The effect of conditional probability of the response signal on the simple reaction time

Abstract

With simple reaction time schedules using irregular series of interstimulus intervals (or preparatory periods), the relationship between the response latency and the duration of interstimulus intervals depends on two factors: (1) Time uncertainty increasing when time estimation is made more difficult by lengthening the interval duration. (2) Probability of signal occurrence, increasing with time (conditional probability). In order to investigate the role of the latter factor time uncertainty has been made equal for all time intervals by introducing a second signal with a periodicity equal to a sub-multiple of the duration of the different intervals. It is shown that the responses latency is inversely related to the duration of the interstimulus intervals; this relationship is absent in a control experiment where the second signal is not given. The worsening of the average performance is explained in terms of probability, the role of a differential learning in the two situations is discussed and the exact shape of the curves is analyzed.