Long-term Memory - Dual-store Memory Model

Dual-store Memory Model

According to Miller, whose paper in 1956 popularized the theory of the “magic number seven”, short-term memory is limited to a certain number of chunks of information, while long-term memory has a limitless store.

According to the Atkinson-Shiffrin memory model, a dual-store memory model set forth by Atkinson and Shiffrin in 1968, memories can reside in the short-term “buffer” for a limited time while they are simultaneously strengthening their associations in long-term memory. When items are first presented, they enter short-term memory, but because it has limited space, as new items enter, old ones leave. However, each time an item is rehearsed while it is in short-term memory, it is also increasing its strength in long-term memory. The longer an item stays in short-term memory, the stronger the association becomes in long-term memory. In long-term store, items are recalled through retrieval cues in a two-step process. First, context is used as a cue to probabilistically select an item to be potentially recalled. Second, that item is probabilistically determined to be recalled or not.

The transfer of items from short-term to long-term memory is called consolidation. Theories on consolidation are supported by concussion studies. The claim is that concussions completely knock out the working memory as well as the consolidation process, which is critical because if something interrupts this process the subject will have a very poor memory of what happened prior. One study has confirmed this theory.

In 1974 Baddeley and Hitch proposed an alternative theory to the Atkinson-Shiffrin memory model: Baddeley's model of working memory. According to this theory, short-term memory is divided into different slave systems for different types of input items, and there is an executive control supervising what items enter and exit those systems. The slave systems include the phonological loop, the visuo-spatial sketchpad, and later Baddeley added the episodic buffer.

Biologically, short-term memory is a temporary potentiation of neural connections that can become long-term memory through the process of rehearsal and meaningful association. Not much is known about the underlying biological mechanisms of long-term memory, but the process of long-term potentiation, which involves a physical change in the structure of neurons, has been proposed as the mechanism by which short-term memories move into long-term storage. The time scale involved at each level of memory processing remains under investigation.

As long-term memory is subject to fading in the natural forgetting process, several recalls/retrievals of memory may be needed for long-term memories to last for years, dependent also on the depth of processing. Individual retrievals can take place in increasing intervals in accordance with the principle of spaced repetition. This can happen quite naturally through reflection or deliberate recall (also known as recapitulation), often dependent on the perceived importance of the material.