actual environment. This was confirmed. The authors used -2 diopter glasses to reduce the focal distance in the virtual environment. Overestimates were reduced by half. The authors conclude that calibration of perception is required for accurate feedforward reaching and that disparity matching is optimal visual information for calibration.
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paper_title: Perception and action

paper_content:

The phrase perception and action is used widely but in diverse ways in the context of the relationship between perceptual and motor processes. This review describes and integrates five perspectives on perception and action which rely on both neurophysiological and behavioral levels of analysis. The two visual systems view proposes dissociable but interactive systems for conscious processing of objects/space and the visual control of action. The integrative view proposes tightly calibrated but flexible systems for perception and motor control in spatial representation. The embodied view posits that action underlies perception, involving common coding or motor simulation systems, and examines the relationship between action observation, imitation, and the understanding of intention. The ecological view emphasizes environmental information and affordances in perception. The functional view defines the relationship between perception, action planning, and semantics in goal-directed actions. Although some of these views/approaches differ in significant ways, their shared emphasis on the importance of action in perception serves as a useful unifying framework. WIREs Cogn Sci 2010 1 800–810 ::: ::: ::: ::: For further resources related to this article, please visit the WIREs website
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paper_title: The influence of restricted viewing conditions on egocentric distance perception: Implications for real and virtual environments

paper_content:

We carried out three experiments to examine the influence of field of view and binocular viewing restrictions on absolute distance perception in real-world indoor environments. Few of the classical visual cues provide direct information for accurate absolute distance judgments to points in the environment beyond about 2 m from the viewer. Nevertheless, in previous work it has been found that visually directed walking tasks reveal accurate distance estimations in full-cue real-world environments to distances up to 20 m. In contrast, the same tasks in virtual environments produced with head-mounted displays (HMDs) show large compression of distance. Field of view and binocular viewing are common limitations in research with HMDs, and have been rarely studied under full pictorial-cue conditions in the context of distance perception in the real-world. Experiment 1 showed that the view of one's body and feet on the floor was not necessary for accurate distance perception. In experiment 2 we manipulated the hor...
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paper_title: Estimation of distances in virtual environments using size constancy

paper_content:

It is reported in the literature that distances from ::: the observer are underestimated more in virtual environments ::: (VEs) than in physical world conditions. On the other hand ::: estimation of size in VEs is quite accurate and follows a ::: size-constancy law when rich cues are present. This study ::: investigates how estimation of distance in a CAVETM ::: environment is affected by poor and rich cue conditions, subject ::: experience, and environmental learning when the position of the ::: objects is estimated using an experimental paradigm that ::: exploits size constancy. ::: A group of 18 healthy participants was asked to move a ::: virtual sphere controlled using the wand joystick to the position ::: where they thought a previously-displayed virtual cube ::: (stimulus) had appeared. Real-size physical models of the virtual ::: objects were also presented to the participants as a reference of ::: real physical distance during the trials. An accurate estimation ::: of distance implied that the participants assessed the relative size ::: of sphere and cube correctly. The cube appeared at depths ::: between 0.6 m and 3 m, measured along the depth direction of ::: the CAVE. The task was carried out in two environments: a ::: poor cue one with limited background cues, and a rich cue one ::: with textured background surfaces. ::: It was found that distances were underestimated in both poor ::: and rich cue conditions, with greater underestimation in the ::: poor cue environment. The analysis also indicated that factors ::: such as subject experience and environmental learning were not ::: influential. However, least square fitting of Stevens’ power law ::: indicated a high degree of accuracy during the estimation of ::: object locations. This accuracy was higher than in other studies ::: which were not based on a size-estimation paradigm. Thus as ::: indirect result, this study appears to show that accuracy when ::: estimating egocentric distances may be increased using an ::: experimental method that provides information on the relative ::: size of the objects used.
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paper_title: Estimating Distance in Real and Virtual Environments: Does Order Make a Difference?

paper_content:

In this investigation, we examined how the order in which people experience real and virtual environments influences their distance estimates. Participants made two sets of distance estimates in one of the following conditions: (1) real environment first, virtual environment second; (2) virtual environment first, real environment second; (3) real environment first, real environment second; or (4) virtual environment first, virtual environment second. In Experiment 1, the participants imagined how long it would take to walk to targets in real and virtual environments. The participants’ first estimates were significantly more accurate in the real than in the virtual environment. When the second environment was the same as the first environment (real-real and virtual-virtual), the participants’ second estimates were also more accurate in the real than in the virtual environment. When the second environment differed from the first environment (real-virtual and virtual-real), however, the participants’ second estimates did not differ significantly across the two environments. A second experiment, in which the participants walked blindfolded to targets in the real environment and imagined how long it would take to walk to targets in the virtual environment, replicated these results. These subtle yet persistent order effects suggest that memory can play an important role in distance perception.
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paper_title: Avatar self-embodiment enhances distance perception accuracy in non-photorealistic immersive virtual environments

paper_content:

