In three experiments, we studied the relation between degree of implicit learning and two aspects of short-term memory: (1) the activation level of the to-be-learned information, and (2)individual differences in short-term memory capacity. In all the experiments, we used the Nissen and Bullemer (1987) serial reaction time paradigm or a modification thereof. The effects of activation level were assessed by experimentally manipulating the rate of presentation. Individual differences in short-term memory capacity were assessed via traditional span measures. The experiments demonstrated that the rate of presentation reliably affected an indirect measure of learning (i.e., response time) under both incidental and intentional task instructions and under both single-task and dual-task conditions. Short-term memory span was reliably related to the indirect measure of learning only in some experimental conditions. The findings represent important constraints for models of implicit serial learning and are discussed within a general framework for understanding implicit learning and memory.Serial learning is typically governed by the explicit intention to learn, as is perhaps most obvious in children's attempts to acquire the algorithms underlying mental arithmetic. Nevertheless, it appears that a good deal of serial learning is incidental and unintentional. For example, although most adults have learned to recognize and produce syntactically correct sentences, very few are, in fact, able to state the underlying rules of grammar. The purpose of the present article is twofold: (1) to describe a general framework for understanding implicit learning, and (2) to empirically test two of the predictions generated by the framework. The focus of our work is on implicit serial learning I-that is, the acquisition of serial information in the absence of explicit knowledge about the acquired information (see, e.g., Lewicki, Czyzewska, & Hoffman, 1987).We examine implicit serial learning by using a task originally introduced by Nissen and Bullemer (1987; see 95also Cohen, Ivry, & Keele, 1990;Knopman, 1991;Nissen, Knopman, & Schacter, 1987;Nissen, Willingham, & Hartman, 1989;Stadler, 1989Stadler, , 1992Willingham, Nissen, & Bullemer, 1989). In the Nissen and Bullemer task, an asterisk is presented at one of four different spatial locations that are arranged in a horizontal line on a computer screen. Each of the locations is mapped onto a different response key. The subjects' task is to press the key that corresponds to the asterisk's screen location. The asterisks are presented one at a time, and they follow either a repeating sequence or a random sequence of screen locations. Recent experiments with the Nissen and Bullemer task have primarily addressed three theoretical issues concerning explicit and implicit learning: (1) the independence of the implicit and explicit learning modes, (2) the role of attention in implicit learning, and (3) the nature of the learning mechanism(s) underlying implicit learning. Independence of Learning...

Two experiments tested H. Haider and P. A. Frensch's (1996) information-reduction hypothesis that people learn, with practice, to distinguish between task-relevant and task-redundant information and to limit their processing to task-relevant information. Participants verified alphabetic strings (e.g., "E [4] J K L") containing task-relevant and task-redundant information. In Experiment 1, the positioning of task-relevant information within the strings and the consistency of positioning were manipulated. Degree of information reduction as reflected in reduced reaction times was not affected by the positioning of the relevant information and was only slightly affected by consistency of the positioning. In Experiment 2, eye movements were recorded. Results suggest that task-redundant information is ignored at a perceptual rather than a conceptual level of processing. Thus, existing theories of skill acquisition should include mechanisms that capture the practice-related increase in the selective use of information.

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Thirty-six younger adults (10 male, 26 female; ages 18 to 38 years) and 36 older adults (14 male, 22 female; ages 61 to 80 years) completed simple and complex paper-and-pencil subtraction tests and solved a series of simple and complex computer-presented subtraction problems. For the computer task, strategies and solution times were recorded on a trial-by-trial basis. Older Ss used a developmentally more mature mix of problem-solving strategies to solve both simple and complex subtraction problems. Analyses of component scores derived from the solution times suggest that the older Ss are slower at number encoding and number production but faster at executing the borrow procedure. In contrast, groups did not appear to differ in the speed of subtraction fact retrieval. Results from a computational simulation are consistent with the interpretation that older adults' advantage for strategy choices and for the speed of executing the borrow procedure might result from more practice solving subtraction problems.

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