SEQUENTIAL OPERATION OF DISCONNECTED CEREBRAL HEMISPHERES IN SPLIT-BRAIN PATIENTS

WHEN two concurrent sensorimotor tasks require separate responses, sel ection of the first response generally delays selection of the second. Dual-task performance was examined in four patients who had undergone surgical transection of the forebrain commissures including the corpu s callosum. One light flash was presented to each visual field in succ ession, and patients made a choice response to each stimulus with the ipsilateral hand, thereby confining the tasks to separate hemispheres. All four showed dual-task interference very similar to that found wit h normal individuals. Therefore, still-intact subcortical structures m ust play a critical role in sequencing response selection processes (t he 'dual-task bottleneck'), confirming the distinction between the att entional limitations involved in planning actions and those involved i n perceptual analysis.