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Active perception in humans

von Marleen Haupt

My research revolves around the topic of active perception in humans and is supervised by PD Dr. Kathrin Finke (General and Experimental Psychology, LMU) and Dr. Christian Sorg (Neuroimaging Center, TUM). The project is funded by a PhD research scholarship of the Elite Network of Bavaria and is carried out in collaboration with the DFG project "Active perception and functional connectivity in normal and pathological aging".

Active perception implies that perception is not solely a passive process leading to action, but that perceptual processing in itself can be influenced by expectations regarding incoming sensory inputs. According to the framework, anticipated information gets processed more efficiently than other inputs. Expectations can be formed based on numerous different factors. Most importantly for my research, expectations can also be modulated in behavioural experiments by implementing cues. Different cueing procedures can either alter bottom-up or top-down attentional processes.

In my first study, I use loud tones (comparable to warning tones in our environment like the siren of an ambulance) as bottom-up cues to induce short-term increases in the brain's general state of readiness, i.e. phasic alertness. If such alerting cues precede shortly presented visual displays with letters which have to be reported by the participants, the cueing leads to a significantly faster visual processing speed (measured in the number of items processed per second) compared to a baseline condition.

In my second study, spatial cues (bright frames around the location of an upcoming target letter) are implemented to investigate cueing effects on top-down attentional processes. The behavioural experiment, now consisting of red target and blue distractor letters, is split into different blocks. A block-wise modulation of the probability with which a spatial cue indicates the location of an upcoming letter enables us to address the question whether the brain can use expectations formed on probabilistic information to process percepts more efficiently. My study focuses on the effect of distractor probability cueing in displays with both, a distractor and a target letter, being present. Therefore, I manipulate the probability with which the distractor letter is being cued to investigate whether attentional weights for distractors decrease (and weights for targets increase) if our brain has the expectation that within a block of trials distractor locations are cued with a high probability compared to blocks with a lower probability. Indeed, our results show that distractors do not generally prevent us from perceiving targets. Instead, top-down expectations based on implicit probabilistic information can help us to shield against the distractor and perceive the target more efficiently.

Importantly, I am not only interested in active perception in younger healthy participants. My main research focus lies in active perception in healthy and pathological aging. Therefore, I am assessing healthy participants which are older than 60 years. The results of my studies show that, while general attentional capacities decrease over the lifespan, perception in healthy older participants can still benefit from the described modulations of expectations. These findings have important implications for every-day life situations of senior citizens. Firstly, seniors are regularly confronted with situation in which fast visual processing is required, e.g. traffic scenarios. In such scenarios, it is essential to be able to use warning signals in critical situations (e.g. the red lights of a car braking in front of you) in order to increase the brain's state of readiness short-term and, by that, process information more efficiently (e.g. what does the signal mean and how do I react appropriately). Secondly, the preserved ability to use probabilistic expectations to shield visual inputs from distractors is suggested to be useful in situations with a high amount of visual inputs, e.g. looking for a specific product in the supermarket. In this case, the expectation that distractors will be present in a certain location might potentially help senior citizens to perceive target objects better.

Overall, my research emphasizes that expectations can actively alter perception and that specific performance benefits based on expectation modulations are comparable in healthy aging. In a next step, I am investigating whether the behavioural effects in healthy younger and older participants can be explained by the same of differing underlying mechanisms. With this aim, I am relating the behavioural data to intrinsic functional connectivity networks based on resting-state fMRI data. Furthermore, I will test whether the described effects might be decreased or even absent in patients at risk for pathological aging and cognitive decline, e.g. Mild Cognitive Impairment. If this would be the case, the presented behavioural paradigms would be highly relevant for non-invasive and inexpensive clinical diagnostics.

With regard to potentially improving the differentiation between normal and pathological aging, I am also working on the standardisation and validation of a new cognitive screening tool (Oxford Cognitive Screening Plus) in a German sample. The cognitive screening has the advantage that it can be fully administered on a tablet and covers a wide range of cognitive functions. Standardised norms will allow the test administrator to judge which performance patterns can be explained by healthy aging or when the test results are being indicative of a risk for pathological changes.

Marleen Haupt

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