Toward a Neural Understanding of Visual Surface Representation

Owing to the exploitation of available techniques in modern neuroanatomy and neurophysiology, an increasingly detailed picture of the primate cortical visual system is emerging. First, a topographic map of the retina appears to be duplicated many times in the cerebral cortex (Hubel and Wiesel 1965; Zeki 1978), and more than a dozen separate cortical maps of the retina have been described (Maunsell and Newsome 1987). Second, there seems to be a set of parallel anatomical pathways mediating visual function. This segregation begins as early as the retina and appears to continue through many cortical areas. Segregation is manifested particularly in the responses of individual cells. Cells differ in their selectivity to various characteristics of the visual image: binocular disparity, line orientation, motion direction, size, color, etc. (for review, see Livingstone and Hubel 1987).