Proceedings of the Annual Meeting of the Cognitive Science Society

How is complex sequential material acquired, processed, and represented wlien 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 information-processing model of this phenomenon in an experimental situation involving complex and probabilistic temporal contingencies. We report on two experiments exploring a 6-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 carryover effects from recent trials. A PDP model that incorporates sensitivity to the sequential structure and carry-over effects is shown to capture key