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Constraints on perceptual decisions
Dr. Dov Sagi
Monday, March 06, 2006, 02:00pm - 03:00pm
The Weizmann Institute of Science Rehovot, Israel, Dept of Neurobiology, Brain Research
We study biases (decision criteria) observers have when reporting aboutvisual stimuli in conditions where more than one stimulus need to bedetected. We find that while with a single stimulus observers can varytheir decision criterion in an attempt to minimize their error rate,with multiple stimuli there are biases that reflect constraints ondecision making by the perceptual system. This can be accounted for byassuming that the brain can hold at any time only one internalrepresentation that corresponds to the statistical properties of thestimuli encountered within a given behavioral context. Thisunique-representation constraint may reflect the fundamentally unitarycharacter of phenomenal awareness: we can neither perceive nor respondto two stimuli as two independent events, but are compelled to integratethem into a single experience. This recasts the humbleresponse-criterion as a criterion for perceptual awareness. Cases inwhich awareness of selective stimuli is experimentally or pathologicallylost may thus be re-interpreted as a criterion shift.