Foreperiod duration and the timecourse of preparation

Abstract

There is a clear conflict in the literature between studies which report a reduction and those which report a delay of reaction time to a signal (S 2), which is just preceded by a non-informative signal (S 1). The hypothesis is tested that these diverging results are due to the size of the foreperiod (FP) between a warning signal (W) and S 1. In the first experiment S 1 and S 2 were both visual, while S 1 was auditory and S 2 was visual in the second experiment. With two visual signals a delay was found at FP of 1 sec and a reduction at FP of 5 sec, provided that the interval between S 1 and S 2 (ISI) exceeded 150 msec. Insertion of S 1 just before arrival of S 2 virtually eliminates the traditional foreperiod effect. The latter result was also obtained in the second experiment. When S 1 is auditory, the reduction of RT at FP of 5 sec is found at much shorter FPs, and no delay at FP of 1 sec is observed. The results are explained most readily by a preparation theory, which assumes that the speed of preparatory adjustment is variable.