Visual areas and spatial summation in human visual cortex

Functional MRI measurements can securely partition the human posterior occi pital lobe into retinotopically organized visual areas (Vl, V2 and V3) with experiments that last only 30 min. Methods for identifying functional area s in the dorsal and ventral aspect of the human occipital cortex, however, have not achieved this level of precision; in fact, different laboratories have produced inconsistent ri pol-ts concerning the visual areas in dorsal and ventral occipital robe. We report four findings concerning the visual r epresentation in dorsal regions of occipital cortex. First, cortex near are a V3A contains a central field representation that is distinct from the fov eal representation at the confluence of areas V1, V2 and V3. Second, adjace nt to V3A there is a second visual area, V3B, which represents both the upp er and lower quadrants. The central representation in V3B appears to merge with that of V3A, much as the central representations of V1/2/3 come togeth er on the lateral margin of the posterior pole. Third, there is yet another dorsal representation of the central visual held. This representation fall s in area V7, which includes a representation of both the upper and lower q uadrants of the visual field. Fourth, based on visual field and spatial sum mation measurements, it appears that the receptive field properties of neur ons in area V7 differ From those in areas V3A and V3B. (C) 2001 Elsevier Sc ience Ltd. All rights reserved.