Hemispheric equivalence and age-related differences in judgments of simultaneity to somatosensory stimuli.

Hemispheric asymmetries, interhemispheric transfer time (IHTT), and age-related differences in judgments of simultaneity to tactile stimulation were examined. Two mechanical stimulators were employed to: (1) Determine whether both cerebral hemispheres are equally capable of processing fine tactile temporal information; (2) determine whether there is an age-related differential hemispheric decline in judgments of simultaneity, and (3) determine if simultaneity thresholds for tactile stimuli increase with advanced age. Tactile simultaneity thresholds were measured by using a modified parameter estimation by sequential testing algorithm. Participants judged whether pairs of tactile stimulation to index and middle fingers were delivered simultaneously. Results of both bimanual and unimanual conditions supported a model of hemispheric equivalence in that both hemispheres were equally capable of making judgments of simultaneity to fine tactile stimuli. The results further suggested that the hemispheric equivalence for judgments of simultaneity remains stable across adulthood. However, IHTTs of older adults were more than double that of younger adults, indicating a significant decrease in the speed of neural conduction. As well, relative to younger adults, older adults had significantly higher simultaneity thresholds.