Effect of luminance on successiveness discrimination in the absence of thecorpus callosum

Three split-brained subjects, one with full forebrain commissurotomy and tw o with callosotomy, were impaired at judging whether pairs of lights in opp osite visual fields were successive or simultaneous. This impairment did no t vary with luminance when the lights were grey against a dark background, but was more pronounced when the lights were equiluminant with a yellow bac kground. All three subjects were also better able to discriminate successio n fr-om simultaneity when the lights were both in the left visual field tha n when they were both in the right. A fourth subject with callosal agenesis was only slightly impaired relative to normal subjects, who were virtually errorless. (C) 2000 Elsevier science Ltd. All rights reserved.