International Journal of Comparative Psychology

The capacity of the two cerebral hemispheres for temporal processing was investigated in two experiments concerned with sensory and motor processing, respectively. The temporal processing of sensory information was examined 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 (SOA). The order of presentation of asynchronous pairs determined which cerebral hemisphere was activated first. Pairs of stimuli were judged as simultaneous at longer SOAs in the bimanual than the unimanual conditions whilst 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 provides the best account of the results.

The temporal processing of motor information was examined in a task requiring the planning and execution of sequences of finger movements. A predetermined number of double-tap responses with the index and middle fingers of a given hand were required in response to a visual cue in the ipsilateral visual field. The restriction of the performance cue in each trial to the hemisphere controlling the response permitted assessment of the contribution of each cerebral hemisphere to differences in hand skill. Movement time increased linearly for both hands with increasing length of tap sequence and did not differentiate hand performance. Response preparation time, however, increased linearly with increasing task load for the preferred hand but varied quadratically for the non-preferred hand. These results indicate that differences in hand skill may be determined by the mode of response preparation within the contralateral hemisphere. They also suggest that studies of hand differences involving fixed levels of motor demand would not properly differentiate hand performance.

Together, these studies indicate that both cerebral hemispheres are capable of the temporal processing of sensory and motor information but that the hemisphere primarily involved is determined by side of stimulus or response, respectively.