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Sunday, January 23, 2011

INFORMATION-PROCESSING METAPHOR

INFORMATION-PROCESSING METAPHOR
In the 1960s subdivisions of memory based upon informationprocessing models became popular. Following postwar developments in information technology, there had been a substantial growth in understanding the requirements of information storage during computer processing. A three-stage model of memory processing developed, reaching its fullest elaboration in the version proposed by Atkinson and Shiffrin (1968). In these stage models, information was considered to be first held very briefly in sensory memories before a selection of this information was transferred to a short-term store. From here, a yet smaller amount made its way into a long-term memory store.

Sensory memories
Evidence for sensory memory stores came from experiments such as Sperling’s (1960). He presented displays of 12 letters very briefly (e.g. 50 ms) to participants. Although they could report only about four letters, Sperling suspected that they might actually be able to remember more letters, but they could not hold them in mind long enough to report them. To test this hypothesis, Sperling briefly presented the letters as a matrix containing three rows, and then sounded a tone. Participants had been instructed to report only part of the array – which part depended on the pitch of the tone. Using this partial report procedure, Sperling found that people could recall about three letters from any row of four, which meant that they could actually potentially recall (for just a very brief period) about nine out of the twelve letters. Psychologists inferred from research such as this that there is a sensory memory store which holds a large amount of incoming perceptual information very briefly while selected elemens are processed. This sensory memory for visual information was termed iconic memory by Neisser (1967). Sensory memory for auditory information was referred to as echoic memory. Sensory memories are generally characterized as being rich in content, but very brief in duration.


Short- and long-term memories
Beyond the sensory memories, the information-processing models hypothesized one or more short-term stores that held information for a few seconds. The verbal short-term store has received the most research attention, its existence being inferred in part from the recency effect in free recall. For example, Postman and Phillips (1965) asked their participants to free recall lists of 10, 20 or 30 words. With immediate recall, the participants tended to be much better at recalling the last few words that had been presented than words from the middle of the list. But this recency effect disappeared if testing was delayed by as little as 15 seconds, so long as the delay involved verbal activity by the participant. The interpretation of the recency effect was that the last few items were being retrieved from a short-term store of rather limited capacity. The short-term store was believed to retain information primarily in an acoustic or phonological form (Baddeley, 1966) – a view that received additional support fro the errors that appear during short-term retention, even when the material to be retained is presented visually. Conrad and Hull (1964), for example, showed that visually presented sequences of letters that are similar in sound (e.g. P, D, B, V, C, T) were harder to recall correctly than were sequences of dissimilar-sounding letters (e.g. W, K, L, Y, R, Z).

On the other hand, long-term memory was believed to be stored primarily in terms of the meaning of the information. So, when asked to remember meaningful sentences, people usually cannot reproduce the exact wording, but they can generally report the meaning of what has been encountered (e.g. Sachs, 1967).

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