Hemisphere-hand interactions for the matching of letters

Young, middle aged, and older subjects were given a Posner-type physical-name matching task, in which stimuli were presented to one or both hemispheres, and a simple discrimination reaction time (DRT) task. Reaction time differed between young and middle aged groups for both tasks with shorter RT for the DRT task. Reaction time for the older group did not differ significantly from that of the middle aged group for either task, although the reaction time for the older group was longer. Reaction time was faster for all age groups when Stimulus 1 and Stimulus 2 were presented to different hemispheres for the matching task than when both stimuli were presented to the same hemisphere. Ipsilateral finger responses (hand relative to hemisphere) were slower than contralateral responses but this was true only with regard to the visual field of presentation for stimulus 2. These data indicate that sharing of information between hemispheres under certain circumstances increases the efficiency of information processing relative to that observed with unilateral visual half-field (hemisphere) presentations and that hand or finger response relative to visual field of presentation is an important factor which must be controlled and examined relative to visual field of presentation.