The refractory period of choice reactions with regular and irregular interstimuli intervals.

Abstract On each trial, two successive choice reactions, each a two-choice one, had to be given to visual stimuli. The stimuli were separated by time intervals (ISIs) ranging from 0 to 500 msec which were presented in both a predictable (regular condition) and an unpredictable way (irregular condition). Efforts were made, through instructions and the provision of knowledge of results, to have the Ss give priority to speed in the first reaction. Six Ss gave more then 2000 trials each, in ten successive sessions. No tendency to wait for the second stimulus was observed. Clear delays, negatively correlated with ISI duration, were observed in the second reaction at short ISIs, with both predictable and unpredictable ISIs. Time uncertainty is thus not a necessary condition for the production of such delays. The relationship between RT2 and the interval between the arrival of the second signal and the end of RT1 suggest: (a) that the central mechanisms are occupied by the first reaction for a time which lasts longer than RT1, which is in agreement with Davis' suggestion of a central recovery time; (b) that this central recovery time is variable; (c) that the occupation by the first reaction is not total, and that some residual capacity is still available during the refractory period to deal with the second signal.