Non-photorealistically rendered (NPR) immersive virtual environments (IVEs) can facilitate conceptual design in architecture by enabling preliminary design sketches to be previewed and experienced at full scale, from a first-person perspective. However, it is critical to ensure the accurate spatial perception of the represented information, and many studies have shown that people typically underestimate distances in most IVEs, regardless of rendering style. In previous work we have found that while people tend to judge distances more accurately in an IVE that is a high-fidelity replica of their concurrently occupied real environment than in an IVE that it is a photorealistic representation of a real place that they've never been to, significant distance estimation errors re-emerge when the replica environment is represented in a NPR style. We have also previously found that distance estimation accuracy can be improved, in photo-realistically rendered novel virtual environments, when people are given a fully tracked, high fidelity first person avatar self-embodiment. In this paper we report the results of an experiment that seeks to determine whether providing users with a high-fidelity avatar self-embodiment in a NPR virtual replica environment will enable them to perceive the 3D spatial layout of that environment more accurately. We find that users who are given a first person avatar in an NPR replica environment judge distances more accurately than do users who experience the NPR replica room without an embodiment, but not as accurately as users whose distance judgments are made in a photorealistically rendered virtual replica room. Our results provide a partial solution to the problem of facilitating accurate distance perception in NPR virtual environments, while supporting and expanding the scope of previous findings that giving people a realistic avatar self-embodiment in an IVE can help them to interpret what they see through an HMD in a way that is more similar to how they would interpret a corresponding visual stimulus in the real world.
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paper_title: Depth Perception in Virtual Reality: Distance Estimations in Peri- and Extrapersonal Space

paper_content:

ABSTRACT The present study investigated depth perception in virtual environments. Twenty-three participants verbally estimated ten distances between 40 cm and 500 cm in three different virtual environments in two conditions: (1) only one target was presented or (2) ten targets were presented at the same time. Additionally, the presence of a metric aid was varied. A questionnaire assessed subjective ratings about physical complaints (e.g., headache), the experience in the virtual world (e.g., presence), and the experiment itself (self-evaluation of the estimations). Results show that participants underestimate the virtual distances but are able to perceive the distances in the right metric order even when only very simple virtual environments are presented. Furthermore, interindividual differences and intraindividual stabilities can be found among participants, and neither the three different virtual environments nor the metric aid improved depth estimations. Estimation performance is better in peripersona...
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paper_title: On the Determinants of Size-Constancy in a Virtual Environment

paper_content:

—An important aspect of a subject’s perception of ::: virtual objects in a virtual environment is whether the size of the ::: object is perceived as it would be in the physical world, which is ::: named size-constancy. The ability of subjects to appreciate ::: size-constancy in an immersive virtual environment was studied ::: while scene complexity, stereovision and motion parallax visual ::: factors were manipulated resulting in twelve different viewing ::: conditions. Under each visual condition, 18 subjects made size ::: judgments of a virtual object displayed at five different distances ::: from them. Responses from the majority of our population ::: demonstrated that scene complexity and stereovision have a ::: significant impact on subjects’ ability to appreciate size-constancy. ::: In contrast, motion parallax produced by moving the virtual ::: environment or by the movements of the observer alone proved ::: not to be a significant factor in determining size-constancy ::: performance. Consequently, size-constancy is best obtained when ::: scene complexity and stereovision are components of the viewing ::: conditions.
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paper_title: Aging and the perception of egocentric distance.

paper_content:

The present study examined whether there is an age-related difference in judging egocentric distances. In 4 experiments, both younger and older observers judged the physical distance of an object on a ground plane and reported their judgments by verbal report and by blind rope pulling. Overall, we found that (a) younger observers in general underestimated egocentric distance and showed foreshortening; (b) older observers judged more egocentric distance than younger observers and did not show foreshortening; and (c) this age-related difference was not due to an age-related difference in scaling or output calibration (Experiment 2), the use of eye height information (Experiment 3), or the use of texture gradient information (Experiment 4). These results may be accounted for by differences in perceived slant of the ground surface or a greater reliance on pictorial cues with increased age.
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paper_title: Size-Constancy in the CAVE

paper_content:

The use of virtual environments (VE) for many research and commercial purposes relies on its ability to generate environments that faithfully reproduce the physical world. However, due to its limitations the VE can have a number of flaws that adversely affect its use and believability. One of the more important aspects of this problem is whether the size of an object in the VE is perceived as it would be in the physical world. One of the fundamental phenomena for correct size is size-constancy, that is, an object is perceived to be the same size regardless of its distance from the observer. This is in spite of the fact that the retinal size of the object shrinks with increasing distance from the observer. We examined size-constancy in the CAVE and found that size-constancy is a strong and dominant perception in our subject population when the test object is accompanied by surrounding environmental objects. Furthermore, size-constancy changes to a visual angle performance (i.e., object size changed with distance from the subject) when these surrounding objects are removed from the scene. As previously described for the physical world, our results suggest that it is necessary to provide surrounding objects to aid in the determination of an object's depth and to elicit size-constancy in VE. These results are discussed regarding their implications for viewing objects in projection-based VE and the environments that play a role in the perception of object size in the CAVE.
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paper_title: Analyzing the effect of a virtual avatar's geometric and motion fidelity on ego-centric spatial perception in immersive virtual environments

paper_content:

