Neuropsychology: From Theory to Practice by David Andrewes

Author:David Andrewes [Andrewes, David]
Language: eng
Format: azw3, pdf
Publisher: Taylor and Francis
Published: 2015-12-22T05:00:00+00:00

5.7Implicit Memory Systems

5.7.1Introduction

There is a distinction between consciously encoded and retrieved memories, referred to as explicit memories (declarative), and other memories that are used without conscious realisation, such as implicit memories (non-declarative memories; Graf and Schacter, 1985; Squire, 1987). Here ‘conscious’ refers to the knowledge that you are recalling a memory. Included under the rubric of explicit or declarative memory are episodic (memory for events), autobiographical memory and semantic memory (memory for facts). The terms ‘declarative’ and ‘non-declarative’ were introduced as an indication that these two types of memory were based on memory systems that were separable and served by distinct neural mechanisms. This remains mostly supported, but a classification of memories into conscious versus non-conscious has been questioned (see Henke, 2010) and this is given further discussion under ‘Further Topics’ later in this chapter. In this section the terms ‘explicit’ and ‘implicit’ memory will be used instead of ‘declarative’ versus ‘non-declarative’, since the former terms are more neuropsychologically neutral and make fewer assumptions concerning the brain areas associated with the two types of memory.

Implicit memories have at least three features that set them apart from explicit memories: (1) they do not require a conscious acknowledgement of learning; (2) they depend mainly on structures other than the extended memory system; and accordingly (3) they may be completed by patients with amnesia with a surprising degree of efficiency.

Explicit memory involves the acknowledgement of having learned the information previously, for example retrieving the context of learning, as in the case of recalling episodic or autobiographical memories. There are some forms of explicit memory such as semantic memory that sit rather uneasily within this categorisation, although it is interesting that we often are immediately conscious of whether or not we know a fact.

Sergei Korsakoff, who is discussed above, describes one of the earliest accounts of a patient with amnesia showing implicit memory. The patient spontaneously asked whether he would be shocked on that day (electro-convulsive therapy), without any ability to consciously remember the event of being shocked the day before (cited by Schacter, 1987). Another early demonstration of implicit memory was from the Swiss psychologist Édouard Claparède (1911) who describes a woman who had reasonable intellectual abilities but who had no ability to learn any new information. Édouard saw the patient on his rounds on a daily basis but the patient was unable to recognise him. The patient would on occasions shake him by the hand as a way of introduction. As an experiment, the psychologist placed a pin in his hand so that when the patient shook his hand on one ward round she felt a stabbing pain. Although unkind, it transpired on the next day that the experiment was not just a sadistic waste of time, for the patient refused to shake his hand. When asked why she refused she had no idea, for she was unable to remember the incident of the day before. Apparently there was just a sense of undefined foreboding.

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