Interhemispheric comparisons in a man with complete forebrain commissurotomy

J. Sergent (1991) claimed that split-brained people are highly accurate in judging which is the larger of 2 circles in opposite visual hemifields but are relatively poor at judging whether circles in the 2 hemifields are of the same size. The discrepancy could be due, at least in part, to an artifact. A split-brained man, L.B., was markedly worse than normals at judging which was the larger of 2 circles or the longer of 2 horizontal lines in opposite hemifields, and his performance could be largely accounted for without assuming any interhemispheric transfer. L.B. also judged whether a single flashed line extended further into the left or right hemifield and, as in a previous study (M. C. Corballis, 1995), was strongly biased to respond "right longer." This bias was not observed in the judgments about the circles or the separated lines, suggesting that it is not due to a compression of perceived space in the left hemifield.