Functional Imaging of the Human Visual System

The human visual system consists of a large, yet unknown number of cortical areas. We summarize the efforts made to identify these areas, using the macaque visual cortex as a guide. So far, retinotopic mapping has identified several regions and study of functional properties such as motion and shape has revealed further expanses of visual cortex. Macaques and humans share early areas (V1, V2, and V3) and a motion-sensitive middle temporal (MT/V5) region, but the intervening cortex has considerably developed in humans with the appearance of new areas. The kinetic occipital region is located in this part of cortex between V3A and the human MT/V5 complex. Several regions sensitive to motion and even higher order motion have been described in parietal cortex. 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 represents visual objects rather than image properties.