Academic journal article Memory & Cognition

Distinguishing the Contributions of Implicit and Explicit Processes to Performance of the Weather Prediction Task

Academic journal article Memory & Cognition

Distinguishing the Contributions of Implicit and Explicit Processes to Performance of the Weather Prediction Task

Article excerpt

Examinations of the cognitive neuroscience of category learning frequently rely on probabilistic classification-learning tasks-namely, the weather prediction task (WPT)-to study the neural mechanisms of implicit learning. Accumulating evidence suggests that the task also depends on explicit-learning processes. The present investigation manipulated the WPT to assess the specific contributions of implicit- and explicit-learning processes to performance, with a particular focus on how the contributions of these processes change as the task progresses. In Experiment 1, a manipulation designed to disrupt implicit-learning processes had no effect on classification accuracy or the distribution of individual response strategies. In Experiment 2, by contrast, a manipulation designed to disrupt explicit-learning processes substantially reduced classification accuracy and reduced the number of participants who relied on a correct response strategy. The present findings suggest that WPT learning is not an effective tool for investigating nondeclarative learning processes.

Responding to environmental events often demands rapid categorization of both familiar and novel stimuli. The learning required for such categorization readily occurs under a variety of circumstances, and it is generally believed that such learning is supported by multiple memory systems (Ashby, Alfonso-Reese, Turken, & Waldron, 1998; Ashby & Valentin, 2005; Maddox & Ashby, 2004; Poldrack et al., 2001; Poldrack & Packard, 2003; Smith, Patalano, & Jonides, 1998; but see Lagnado, Newell, Kahan, & Shanks, 2006, and Nosofsky & Johansen, 2000, for discussions of a unitary system of categorization). At least one of these systems supports declarative, explicit category learning,1 which requires active memorization and/or hypothesis testing, whereas at least one other system supports nondeclarative, implicit category learning, which develops in a gradual and nonconscious manner.

A number of cognitive, neuropsychological, and neuroimaging studies have supported the existence of multiple category-learning systems (for relevant reviews, see Ashby & Valentin, 2005; Shohamy, Myers, Kalanithi, & Gluck, 2008). In these investigations, one of the most commonly used paradigms is the weather prediction task (WPT), a probabilistic classification task designed to assess gradual, incremental learning over many trials (Knowlton, Squire, & Gluck, 1994). On this task, participants must categorize a set of visually presented cues that are probabilistically related to one of two outcomes and then receive feedback on the accuracy of their response. The probabilistic cue-outcome relationships are thought to disrupt declarative-learning processes (Knowlton, Mangels, & Squire, 1996; Knowlton et al., 1994; Poldrack et al., 2001). For this reason, the WPT has been used extensively to examine the neural mechanisms that support nondeclarative learning (Aron, Gluck, & Poldrack, 2005; Foerde, Knowlton, & Poldrack, 2006; Poldrack et al., 2001; Poldrack, Prabakharan, Seger, & Gabrieli, 1999; Shohamy et al., 2004) and to assess the integrity of nondeclarative learning in various neuropsychological populations (Beninger et al., 2003; Eldridge, Masterman, & Knowlton, 2002; Foerde et al., 2008; Hopkins, Myers, Shohamy, Grossman, & Gluck, 2004; Kéri, Szlobodnyik, Benedek, Janka, & Gádoros, 2002; Knowlton et al., 1996; Knowlton et al., 1994).

Although the WPT is commonly considered a measure of nondeclarative learning, neuropsychological evidence suggests that the task may rely on declarative-learning processes. Patients with focal damage of the medial temporal lobe (MTL), who experience a selective deficit of declarative memory, exhibit minimal learning even with considerable practice (Hopkins et al., 2004; Meeter, Myers, Shohamy, Hopkins, & Gluck, 2006). Furthermore, neuropsychological research with healthy older adults and patients with Parkinson's disease indicates that WPT learning is greater among those with higher levels of executive function (Knowlton et al. …

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