Memory

Perceptual activity leaves traces in memory, freeing behavior from dominance by stimuli in the immediate present. The knowledge stored in memory consists of two broad forms: declarative knowledge, which can be either true or false, and procedural knowledge of how certain goals are to be accomplished. Procedural knowledge can be further classified into cognitive and motor skills, such as one's knowledge of arithmetic or grammar, how to tie one's shoes, or how to drive a standard-shift car. Similarly, declarative knowledge can be subdivided into episodic memories of specific experiences that occurred at a particular point in space and time, such as one's memory of eating sushi for dinner at home last Thursday, and semantic memories that are more generic in nature, such as one's knowledge that sushi is a Japanese dish made of rice, vegetables, and fish. In theory, many semantic memories are formed by abstraction from related episodic memories, and much procedural knowledge represents a transformation of declarative knowledge.

Most research on memory has focused on episodic memories for specific events and is based on an analysis of memory into three stages of encoding, storage, and retrieval. Early views of memory that made a structural distinction between short- and long-term stores have now been replaced by a unitary view in which "short-term" (or "working") memory refers to those items that are actively engaged in processing at any moment. Earlier views of forgetting as a product of the loss of memories from storage have been replaced by the view that retention is a function of the extent of processing received by an item at the time of encoding and the amount of cue information available at the time of retrieval. The relations between encoding and retrieval processes are effectively captured by a general principle of encoding specificity (also known as transfer-appropriate processing), which states that the likelihood that an event will be remembered depends on the match between the information processed at the time of encoding and the information available at the time of retrieval.

Most research on memory has employed experimental tasks requiring conscious recollection, or the ability of subjects to recall or recognize past events. However, episodic memory may also be expressed implicitly in tasks that do not require conscious recollection in any form. For example, a subject who has recently read the word "veneer" will be more likely to complete the stem "ven" with this word than with the more common word "vendor." A great deal of experimental research shows that such priming effects can occur regardless of whether the study word is consciously remembered; in fact, they can occur in amnesic patients who have forgotten the study session in its entirety. Similarly, amnesic patients can learn new concepts without remembering any of the instances they have encountered, and they can acquire new cognitive and motor skills while failing to remember the learning trials. Along with the concept of automaticity, the dissociations observed between explicit and implicit expressions of memory have given new life to the notion of the psychological unconscious.

The dissociations observed between explicit and implicit expressions of episodic memory, between semantic and episodic memories, and between procedural and declarative knowledge are subject to a variety of interpretations. According to the multiple systems view, explicit (conscious) and implicit (unconscious) memories are served by different memory systems in the brain. The multiple systems view, in turn, is compatible with the neuroscientific view of the brain as a collection of modules, each specialized for a particular information-processing task. In contrast, researchers who prefer a processing view, while accepting that there is some degree of specialization in the brain, explain these same dissociations as generated by different processes that operate in the context of a single memory system. For example, according to one processing view, implicit memories are the product of automatic, attention-free processes, whereas explicit memories are the product of effortful, attention-demanding ones. In general, processing views are compatible with computational theories of memory, which typically assume that different memory tasks require the processing of different features of memories stored in a single memory system. One of the interesting features of the debate over explicit and implicit memory is how little contact there has been between neuroscientific and computational views of memory.

Conquering Fear In The 21th Century

Conquering Fear In The 21th Century

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