| Abstract: | A group of 12 young adults were subjects in two separate experiments. In the first experiment subjects listened to 71 dB clicks presented in stimulus sequences consisting of a single click and a pair of clicks. Interspersed at random among these loud clicks were soft clicks—singles and pairs of clicks—which subjects were required to detect and respond to by pressing a button. Average evoked potentials (AEPs) to the second click of the pairs of loud clicks were investigated as a function of the interstimulus interval (ISI), which had values of 50, 100, 250, 500, 750, and 1,000 msec distributed at random. In the second experiment, similar sequences of clicks were used. Single clicks were soft clicks, pairs of clicks were loud clicks, and subjects were required to respond as quickly as possible to the second click of each pair. Reaction time (RT) was investigated as a function of the ISI, which varied as in the first experiment. Both the latency of the P1 and P2 components of the AEP and the RT were found to increase with decreasing ISI. These results were statistically significant at the .01 level of confidence. Analysis of covariance suggested that the latency differences in P1 associated with ISI could account for nearly half of the RT variance due to ISI. Findings suggest that latency differences in the P1 component of the AEP may provide a physiological basis for the delays known as the psychological refractory period which occur in the processing of closely-spaced stimuli. |
