Functional imaging of the human visual system

Abstract

The human visual system consists of a large, yet unknown number of cortical areas. We summarize the efforts which have led to the identification of 19 retinotopic areas in human occipital cortex, using the macaque visual cortex as a guide. In this process retinotopic mapping has proven far superior to the study of functional properties. Macaques and humans share early areas (V1, V2, and V3), a motion-sensitive middle temporal (MT/V5) cluster as well as six other areas. The remaining human occipital areas either result from reorganization of a group of monkey areas or seem to be specifically human. Several regions sensitive to motion and even higher-order motion have been described in parietal cortex, the retinotopic organization of which is still under debate. On the other hand, both dorsal and ventral regions are sensitive to shape, which is most pronounced in the lateral occipital complex (LOC) extending into the fusiform gyrus. The anterior part of this complex is flanked by specialized regions devoted to processing faces and bodies and represents “visual objects” rather than image properties. Its exact organization requires further investigation.