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Short-Term Memory

Short-term memory (STM) refers to what a person can remember from the immediate past. This is conceptually distinct from what a person can remember from all information stored during a lifetime, called long-term memory (LTM). There have been debates among memory researchers as to whether STM is a different memory store from LTM or whether STM is merely the information that is held in an active state within LTM. Regardless of how STM is conceptualized, in practical terms, it is one link in a much bigger chain of processes that begins with attention and perception and can lead to higher order cognition and learning.

This entry describes the modal model of memory, a model that helped define STM and was able to predict key features of STM such as its capacity and duration. It also describes challenges to the modal model, as well as a newer model that better explains the complex, real-world processes such as learning, multitasking, and intelligence.

The Modal Model of Memory

Building on the work of memory researchers in the 1950s and 1960s, Richard Atkinson and Richard Shiffrin, in 1968, proposed the multi-store model, which is the essence of the modal model. The theory was intended to account for how information from the outside world is encoded and gets into LTM. Visual or auditory information first goes into a sensory register (the first store), which acts as a perceptual buffer. Research by George Sperling in 1960 suggests that information can be held as physical features for about one quarter to one half of a second before it fades from sensory memory. Once stimulus information is categorized as known concepts by relying on LTM to identify its categorical features, the information is transferred to the second store, the short-term store. There the information is kept active in STM by rehearsal or repeating it over and over to oneself.

The longer an item is kept in STM and the more times it is rehearsed, the greater the chance it will be transferred to the third and final store, the long-term store. Some information will not be transferred to LTM due to longer times between opportunities to rehearse or more or lengthier items to rehearse. For example, in 1974, Alan Baddeley showed that the slower a person speaks, and therefore the longer the space between words, the greater the chance that the information will not transfer to LTM. Whether one can later retrieve the information depends on how much it is rehearsed or elaborated upon and the quality of the retrieval cues. In summary, according to the modal model, an individual must pay attention to stimuli in order to encode it; the individual must rehearse items in STM in order for them to transfer to LTM.

Measuring STM’s Capacity

Capacity of STM is often measured by the digit span test, in which an increasing span of digits (starting with four digits) is read quickly and then recalled from memory in order of presentation. Typical recall is 5 or 6 items, and recall above 7 is unusual. A useful psychological process to aid STM is called chunking, described by George Miller and Herbert Simon. They demonstrated that if information is chunked into high-level, meaningful units, then much more information might be recalled. For example, B I C I A F might be challenging to recall in order, but FBI CIA would not be. Yet those two letter strings are almost identical except for the transposition of one letter from the back to the front.

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