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Chapter 5&6

Chap.5 & 6

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Western University
Psychology 1000
Terry Biggs

Chapter 5Sensation and Perceptiony Sense organs allow us to experience light waves brightnesses and colours air vibrations sounds and chemical substances odours or tastesy Sensationthe stimulusdetection process by which our sense organs respond to and translate environmental stimuli into nerve impulses that are sent to the brain y Perceptionactive process of organizing the stimulus input and giving it meaning Making sense of what our senses tell usSensory impaired people who have the problem of mixing their sensesSynaesthesiay Eg Experience sounds as colours or tastes as touch sensationsy Women are more likely to be synaesthetesy Maurer and colleagues suggested that we are all born synaesthetic because as an infant we had neural pathways that were all undifferentiated and could lead to crossmodal perceptionsy Cross wiring is usually what causes synaesthesia Therefore activity in one part of the brain evokes responses in another part of the brain dedicated to another sensory modalityy Some say that it occurs in people that do not undergo the process of breaking their neural connections which usually occurs in infancy Therefore the brain ends up retaining all these connections that should be absent later on in lifey Others say that it is caused because the person has a deficit in neural inhibitory processes in the brain that is suppose to keep input from one sensory modality from overflowing into other sensory areasy Binding problem a big question in cognitive neuroscience that focuses on how we bind all our perceptions into one complete whole experience while still being able to keep its sensory elements apart Transduction y Occurs when stimuli activate specialized sensory receptorsy Our sensory receptors translates stimuli into nerve impulses the language of our nervous systemstimuli can be light sound waves chemicals pressure or anything else y Feature detectors specialized neurons break down and analyze the specific features of the stimuli y These stimulus pieces are then reconstructed into a neural representation that is compared with previously stored information in our brain ie our knowledge of what a particular object looks smells or feels like and forms a perceptiono Eg when you hold a rose in your hand and feel the petals smell its aroma your sensory experiences come together and form a total experience about how you feel about the rose However people who are synaesthetic create additional perceptions of the rose that are usually inaccurate Sensory Integration summaryy Sensation is present y Stimulus is received by sensory receptorsy Receptors translate stimulus properties into nerve impulses transductiony Feature detectors analyze stimulus featuresy Stimulus features are reconstructed into a neural representationy Neural representation is compared with previously stored information in the brainy Matching process results in recognition and interpretation of stimuliy Perception is made Sensory Processes y Your brain can understand the outer world because of sensor receptors that transform sensory information from the outside world into the code language of nerve impulsesy Psychophysics the study of how physical stimuli are translated into psychological experience and is concerned with 2 types of sensitivityo Absolute limits of sensitivity what is the softest sound or weakest salt solution humans can detecto Differences between stimuli how much difference must there be between two tones before we can tell they are identical y Stimulus detectionabsolute threshold designated as the lowest intensity at which a stimulus can be detected 50 of the time o The lower the absolute threshold the greater the sensitivity 1y Signal detection theoryconcerned with the factors that influence sensory judgments The concept of a fixed absolute threshold is inaccurate because there is no single point on the intensity scale that separates nondetection from detecting a stimuluso Decision criterionstandard of how certain a person must be that a stimulus is present before they will say they detect it This decision criterion can change from time to time depending on fatigue expectation and the potential significance of the stimuluso Single detection shows us that perception is in part a decisiono Increased rewards for noticing stimuli often results in lower detection thresholds o Increased dangerpunishment for noticing stimuli often raises detection thresholdy Subliminal stimulus a stimulus that is so weak or brief that although it is received by the senses it cannot be perceived consciously well below the absolute thresholdo Can still affect attitudes and behaviors without us knowing ito James Vicary 1950 flashed subliminal messages Drink Coke and eat popcorn and saw that people bought more of ito Can they affect attitudesKrosnick study 1992Showed nine slides of different people followed by unpleasant messages and found that the people showed negative attitudes towards the pictures that had negative subliminal messageso Research findingslittle effect on behaviouronly small effect on attitudesy Difference thresholdsmallest difference between two stimuli that can be perceived 50 of the time just the noticeable differencejnd o Weber said that there is some degree of lawfulness in the range of sensitivities within our sensory systemso Webers Lawstates that the difference threshold or jnd is directly proportional to the magnitude of the stimulus that the comparison is being made witho According to Webers Law this can be expressed as a Weber fractionValue for weights150 therefore if 50 lbs is lifted increased weight will only be detected at 51 lbs y Eg if you lift a weight of 50 grams the other weight must weigh at least 51 grams for the comparison to be made If you lift a weight of 500 grams the other weight must be at least 510 grams for a comparison to be made 150 10500 The smaller the fractionthe higher the sensitivityDoesnt apply to extremely high or low stimulation intensitiesaudition tonal pitch1333vision brightness160pain heat reduces130audition loudness120taste salt concentration13 y some senses are more sensitive than others hearing more than tastey Sensory adaptationthe diminishing sensitivity to an unchanging stimulus o Perception of stimuli will decrease if constantly present o Adaptation habituation occurs everyday Eg monotonous background sounds are largely unheard Eg the feel of a watch on our hand eventually decreases from our awareness Eg when you dive into a swimming pool the water may feel cold at first because your bodys temperature sensors respond to the change in temperature but eventually you adapt to the new temperature because your sensory neurons diminish their sensitivity to the unchanging stimulus so that you stop feeling as coldo Although sensory adaption reduces our overall sensitivity it is adaptive because it frees our senses from the constant and ordinary to be able to pick up informative changes in the environmento Survival value attend to a new stimuli in the environment2
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