Temporal integration of events within and between the cerebral hemispheres.

The effect of interhemispheric transmission time (IHTT) on temporal perception was investigated by comparing simultaneity thresholds under unimanual and bimanual stimulation conditions. In the unimanual conditions the tactile stimuli were delivered to the same hand and were received by the same hemisphere, but in bimanual conditions, where stimuli were delivered to different hands, interhemispheric communication was necessary in order to compare the timing of the two stimuli. Randomised order of stimulating the fingers of the hands was compared with consistent stimulation of each hand. Previous studies have used only consistent stimulation. Thirty-two undergraduate university students (16 males and 16 females) were tested. Bimanual simultaneity thresholds were significantly higher than unimanual. Previous research showing an absence of laterality effects for simultaneity judgements was confirmed, supporting a hemispheric equivalence model of temporal processing. Simultaneity thresholds were not affected by randomisation of stimulus location, indicating that expectancy effects were not responsible for the difference between bimanual and unimanual thresholds. The implication of these findings is that temporal perceptions are affected by the process of interhemispheric transmission.