Cognitive Skill Learning

Investigation of practice-related changes in the verbgeneration task provides a convenient segue into a discussion of skill acquisition—another vital aspect of memory. After 15 min of practice on the verbgeneration task, 90% of the verbs that participants generated were rote responses that had been consistently associated with the nouns. Participants no longer had to search through memory for a novel association; instead, they could quickly recall a response they gave previously. Analysis of the difference between the PET images early and late in the verbgeneration task showed that, with practice, activity decreased in the anterior cingulate, left prefrontal cortex, bilateral inferior frontal gyri, left temporal cortex, and right cerebellum—the very areas that were active when verb generation was compared to word reading. In fact, after practice the PET images were indistinguishable from those of word reading. Increases in activation with practice were observed in the precuneus and cuneus on the medial wall of the posterior cerebrum and in the right superior parietal cortex. These shifts in activation could be due to decreased demand on attention and effort, decreased searching of semantic memory, or some other factor.

Without further evidence, it is hard to distinguish among these causes. Certainly evidence exists that some of these areas are involved in other cognitive processes. For example, the left prefrontal cortex is activated in verbal working memory tasks and in the encoding of long-term memories, as we reviewed earlier. The anterior cingulate is also activated in some overpracticed motor tasks, particularly when they might require attending, making inferences about a pattern, or anticipating future stimuli or feedback. One region that may have a clearer role in the practice effect seen in the verb-generation task is the insula, an area located anatomically near the region responsible for speech output and an area that showed increased activation in the verb-generation task with practice.

This activation may be an indication of increasing automaticity in producing verb associations given nouns as stimuli, a kind of stimulus-response connection that developed even over the course of relatively little practice.

Of course, one might ask whether skill in the verbgeneration task is a good example of cognitive skill learning in general. The shifts in activation in this task seem to result not from an improved ability to generate novel verbs, but rather from the ability to call up from memory the same verb the subject gave on the last trial, a kind of automatic stimulus-response mapping. It is not yet understood how true cognitive skills, such as the ability to make inferences and manipulate abstract concepts, are learned, except that their appearance in children seems to parallel development of the frontal lobes. However, a great deal of what we normally consider to be cognitive skills, such as expertise in chess, can be explained as the formation and retrieval of ever larger and more complex sets of associations in semantic memory.

A final example of cognitive skill learning comes from a PET study of categorization. Experimental studies have shown that people learn to categorize objects in several ways: through the application of rules, learning of specific exemplars of a category, and implicit learning of an average or "prototype" of the category. Patients with medial temporal damage, who have virtually no remaining episodic memory, fail on rule- and exemplar-based categorization but learn prototype-based categorization as readily as do normal participants. In the study, people classified pictures of contrived animals based on previous practice with similar (but not identical) animals. One practice group learned to categorize animals by a rule, and the other group learned the categories by trial and error. The rule group categorized the new animals presented during scanning by applying the rule. The trial-and-error group categorized animals during PET scanning on the basis of their similarity to the animals they saw during training, an exemplar-based strategy. Only rule-based categorization activated the bilateral parietal cortex, right prefrontal cortex, and bilateral supplementary cortex, possibly reflecting greater working memory demands, attention shifting, and retrieval and application of the rule. Exemplar-based categorization activated the left extrastriate cortex and left cerebellum. The extrastriate activation may reflect greater use of a perceptually based memory trace in the exemplar-based strategy, consistent with the involvement of extrastriate visual cortex in studies of implicit memory. This study suggests that different learning regimens may have a profoundly different effect on the brain circuitry recruited to the task, at least for a task requiring categorization processes.

Conquering Fear In The 21th Century

Conquering Fear In The 21th Century

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