Automatic aftereffects in two-choice reaction time: a mathematical representation of some concepts.

A mathematical model is developed to describe sequential effects in two-choice reaction time experiments with a short response-stimulus interval. Evidence is briefly discussed that in conditions with short response-stimulus intervals, automatic aftereffects dominate sequential effects, and the influence of subjective expectancy can be neglected. In these conditions the model premises three components of automatic aftereffects--facilitation, inhibition, and noise, with a common decay factor. Influence of response-stimulus interval and practice on sequential effects are examined and related to parameter changes in the proposed single-decay model. The decrease of automatic aftereffects with increasing response-stimulus interval is primarily ascribed to an increasing decay factor. The parameter representation of the model also clarifies the issue of the disappearance of automatic aftereffects with practice. It shows a gradual fading of inhibition in the initial stages of practice, together with a slower decrease of the facilitation effect. The single-decay model provides a satisfactory explanation for the processes involved in compatible two-choice reaction time with short response-stimulus interval.