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.

The P300 component of the event-related brain potential as an index of information processing.

Studies of event-related brain potentials (ERPs) have shown that attributes of the ERP can be used as dependent variables in the study of human information processing. These variables can complement the information gained from the study of overt, skeletal responses. The manner in which the P300 component of the EPR can be used to study human information processing is illustrated in this report. Specifically, we show that through an analysis of the covariation of the latency of P300 component and reaction time, it is possible to examine the relation between the probability of a stimulus and the speed of response to that stimulus. Our data indicate that increased in the probability of a stimulus reduce reaction time by decreasing both stimulus-evaluation and response-production times. We also examine changes in reaction time and P300 latency induced by the match or mismatch between two stimuli presented consecutively, again as a function of probability. Models of the effects of stimulus matching on reaction time are evaluated.

Attention and cardiac activity: heart rate responses during a variable foreperiod, disjunctive reaction time task.

A variable foreperiod disjunctive reaction time task was used to evaluate the effects of stimulus discriminability on cardiac activity. In two sessions, 20 male undergraduates received easy or difficult auditory discrimination trials in blocked and random series. In the random session only, when the warning stimulus provided information about the difficulty of the subsequent discrimination, difficult trials were associated with greater foreperiod deceleration. Cardiac accelerations also tended to be greater in the foreperiods of difficult trials. There was an effect of both warning and imperative stimuli on the heart rate of the cycle in which the stimuli occurred which depended on the difficulty of the trial. The results are discussed in terms of the psychological significance of the different heart rate responses.