High order sequential effects and the negative gradient of the relationship between simple reaction-time and foreperiod duration.

In a simple RT task with variable interstimuli intervals (ISI), the negative slope of the RT-ISI duration relationship is generally interpreted as an effect of the increasing conditional probability of the response signal (RS). A previous study using 6 different ISIs has shown that the first order sequential effects (SE) contribute, for a part, to this slope. The aim of the present experiment was to investigate, up to the fifth order, the SEs observed when two different ISIs (1.5 and 3.0 sec) are used. The results show that SEs also intervene in the tendency for the Ss to be preferentially prepared when the RS occurs at the end of the long ISIs. They are discussed according to the hypothesis that the role played by these SEs in the negative slope of the RT-ISI relationship is primarily due to the opportunity given the Ss in such an experiment to make two successive preparations.