Chapter Summary

• Introduction. The information stored in long-term memory is used in several ways. Various theories have been put forward to categorise long-term memory, and to explain how it works. These theories have recently become more similar to each other. Research on amnesic patients has been of value in testing existing theories of long-term memory, and in suggesting theoretical developments.

• Episodic and semantic memory. Episodic memory possesses a sense of conscious recollection of the past that is lacking in semantic memory. However, the way in which information is registered in episodic and semantic memory is very similar, and the encoding specificity principles applies to both types of memory. Episodic memory involves the prefrontal cortex to a greater extent than does semantic memory. The left prefrontal cortex is more active during episodic encoding, whereas the right prefrontal cortex is more active during episodic memory retrieval.

• Implicit memory. Implicit memory differs from explicit memory in that there is an absence of conscious recollection. The relative contributions of implicit and explicit memory can be assessed by comparing performance on inclusion and exclusion tests. There is an important distinction between perceptual priming and conceptual priming. Perceptual priming is influenced more by manipulation of study modality than level of processing, whereas the opposite is the case for conceptual priming. There are probably several kinds of implicit memory, and the term "implicit memory" is often used in a descriptive way.

• Implicit learning. Implicit learning occurs when there is a partial or total inability to verbalis what has been learned. In order to show that there is little or no conscious awareness of what hae been learned, it is necessary for participants to be asked to provide the information that is actually responsible for improved performance, and the test of awareness must be sensitive to all of the relevant knowledge.

• Transfer appropriate processing. According to Roediger, there is an important distinction between data-driven or perceptual processes and conceptually driven processes. Memory performance will be better when there is a match between the processes used at study and at test Various criteria have been proposed to decide whether a memory test involves mainly perceptual. or conceptual processes. The distinction between perceptual and conceptual processes is oversimplified, and Roediger's theory cannot account fully for the findings from amnesic patients.

• Amnesia. The study of amnesia has led to new theoretical developments, and has provided a test-bed for existing theories. The amnesic syndrome consists of retrograde amnesia, anterograde amnesia, intact short-term memory, normal intelligence, and residual learning ability. It can be produced by damage to the diencephalon or to the medial temporal lobe. There is usually a temporal gradient with retrograde amnesia, and the extent of retrograde amnesia does not correlate highly with that of anterograde amnesia. Residual learning ability in amnesics typically extends to sensori-motor and perceptual skills, repetition priming (perceptual and conceptual), and some forms of conditioning. • Theories of amnesia. Amnesic patients often have worse episodic memory than semantic memory. However, they generally have great difficulty in forming new semantic memories even though semantic memories formed before the onset of amnesia are largely intact. There is evidence that amnesic patients have a deficit in contextual processing. However, it is not clear why amnesic patients have particular problems with contextual information. In addition, the context processing deficit theory does not explain amnesics' poor recognition-memory performance. Amnesics generally show impaired explicit memory but essentially intact implicit memory. However, the explicit/implicit distinction describes rather than explains amnesia, and amnesics have impaired performance on some forms of repetition priming that depend on implicit memory.

According to Roediger, amnesic patients have fairly intact data-driven or perceptual processing but impaired conceptual processing, and conceptual processing is generally required on tests of explicit memory. However, amnesics perform poorly on explicit memory tests even when the tests require perceptual or data-driven processes. There is support for the notion that amnesic patients have an intact procedural learning system but an impaired declarative learning system (including episodic and semantic memory). The declarative memory system is based on the hippocampus and anatomically related structures in the medial temporal lobes and the diencephalon. Amnesics find it hard to store integrated or linked information in long-term memory.

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