Functional Imaging of the Human Visual System
摘要
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 the 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 6 other areas. The remaining human occipital areas either result from the 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 the 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). The anterior part of this complex is flanked by specialized regions devoted to processing faces and bodies. Together these ventral, temporal regions represent the shape of “visual objects” rather than image properties. While the ventral pathway codes the visual identity of objects, recent evidence indicates that the different dorsal stream regions code the visual identity of observed actions classes, as one of the information used by the parietal cortex in the planning of new actions.