THE EFFECT OF STIMULUS-RESPONSE INCOMPATIBILITY ON P3 LATENCY DEPENDSON THE TASK BUT NOT ON AGE

To help identify the loci of age-related slowing of cognitive processi ng, the effects of stimulus-response (S-R) incompatibility and stimulu s degradation on P3 latency and reaction time (RT) were assessed in te n young and ten elderly women. Subjects saw the words right, left, RIG HT, or LEFT in tasks which required responses to (1) the meaning of th e word (WORD) (2) its case (CASE) and (3) both (CASE/WORD). Each task was tested with regular and degraded stimuli. On half the trials, the stimulus and response were incompatible. Although RTs and P3s of elder ly subjects were slower, especially RTs in CASE/WORD, stimulus degrada tion and S-R incompatibility did not differentially affect the two gro ups, suggesting that cognitive processing of older subjects is not esp ecially prolonged in perceptual and response-related stages. For both groups RTs and P3s were task dependent and were prolonged by degradati on and S-R incompatibility. Incompatibility delayed RTs in WORD and CA SE/WORD but P3s in WORD only. Thus, young and elderly subjects show qu alitatively similar psychophysiological and behavioral indicators of p rocessing speed.