Sequential effects in two-choice reaction time: Subjective expectancy and automatic after- effect at short response-stimulus intervals

Between three serial two-choice reaction-time tasks, the response-stimulus interval (RSI), stimulus-response compatibility, and practice were varied in order to examine two determinants of sequential effects — subjective expectancy and automatic aftereffect. It appears that subjective expectancy is absent when the RSI is below a critical minimum. In an incompatible task, however, this minimum is greater. This is interpreted in support of the single-channel hypothesis: the subject only builds up expectancies when the “central processor” is unoccupied. The automatic aftereffect increases as the RSI decreases. The decay of the aftereffect seems to take place mainly during the RSI and only to a minor degree during the reaction process. Normally, a strong aftereffect operates in a general way, but after extensive practice it becomes stimulus specific. A model is presented, which assumes that only at the initial stages of practice is the unused “neural pathway” inhibited each time the stimulus is an alternation.