ABSTRACT
How is complex sequential material acquired, processed, and represented when there is no intention to learn? Recent research (Lewicki, Hill, & Bizot, 1988) has demonstrated that subjects placed in a choice reaction time task progressively become sensitive to the sequential structure of the stimulus material despite their unawareness of its existence. This paper aims to provide a detailed informationprocessing model of this phenomenon in an experimental situation involving complex and probabilistic temporal contingencies. We report on two experiments exploring a six-choice serial reaction time task. Unbeknownst to subjects, successive stimuli followed a sequence derived from "noisy" finite-state grammars. After considerable practice (60,000 exposures), subjects acquired a body of procedural knowledge about the sequential structure of the material, although they were unaware of the manipulation, and displayed little or no verbalizable knowledge about it. Experiment 2 attempted to identify limits on subjects' ability to encode the temporal context by using more distant contingencies that spanned irrelevant material. Taken together, the results indicate that subjects become progressively more sensitive to the temporal context set by previous elements of the sequence, up to three elements. Responses are also affected by carry-over effects from recent trials. A PDP model that incorporates sensitivity to the
46 CLEEREMANS AND McCLELLAND
INTRODUCTION
In many situations, learning does not proceed in the explicit and goal-directed way characteristic of traditional models of cognition (Newell & Simon, 1972). Rather, it appears that a good deal of our knowledge and skills are acquired in an incidental and unintentional manner. The evidence supporting this claim is overwhelming: In his recent review article, Reber (1989) analyzed as many as about 40 detailed empirical studies that document the existence of implicit learning. At least three different paradigms have yielded robust results indicating that learning does not necessarily entail awareness of the resulting knowledge or of the learning experience itself: artificial language learning (Dulany, Carlson, & Dewey, 1984; Reber, 1967, 1989; Servan-Schreiber & Anderson, 1990), system control (Berry & Broadbent, 1984; Hayes & Broadbent, 1988), and sequential pattern acquisition (Cohen, lvry, & Keele, 1990; Lewicki, Czyzewska, & Hoffman, 1987; Lewicki et al., 1988; Nissen & Bullemer, 1987; Willingham, Nissen, & Bullemer, 1989). The classic result in these experimental situations is that "subjects are able to acquire specific procedural knowledge (i.e., processing rules) not only without being able to articulate what they have learned, but even without being aware that they had learned anything" (Lewicki et al., 1987, p. 523). Related research with neurologically impaired patients (see Schacter, 1987, for a review) also provides strong evidence for the existence of a functional dissociation between explicit memory (conscious recollection) and implicit memory (a facilitation of performance without conscious recollection).
