ROLE OF THE COMMISSURES IN INTERHEMISPHERIC TEMPORAL JUDGMENTS

A man who had undergone forebrain commissurotomy (L.B.) and a man with agenesis of the corpus callosum (R.B.) judged whether pairs of spatia lly separated lights were successive or simultaneous. Stimulus onset a synchronies (SOAs) were 0, 17, 33, 50, 67, 83, 117, and 150 ms. When t he lights were in opposite visual fields, the SOA at which the discrim ination first reached a level significantly above chance was 150 ms fo r L.B., 67 ms for R.B., and 33 ms for ''normal'' participants. Results parallel evidence from reaction time studies in which estimates of in terhemispheric transfer time for callosal agenesis patients Lie betwee n those of normal controls and those with surgical section of the fore brain commissures. L.B, also showed a left-visual-field deficit in the discrimination, though it was less marked than his deficit with bilat eral presentations.