Atkinson-Shiffrin theory
From Freepedia
Atkinson-Shiffrin theory is a psychological theory proposed in 1971. It was the first model to suggest that memory involves a sequence of three stages:
- Sensory memory
- Working or short-term memory
- Long-term memory
Summary
Sensory memory (also called the sensory register) involves two components:
- iconic memory: the storage of visual information, lasting about half a second
- echoic memory: the storage of auditory information, lasting up to two seconds
Information from the environment is filtered through this sensory register and passed on to the short-term memory circuit. Short-term memory can only hold information for about 30 seconds, and is limited to about seven units of information. In contrast, sensory memory seems to include all visual and auditory information that is perceived, so very little of this is apparently passed on to the short-term memory system. The short-term memory storage system has a rehearsal feature, organizational processes like chunking, and retrieval processes that affect which information is passed on to the long-term memory system.
In this model, long-term memory refers to anything that lasts beyond the 30 second lifespan of short-term memory, which accumulates to an enormous volume over time. It is divided into subsets based on the organizational principles set forth by the short-term memory system.
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. Atkinson and Shiffrin used this as evidence that the words at the end were still being held in the sensory memory.
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.
