MEMORY
Early research into memory led to a multi-store model consisting of: sensory memory, short-term memory and long-term memory. The flow of information between these different stores is often represented as controlled by a central executive.
Sensory memory is of extremely short duration, enabling the language user to retain a brief verbatim impression of the actual sound of speech (echoic memory) or the distribution of words on the page (iconic memory).
Short-term memory (STM) holds a limited number of items for current processing. They might be items extracted from an incoming signal or items retrieved from the permanent store of long-term memory. Current theories of STM view it not simply as a store but as actively engaged in cognitive operations; hence a preference for the term working memory.
Long-term memory (LTM) has unlimited capacity. It can be of extremely long duration, though the information it contains is reinforced by being used. LTM is said to contain knowledge of two types: declarative knowledge which gives us access to facts (knowledge that) and procedural knowledge which enables us to perform processes (knowledge how).
When subjects are asked to recall written or spoken lists of words, there is a primacy effect, with the first words on the list recalled better than those in the middle. This is associated with successful storage in LTM, subjects having had more opportunity to rehearse these earlier words in their minds. There is also a recency effect, with higher recall of the most recent words. This is attributed to subjects being able to retrieve words that are still available in STM. Patients suffering from a certain type of amnesia manifest the recency effect but not the primacy effect. This finding supports the theory that there are two separate components of memory, since it appears to reflect an inability to transfer words from one store (STM) to another (LTM).
However, other researchers have produced contradictory findings, and one body of opinion now favours a unitary memory store. In support of this view, there is evidence that the code in STM (the form in which information is stored) resembles more closely that of LTM than was originally supposed. An embedded processes model of memory suggests that STM as a whole is simply the currently activated part of LTM.
See also: Long-term memory, Sensory memory, Short-term memory, Working memory
Further reading: Baddeley (1982, 1997); Cohen (1989); Cohen et al. (1993); Henderson (1999)
