Figure 5.

Preferential activation of human V1 produced by alternating stimulus contrast. A shows the contrast gain function based on averaged MR time courses from three visual cortical areas: V1, V3, and MT (5). The data predict that stimulus alternation between 6% and 100% contrast should produce robust MR modulation (80% maximum) of V1, but essentially no modulation in MT and V3. C shows the result of this experiment. Significant activation (red through yellow) is largely confined to area V1. Area borders in C have been transposed from field sign tests from the same subject, shown in B. To minimize cortical distortion, area V1 has been artificially bisected (as in refs. 5 and 12).