Representation of space is essential for reaching and grasping, orienting and navigating, and for reasoning about interactions among objects and organisms in the world. It is therefore of great importance to understand the neural basis of spatial representation in the brain. A possible clinical benefit of such knowledge would be an improved ability to interpret neurological insults. A profoundly influential idea in visual neuroscience is that there are two discrete cortical processing streams: a spatial processing stream that terminates in parietal cortex and an object processing stream that terminates in inferotemporal cortex. Recently, we have discovered evidence of spatial processing in the inferotemporal pathway, hitherto believed specialized for object recognition. This proposal is designed to investigate the hypothesis that spatial information is a common property of both the parietal (dorsal) and inferotemporal (ventral) visual cortical processing streams. Because there has been little physiological study of the inferotemporal pathway's role in spatial representation, my research focuses on the implications of this question: first, by studying the role of gaze-dependent modulation of visual cortical responses; and second, by evaluating the contribution of binocular information to spatial representation. The first objective is to study the role of extraretinal signals related to gaze direction and distance on the responses of inferotemporal stream neurons in awake macaque monkeys. In particular, since spatial scaling (size constancy and stereo depth constancy) use gaze distance information, we shall examine how gaze position influences the responses of size-selective and disparity-selective neurons in areas V1, V2, and V4. There are three known classes of binocular visual information that humans can exploit for distance discrimination and scaling: horizontal disparity, differential occlusion, and differential perspective (the horizontal gradient of vertical disparity). Only the neural basis of horizontal disparity has been explored to date. The second objective is to examine the sensitivity of inferotemporal stream neurons to differential binocular occlusion, and the third objective is to investigate the sensitivity of inferotemporal stream neurons to differential perspective.
