Atkinson-Shiffrin theory

Atkinson-Shiffrin theory is a psychological theory proposed in 1968. It proposed that human memory involves a sequence of three stages:


 * 1) Sensory memory
 * 2) Working memory or short-term memory
 * 3) Long-term memory

Summary
The multi-store model of memory is an explanation of how memory processes work. You hear and see and feel many things, but only a small number are remembered. The model was first described by Atkinson and Shiffrin in 1968.

Sensory memory The sense organs have a limited ability to store information about the world in a fairly unprocessed way for less than a second. The visual system possesses iconic memory for visual stimuli such as shape, size, colour and location (but not meaning), whereas the hearing system has echoic memory for auditory stimuli. Coltheart et al (1974) have argued that the momentary freezing of visual input allows us to select which aspects of the input should go on for further memory processing. The existence of sensory memory has been experimentally demonstrated by Sperling (1960) using a tachistoscope.

Short-term memory Information selected by attention from sensory memory, may pass into short term memory (STM). This allows us to retain information long enough to use it, e.g. looking up a telephone number and remembering it long enough to dial it. Peterson and Peterson (1959) have demonstrated that STM last approximately between 15 and 30 seconds, unless people rehearse the material, while Miller (1956) has found that STM has a limited capacity of around 7 ‘chunks’ of information. STM also appears to mostly encode memory acoustically (in terms of sound) as Conrad (1964) has demonstrated, but can also retain visuospatial images.

Long-term memory LTM provides the lasting retention of information and skills, from minutes to a lifetime. Long term memory appears to have an almost limitless capacity to retain information, but it could never be measured as it would take too long. LT information seems to be encoded mainly in terms of meaning (semantic memory) as Baddeley has shown, but also retains procedural skills and imagery.

Evidence
In a type of memory test called a free recall task, subjects memorize a list of words and then repeat them. When they are allowed to repeat the words immediately after memorizing them, subjects recall the last few words in the list much better than words in the middle. But if subjects are delayed before they are given a chance to repeat the words, this effect disappears. This effect is called the recency effect. Atkinson and Shiffrin used this as evidence that the words at the end were still being held in the sensory memory.

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In another version of the free recall task, subjects were given a list of words that sounded similar (like cat, map, man, mat). On these tests, subjects performed very poorly. When they were given lists of words that sounded unrelated, but had similar meanings, their immediate recall was normal. But when asked to recall the similar words after a delay, suddenly they performed much better than they did after delays when the words were unrelated. Atkinson and Shiffrin believed this to show that short term memory uses acoustic information, but long term memory encodes things based on their meaning.

Amnesics with impaired long-term memory systems have been given similar tasks. They tend to perform just as well as healthy control subjects, which led Atkinson and Shiffrin to believe this was still more evidence for separate short-term and long-term memory systems.

Later Developments
This model provided an important framework for learning and memory theories to evolve from, but a number of problems with it have been cited since. Since each element in the model builds off the one preceding, it cannot explain the rare situations where short-term memory is impaired, but long-term memory is not. According to this model, information that can't make it through short-term memory has no way to become encoded in long-term memory.

Atkinson and Shiffrin also refrain from proposing any mechanisms or processes that might be responsible for encoding memories and transferring them between the three systems. The model is a hypothetical layout of the function of memory systems, but not in any way representative of a physical "map" of memory systems.

Many newer models have been created that can better account for these other characteristics, and a tremendous body of research on the physical layout of memory systems has emerged. As the oldest and simplest model, this is often the model used in introductory courses, but can no longer be considered entirely accurate or comprehensive.

The rehearsal loop also must be included in the transfer of memory into LTM from the STM, it is said that for things to be transferred correctly they must negate the rehearsal loop to ensure full remembrance.