Interhemispheric visual matching in the split brain.

Three split-brained subjects, one (N.G.) with full forebrain commissurotomy and two (V.P. and J.W.) with callosotomy, made same-different judgments about pairs of visual stimuli that were flashed either unilaterally or bilaterally. In separate blocks of trials, the stimuli could differ in luminance, size, or color. In the bilateral condition, only J.W. scored above chance, and only minimally, on the luminance and size tasks, and none of the subjects scored above chance on the color task. Accuracy was generally much higher, especially for V.P. and J.W., when the stimuli were unilateral. These results confirm that there is little or no interhemispheric transfer of the visual attributes of luminance, size or color in the split brain.