Hemispheric Equivalence for Simultaneity Judgements of Somatosensory Stimuli

The capacity of the two cerebral hemispheres for temporal processing was investigated in a task requiring simultaneity judgement of pairs of tactile stimuli delivered unimanually or bimanually. Unimanual stimulation permitted presentation of both events to the same hemisphere while bimanual stimulation involved both hemispheres and necessarily required interhemispheric communication to compare stimulus onset asynchrony (S.O. A.). The order of presentation of asynchronous pairs determined which cerebral hemisphere was activated first. In each of two experiments, pairs of stimuli were judged as simultaneous at longer S.O.A.s in the bimanual than the unimanual conditions. Unimanual left and right simultaneity thresholds did not differ. These results suggest that the two hemispheres are equally capable of temporally resolving a pair of simple tactile stimuli. A structural model proposing that temporal comparisons are carried out in the hemisphere receiving the second stimulus provided the best account of the results.