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. 598This document is copyrighted by the American Psychological Association or one of its allied publishers.This article is intended solely for the personal use of the individual user and is not to be disseminated broadly.

Two experiments examined the speed-accuracy tradeoff for stimuli used by Martin (1979), some of which have a Stroop-like conflict between the relevant (to-be-judged) and the irrelevant aspect. Speed of transmitting information about a local aspect was significantly reduced when the irrelevant global aspect conflicted with the relevant local aspect, while speed of transmitting information about the global aspect was not affected when the irrelevant local aspect conflicted with the relevant global aspect. This result, when extrapolated to the accuracy level of an ordinary reaction-time task, fitted very well the reaction-time predictions of the global precedence model proposed by Navon (1977). However, other results were incongruent with the fundamental assumption of that model: that global features are accumulated with temporal priority over local features. The finding that, independently of speed, information transmission of the global aspect started later when the irrelevant local aspect was conflicting, corroborates Miller's (1981a) conclusion that global and local features are available with a similar time course. Global precedence is therefore a postperceptual effect; absence of interaction with 8-R compatibility suggested that it operated before the response selection stage. The term global dominance may be preferred, because it avoids the implication of prior availability for the global aspect. Furthermore, the possibility of whether Stroop conflict should be considered a necessary condition for global dominance is discussed.This article is concerned with the accumulation of information of a visual form and, in particular, with whether transmission of global information precedes transmission of local (detail) information. For the purpose of this paper, we conceive of perception as a process of gradual feature accumulation. Furthermore, in line with the continuous-flow model of Eriksen and Schultz (1978, 1979), we assume that a subject's response is based upon the amount of information accumulated at that particular instant. The ontogenesis of the percept ("Aktualgenese" in terms of the Leipzig School of Gestalt Psychology) will therefore be reflected by the response of the moment.For the global-to-local hypothesis, the distinction between global and local features is a basic one. As opposed to feature models in which global features are composites of local features (Gibson, 1969;Selfridge, 1959;Treisman & Gelade, 1980), the globalto-local hypothesis states that perception begins with a global whole to which local details are gradually added. According to the global precedence model, global and local features denote separate sets of features. Thus, global feature availability is not depen-

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