FUNCTIONAL-ANALYSIS OF V3A AND RELATED AREAS IN HUMAN VISUAL-CORTEX

Using functional magnetic resonance imaging (fMRI) and cortical unfold ing techniques, we analyzed the retinotopy, motion sensitivity, and fu nctional organization of human area V3A. These data were compared with data from additional human cortical visual areas, including V1, V2, V 3/VP, V4v, and MT (V5). Human V3A has a retinotopy that is similar to that reported previously in macaque: (1) it has a distinctive, continu ous map of the contralateral hemifield immediately anterior to area V3 , including a unique retinotopic representation of the upper visual fi eld in superior occipital cortex; (2) in some cases the V3A foveal rep resentation is displaced from and superior to the confluent foveal rep resentations of V1, V2, V3, and VP; and (3) inferred receptive fields are significantly larger in human V3A, compared with those in more pos terior areas such as V1. However, in other aspects human V3A appears q uite different from its macaque counterpart: human V3A is relatively m otion-selective, whereas human V3 is less so. In macaque, the situatio n is qualitatively reversed: V3 is reported to be prominently motion-s elective, whereas V3A is less so. As in human and macaque MT, the cont rast sensitivity appears quite high in human areas V3 and V3A.