Expectancy for events in old age: stimulus sequence effects on P300 and reaction time.

Event-related brain potentials were collected from 10 young (M = 22 years) and 10 elderly (M = 77 years) women. Stimuli were random sequences of 1000- and 1500-Hz tone pips in a two alternative, forced choice, reaction time task. Trials were sorted and averaged according to the sequence of the preceding four tones: continuations of repetitions (AAAAA) and alternations (ABABA) and discontinuations of repetitions (BBBBA) and alternations (BABAA). For both groups the P300 component of the event-related brain elicited larger P300s than did discontinuations of alternations, an effect especially large for the elderly women. Mean reaction time did not differ between the two groups, although P300 latencies were significantly longer for the elderly group. Results are discussed in terms of age-related differences in response strategies and sensitivity of P300 latency to response strategy.