Curvature in Depth for Object Representation

Abstract

Until recently, it had been widely understood that information in the primate visual system is distributed into two main pathways, dorsal and ventral, to achieve two main goals. Motion and spatial information flow into the dorsal pathway to be used for control of movements, while the shape, color, and texture information flow into the ventral pathway for identification of objects. Images of an object fall on slightly displaced locations of the left retina and right retina due to the horizontal separation of the two eyes, and this disparity can provide the position of the points in depth (see figure). The disparity information has been frequently found in cells at various stages in the dorsal pathway, but not very often in cells in the ventral pathway. Cells with selectivity for disparity constituted 70%–80% of cells in the thick cytochrome oxidase (CO) stripes of V2 and in MT along the dorsal pathway, while only 20%–30% of cells in the thin and pale CO stripes of V2 and in V4 along the ventral pathway showed such selectivity (DeYoe and Van Essen 1985). It was tempting to conclude that disparity depth information is mainly used as a spatial cue in the primate brain, as cells with disparity selectivity were mainly found in the dorsal pathway. However, by recording single-cell activities from passively fixating monkeysJanssen et al. 2000a, Janssen et al. 2000b( [this issue of Neuron]) and Uka et al. 2000 have found many cells in the inferotemporal cortex selectively responding to stimuli with disparity. Together with another set of recent findings that many cells in the parietal cortex selectively respond to particular complex 2-dimensional shapes (Sakata et al. 1997; Sereno and Maunsell 1998), the dorsal versus ventral dichotomy is now less distinct than it was thought to be previously.Figure 101Disparity Gradient on the Retina Due to Depth Gradient of a Surface