Incidental Serial Reaction Time: Normal and Schizophrenic Response to the Onset and Cessation of Auditory Signals

Summary

This study tested the hypothesis that incidental serial reaction time (ISRT) latencies would be slower and more variable for schizophrenic than for normal Ss. It was predicted that the response of both groups to a manipulated stimulus dynamism would be proportionate, however, despite a difference in level of performance characterizing each sample. S responded to a series of 1000 Hz audiometric tones, signaling tone onset by pressure on a hand-switch, and offset by release. Thirty Ss without history of psychiatric disorder (16M, 14F) and 30 chronic schizophrenic patients (15M, 15F) were examined. All patients were drug-free and bore diagnoses of long standing. Signal tone length (1–3 sec) and interstimulus interval (1.5–15 sec) were varied randomly. Intensity levels were determined, in part, by reference to the individual threshold (T + 5, T + 35 db) and partly by prior selection of fixed values to be used with all Ss (10 and 40 db). Mean ISRT response was significantly slowed for the schizophrenic group, and these latencies were markedly more variable. Increased signal intensity reduced the latency of ISRT, significantly, in each group. The stimulus dynamism induced change in ISRT was altogether similar for both groups, over a range of 15–65 db. No evidence for a diminished vigilance from the beginning to the end of the experimental sitting was found, for either sample.