Short-term memory: Standard model

The central part of the multi-store model Opens in new window was the short-term store. More recently, several theorists (e.g., Shiffrin, 1999) have proposed a revised theoretical account of it, called the standard model (Nairne, 2002a).

The main assumptions of the standard model are as follows:

• Information in short-term storage is in a state of activation.
• “Permanent knowledge is activated, as a byproduct of on-line cognitive processing, and comes to reside ‘in’ short-term memory. Short-term memory … is simply defined as the collective set of this activated information in memory” (Nairne, 2002a, p. 54).
• Currently activated information can be accessed immediately and effortlessly.
• “Activation is assumed to be fragile, and it can be quickly lost — through the operation of decay—in the absence of rehearsal” (Nairne, 2002a, p. 54).

In sum, the standard model is very simple:

Evidence

According to the standard model, short-term memory Opens in new window should be better for words that can be rehearsed rapidly than for words that take longer to rehearse: rapid rehearsal maintains activation thereby prevents decay.

Some evidence supports this prediction (e.g., Baddeley, Thompson, & Buchanan, 1975), but other evidence does not. For example, Lovatt, Avons, and Masterton (2000) used two-syllable words varying in their spoken duration.

According to the standard model, forgetting Opens in new window from short-term memory is due to decay. However, proactive interference Opens in new window (disruption of current learning and memory by previous learning) also plays an important role in forgetting from short term memory.

For example, Keppel and Underwood (1962) used the same task as Peterson and Peterson (1959). There was no forgetting over time on the very first trial, after which forgetting resembled that observed by Peterson and Peterson (1959). Why was this?

If forgetting from short-term memory is due to decay, then there should be rapid forgetting in the absence of rehearsal. That is precisely what was observed by Peterson and Peterson (1959).

However, Nairne, Whiteman, and Kelley (1999) argued that rapid forgetting is not inevitable. They presented their participants with five-item word lists, and took two steps to reduce the forgetting rate.

• First, memory was tested only for order information and not for the words themselves. This was done by re-presenting the five words at test, and asking participants to arrange them in order.
• Second, the words on each trial differed, to reduce proactive interference. There was a rehearsal-prevention task during the retention interval (reading aloud digits presented on a screen). There was remarkably little forgetting even over 96 seconds , thus providing little support for the notion that decay causes forgetting in short-term memory.

There is evidence against the assumption of the standard model that information in short-term memory is directly accessible.

Tehan and Humphreys (1996) asked their participants to remember the second of two four-item blocks. For example, the first block might be “jail silk orange peach” and the second block might be “page leap carrot witch”.

The participants showed better short-term memory for the word “carrot” when asked to recall the vegetable from the second block than when asked to recall the type of juice from the second block.

This occurred because there was more proactive interference from the words in the first block in the latter condition (orange is a type of juice). Thus, recall from short-term memory depends on the nature of the retrieval cue (e.g., vegetable; type of juice), and information in short-term memory is not always directly accessible.

Evaluation

The standard model provides a simple account of short-term memory. However, most of its assumptions are incorrect or only partially correct. Nairne (2002a, p. 76) summarized its limitations:

• It leads one to the conclusion that forgetting rates are fixed, like gravity, rather than variable, as much of the data suggest.

• It also suggests that the main vehicle for short-term storage is rehearsal when, in fact, much of the variability in immediate retention turns out to be independent of rehearsal.
• Finally, it leads one to the conclusion that remembering is a direct byproduct of activation … It is the interpretation of that activation, through a cue-driven retrieval process, that explains how we remember over the short term.