Expectancy or Automatic Facilitation? Separating Sequential Effects in Two-Choice Reaction Time

Two concepts have been proposed to explain sequential effects in serial reaction time, namely, automatic facilitation and subjective expectancy. The present study clarifies the relation between these concepts and specific data patterns obtained in a two-choice task. The proposed repetition-alternation function is particularly suited to distinguish the benefit-only pattern of automatic facilitation from the cost-benefit pattern of expectancy in higher order sequential effects. The data indicate that facilitation and expectancy are independent mechanisms that react in a different way to manipulations of response-stimulus interval, compatibility, and practice. It is suggested that facilitation effects are decaying memory traces related to the structural pathway of the reaction process, whereas expectancy effects are functional and only intervening in the information flow when enough time is available. © 1985 American Psychological Association.SCOPUS: ar.j