Sequential effects in two-choice reaction time: automatic facilitation or subjective expectancy?

A repetition effect is said to occur in a two-choice reaction time (RT) task when the RT for a repeated signal or response is faster than the RT for a new signal or response. An alternation effect is said to occur when the RT for a new signal or response is faster than for a repeated signal or response. A change from a repetition effect to an alternation effect was found across three response-stimulus intervals ranging from 50 msec to 2,000 msec. An analysis was also carried out of the higher-order sequential effects. Differences were found between those obtained from a repetition effect and those obtained from an alternation effect, suggesting that different factors operate in producing them. Two further experiments examined the roles of subjective expectancy and an automatic facilitation in determining these effects. Results suggested that while subjective expectancy operates at all response-stimulus intervals, an automatic facilitation operates only at short intervals.