Stimulus probability and motor response in young and old adults: An ERP study.

Investigated effects of responding hand and stimulus probability in 24 young males (aged 18-24 yrs) and 24 old males (aged 67-75 yrs) subjects in a reaction time (RT) task in which both rare and frequent stimuli required a response. The effect of stimulus probability was less pronounced in old Ss than in young, and the latency of P3 potentials was longer in the elderly, although their RTs were not different from young Ss. Event related potentials (ERPs) for right hand responses were larger than for left hand responses; this difference was discernible already in the P2 and N2 peaks of the ERP. A tentative explanation is offered for these large and unexpected hand differences. An interpretation in terms of an age-related decrease in resources is proposed for the increased P3 latency and the decreased probability effect on P3 amplitude in old Ss.