In a simple manual reaction time task, reaction times are longer if the responding hand and visual field of the stimulus are contralateral than when the hand and field are ipsilateral. This small crossed vs. uncrossed difference (CUD) has often been attributed to the interhemispheric transmission time incurred when the hemisphere receiving the sensory input is not the one initiating the motor response. We assessed the generality of the visual CUD by comparing it to the CUD for tactile stimuli. Visual and tactile CUDs did not differ significantly in magnitude, and in both modalities the CUD showed a strong asymmetry, with a positive CUD occurring only for the left hand. This outcome indicates that the properties of the visual CUD are not determined by neural pathways, or hemispheric asymmetries, that are specific to the visual system.
Adult Afferent Pathways