Information processing and interhemispheric transfer in left- and right-handed adults.

Two experiments are reported using simple reaction time (SRT) and visual evoked potentials (VEP) to measure information processing and interhemispheric transfer time (IHTT) in left- and right-handed subjects. Study 1 used an SRT procedure to estimate IHTT in 30 left-handed and 30 right-handed subjects. No differences in IHTT were indicated, but left- and right-handers were found to have opposite visual field advantages on the SRT task, indicating possible hemispheric differences in visual information processing. Study 2 was designed to test hypotheses generated in Study 1, using a VEP procedure to provide additional measures of visual information processing and IHTT. VEPs were collected during an SRT procedure in 20 left-handers and 20 right-handers, and SRT response hand and visual field advantages were replicated among right-handers only. Left-handers in Study 2 demonstrated no significant response hand or visual field effects on SRT. Analysis of the VEP N160 latency data indicated no significant laterality, hemisphere, or visual field effects, except for a robust hemisphere by visual field interaction, which reflects IHTT. The significant SRT left visual field advantage in right-handers was not reflected by hemispheric asymmetries in VEP N160 latency. It is concluded that left-handers and right-handers do not differ in IHTT in two functional regions of the corpus callosum, nor do they vary in simple visual receptive processing. Results are more consistent with variability in SRT resulting from differences in complex heteromodal processes beyond the striate and extrastriate visual cortex.