Previous work has shown that giving a user a first-person virtual avatar can increase the accuracy of their egocentric distance judgments in an immersive virtual environment (IVE). This result provides one of the rare examples of a manipulation that can enable improved spatial task performance in a virtual environment without potentially compromising the ability for accurate information transfer to the real world. However, many open questions about the scope and limitations of the effectiveness of IVE avatar self-embodiment remain. In this paper, we report the results of a series of four experiments, involving a total of 40 participants, that explore the importance, to the desired outcome of enabling enhanced spatial perception accuracy, of providing a high level of geometric and motion fidelity in the avatar representation. In these studies, we assess participants' abilities to estimate egocentric distances in a novel virtual environment under four different conditions of avatar self-embodiment: a) no avatar; b) a fully tracked, custom-fitted, high fidelity avatar, represented using a textured triangle mesh; c) the same avatar as in b) but implemented with single point rather than full body tracking; and d) a fully tracked but simplified avatar, represented by a collection of small spheres at the raw tracking marker locations. The goal of these investigations is to attain insight into what specific characteristics of a virtual avatar representation are most important to facilitating accurate spatial perception, and what cost-saving measures in the avatar implementation might be possible. Our results indicate that each of the simplified avatar implementations we tested is significantly less effective than the full avatar in facilitating accurate distance estimation; in fact, the participants who were given the simplified avatar representations performed only marginally (but not significantly) more accurately than the participants who were given no avatar at all. These findings suggest that the beneficial impact of providing users with a high fidelity avatar self-representation may stem less directly from the low-level size and motion cues that the avatar embodiment makes available to them than from the cognitive sense of presence that the self-embodiment supports.
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paper_title: The effect of isolated disparity on depth perception in real and virtual environments

paper_content:

In this paper, we investigated depth perception in real and virtual environments when binocular disparity is the sole distance cue. The observers were asked to estimate the relative depth of spheres verbally in virtual and actual environments. Constant apparent sized stimuli were used to measure the just-noticeable difference in depth perception, thus avoiding providing a size gradient cue. Results of the experiments revealed individual differences in virtual reality in contrast to reality. Specifically a subgroup of observers had difficulty perceiving the depth of virtual spheres in virtual reality, which may indicate that they rely on apparent size for judging depth. Furthermore, the just-noticeable differences were more variable in the virtual environment than with real objects. Our results reveal individual differences when the disparity-driven convergence cue is the only distance cue provided in virtual reality.
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paper_title: Distance perception in real and virtual environments

paper_content:

Two experiments were conducted to compare distance perception in real and virtual environments. In Experiment 1, adults estimated how long it would take to walk to targets in real and virtual environments by starting and stopping a stopwatch while looking at a target person standing between 20 and 120 ft away. The real environment was a large grassy lawn in front of a university building. We replicated this scene in our virtual environment using a nonstereoscopic, large screen immersive display system. We found that people underestimated time to walk in both environments for distances of 40--60 ft and beyond. However, time-to-walk estimates were virtually identical across the two environments. In Experiment 2, 10- and 12-year-old children and adults estimated time to walk in real and virtual environments both with and without vision. Adults again underestimated time to walk in both environments for distances of 60 ft and beyond. Again, their estimates were virtually identical in the real and virtual environment both with and without vision. Children's time-to-walk estimates were also very similar across the two environments under both viewing conditions. We conclude that distance perception may be better in virtual environments involving large screen immersive displays than those involving head mounted displays (HMDs).
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Title: The Perception of Egocentric Distances in Virtual Environments - A Review
Section 1: INTRODUCTION
Description 1: Write an introductory section detailing the significance, applications, and necessity of veridical distance perception in virtual environments, and outline the aim of the review to survey the current state of research.

Section 2: Distance Perception in Real Environments
Description 2: Summarize research on visual distance perception in real environments, including depth cues, environmental context, personal variables, and measurement methods.

Section 3: Getting Virtual: A First Overview
Description 3: Provide an initial overview of the differences in distance perception between real and virtual environments, mentioning empirical user studies and significant findings.

Section 4: Measurement Methods: Applying Virtual Psychophysics
Description 4: Describe the various methods used to measure subjective distance perception in virtual environments and discuss their applicability and results.

Section 5: Technical Factors: Constituting Virtual Environments
Description 5: Discuss technical factors affecting distance perception in virtual environments, such as hardware properties, nonpictorial depth cues, quality of graphics, and geometric distortions.

Section 6: Compositional Factors: The Reality Aspect in Virtual Environments
Description 6: Examine compositional elements of virtual environments that influence distance perception, including pictorial depth cues, avatars, familiar objects, virtual replicas, and transitional environments.

Section 7: Human Factors: Individual Influences and Differences
Description 7: Explore human factors affecting distance perception in virtual environments, including feedback, practice, adaptation, transfer effects, presence, and interindividual differences.

Section 8: SUMMARY
Description 8: Provide concluding remarks summarizing findings from all sections and suggest directions for future research.