NEURAL MECHANISMS OF VISUAL PERCEPTION

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. We proposed experiments that test hypotheses about the neural mechanisms that underlie the brain's ability to make decisions. Our experiments address the mechanism used by the brain to convert sensory information represented by neurons in the visual cortex to a decision about what this information means for purposes of planning behavior. We showed that neurons in the association cortex of the macaque represent the accumulation of this evidence for one choice and against an alternative. This year, we demonstrated that the firing rate of these decision-making neurons conforms to the mathematics of diffusion, providing further support for their role in the process of noisy evidence accumulation (Churchland et al, 2011). We also showed how the mechanism incorporates prior knowledge about the more likely alternative affects the decision-making process (Hanks et al, submitted). We also discovered a mechanism for sensing and reproducing time intervals in humans (Jazayeri & Shadlen, 2010) and monkeys (Jazayeri & Shadlen, in revision). Decision-making bridges the gap between sensation and behavior. Nearly all non-reflexive behaviors require the brain to draw upon its sensory cortex to guide future behavior. Thus, the neural mechanisms for the simple decisions we study are likely to lend insight into more complex cognitive strategies. Our experiments ultimately furnish new insights into the causes and treatments of mental disorders affecting perception, planning and reasoning.