12 Chronometric Analysis of Human Information Processing

The covariation of P300 latency and reaction time was assessed in two sets of experiments designed to test the hypothesis that P300 latency reflects a subset of the information processes whose durations are reflected in RT. In the first experiments, P300 latency and RT were shown to covary as a function of the time required to categorize a stimulus. However, this relationship could be dissociated by requiring subjects to make highly speeded responses which also resulted in increased error rates. In the second experiments two factors, stimulus discriminability and stimulus-response compatibility, were shown to have additive and independent effects upon RT. The latency of P300 was strongly affected by stimulus discriminability but only minimally affected by S-R compatibility. These results are interpreted to support the hypothesis that P300 latency reflects primarily the durations of processes concerned with stimulus evaluation and is relatively unaffected by processes concerned with response selection and execution.