Much effort has been invested in exploring the basis of mammalian visual pattern perception. Another important visual function that has received far less attention is visual analysis during locomotion. The goal of this proposal is to study this function using single cell recording methods in the cat. The cat is a good model for three reasons. Its visual system in many respects resembles that of primates. Like humans, the cat is basically terrestrial, and thus must solve similar problems during locomotion. Moreover, extensive evidence suggests that one area of the cat's extrastriate cortex, the lateral suprasylvian area (LS), may play a major role in vision during locomotion. A novel visual display system has been developed, based on a Next computer, in order to present stimulus displays that simulate the visual scene during locomotion. The display is large, subtending about 60 degrees horizontally, so as to adequately stimulate the very large """"""""silent surrounds"""""""" typical of cells in LS. A wide-field version of the display will be used to ask how a cell's response to a moving stimulus is affected by placing the stimulus in the context of an optic flow field, and how manipulation of different parameters of the optic flow affect cell responses. A smaller version of the display, containing a high density of moving images, will be used to ask whether cells respond to stimuli that differ from their neighbors, and might represent obstacles or irregularities in terrain. The same displays will be used to test responses in area 19, an extrastriate area that has connections very similar to those of LS, but that has quite different response properties. The hypothesis is that responses in area 19 to optic flow simulations will be poor or non-specific since its response properties do not suggest any role in visual analysis during locomotion. The source of the large """"""""silent surrounds"""""""" in LS, which may contribute to analysis of optic flow fields, will be examined with two approaches. The major thalamic input to LS will be removed, since the response properties of this input suggest that it is a likely source of wide-field effects. Response properties in LS will then be tested. Intrinsic connections within LS will be studied to see whether their distribution can be explained on retinotopic grounds, or instead might contribute to wide- field inhibition and/or facilitation. This project will fill a major gap in our understanding of visual function at the level of single cell behavior. Ultimately, a clear understanding of normal visual cortical function will provide insight into the underlying causes of visual dysfunction resulting from damage to the cerebral cortex.
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