Control of Response Initiation:
Mechanisms of Adaptation to Recent Experience

Michael C. Mozer, Sachiko Kinoshita, and Colin Davis

In most cognitive and motor tasks, speed-accuracy trade offs are observed: Individuals can respond slowly and accurately, or quickly yet be prone to errors. What sort of control mechanism governs the initiation of a behavioral response? A strong source of constraint on a theory of control comes from the finding that response time and accuracy depend on the recent stimulus environment: when stimuli can be characterize on an easy-hard dimension (e.g., word frequency in a naming task), an easy item is responded to more slowly when intermixed with hard items than when presented among other easy items; likewise, hard items are responded to more quickly when intermixed with easy items. We propose a computational theory with three components: a model of temporal dynamics of information processing, a decision criterion specifying when a response should be initiated, and a mechanism of adaptation to the stimulus environment. Performance during the course of an experimental trial is cast in terms of a utility function that increases with accuracy and decreases with response time. We assume a decision criterion that initiates a response at the point in time that maximizes expected utility. We posit that the blocking effect arises because information concerning recent trial difficulty is incorporated into the utility estimate. We present further behavioral studies to validate predictions of the theory.

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