The Varieties of Conscious and Unconscious Memory Systems

Although there may be innumerable different memory systems in the brain, many cognitive scientists have followed the lead of the psychologist Endel Tulving (1972), who differentiated experiential memory, which he called episodic, from what he termed semantic memory. Episodic memory is temporally dated, whereas semantic memory is not. Semantic memory refers to knowledge-based memory, the memory of acquired information not in any sense autobiographical.

Another well-known category of memory is that of procedural memory, the memory of motor routines, such as learning to ride a bicycle or learning to play the piano. Unlike episodic memory, which can potentially become conscious, implicit procedural memory is incapable of becoming conscious. That is to say, we cannot consciously recall (without performing the action) the sequence of motor acts required to ride a bicycle or tie our shoelaces. Procedural memory is without meaning and has no relation to metaphor.

Some cognitive scientists and neurobiologists mistakenly believe that implicit or procedural memory is the only form of unconscious memory, I would judge this opinion to be a profound misunderstanding. This is a significant point of disagreement between psychoanalysis and neuroscience re garding the nature of the unconscious. Psychoanalysts believe unquestionably that the unconscious is a source of potential meaning—that the unconscious does not consist only of the memory of motor routines. What Tulving calls episodic (autobiographical) memory is also unconscious, especially the memory of unassimilated experiences. Unlike procedural memory, episodic memory, the memory of the history of the self, is always potentially meaningful.

To limit the unconscious to the memory of motor routines is totally at odds with the hypothesis of an unconscious met-aphoric process that assumes unconscious memory to be potentially meaningful. As we shall see, this is a very important issue, for it is based on certain philosophical assumptions concerning the definition of mind. (I discuss this issue further in chapter 11.) There are many in the cognitive-science community who would limit the definition of mind to conscious experience and who believe that only procedural memory is implicit or unconscious. As procedural memory is devoid of semantic content, this view of human psychology is reminiscent of a discredited behaviorism that achieved a certain clarity by eliminating the mind.

What follows is Tulving's description of the distinction between episodic and semantic memory:

Episodic memory receives and stores information about temporally dated episodes or events, and temporal-spatial relations among these events. A perceptual event can be stored in the episodic system solely in terms of its perceptible properties or attributes, and it is always stored in terms of its autobiographical references to the already existing contents of the episodic memory store.

Semantic memory is the memory necessary for the use of language. It is a mental thesaurus of organized knowledge a person possesses about words and other verbal symbols, their meaning and referents, about relations among them, and about roles, formulas and algorithms for the manipulation of the symbols, concepts and relations. Semantic memory does not register perceptual properties of inputs, but rather cognitive referents to input signals. The semantic system permits the retrieval of information that was not directly stored in it, and retrieval of information leaves its contents unchanged. (1972, p. 385)

Tulving's statement that retrieval from the semantic (knowledge-based) memory systems leaves its contents unchanged, that semantic memory is not recontextualized, is an important characteristic that differentiates semantic from episodic (autobiographical) memory. Episodic memory is the memory of the self, and apart from trauma, the memory of the self is continually updated.

Neuroscientists have obtained evidence of neural correlates that confirm Tulving's categories of episodic and semantic memory. Children who sustained bilateral damage to their hippocampus developed amnesia for autobiographical (episodic) memory, while preserving the memory of acquired knowledge (semantic memory) (Vargha-Khadem, Gadian, et al. 1997). These researchers infer from their investigation that semantic memory is preserved when the underlying cerebral cortices are intact. This work also reinforces the belief that the hippocampus processes experiential (episodic) memory (Pally 1997). Tulving's distinction between episodic and semantic memory is also confirmed by laboratory experiments, as detailed by Daniel Schacter (1996).

0 0

Post a comment