Response time to the second of two signals following varied vs constant intersignal intervals

The Ss made choice responses under three experimental conditions: (1) a variable interval between the warning signal and the signal to respond, (2) a constant interval between the warning signal and the signal to respond, and (3) omission of the warning signal. With variable intersignal intervals (lSI), response time (RT) was inversely related to lSI at least when the latter was in the 10 to 225 msec range. When lSI was constant its duration had no perceptible effect on RT. RT tended to be shorter with constant lSI. independent of its duration, than when the warning signal was omitted altogether.