Short term memory
A Working memory (WM) aka "primary" memory, "short-term" memory, "active" memory
Capacity (or capacities) for holding in mind, in an active, highly available state a small amount of information.
Short-term is:
- Recently derived from processing of sensory input
- Recently retrieved from long-term memory
- Recently generated by ongoing operations
Functions of short-term memory:
- To control ongoing and imminent actions
A Nature journal article suggests that short term memory is associated with the posterior parietal cortex. [1]
Widely accepted theory is that human working memory can hold on average five to nine concepts at a time varying with each person. This view was first expounded by George A. Miller in the seminal paper "The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information." [2] (1956; The Psychological Review, vol. 63 pp. 81-97); the exact range of the number is still open to some debate.
It is important to note the distinction between a concept and let's say a number or word. Concept can be anything, from a number to a word to an abstract meaning. For example, the numbers 684804791 might feel overwhelmingly difficult to remember, but separing them to 684, 804 and 791 and assigning a (meaningful) mental image to each one, or an auditory tone for each (as the set of numbers is pronounced, the task could require just three slots in working memory instead of 12. Similarly a sentence, and its meaning, is easier and more useful to remember than all the invidual words, which just proves that memory doesn't have to work by just storing invidual letters, words or sentences. There's no limit to what kind of concepts it can hold.
Working memory holds concepts only for a limited amount of time. To overcome this, a person might repeat a certain word or a phone number aloud or mentally (known as rehearsal), to be able to recall it later. Alternately the person might repeat the number aloud continuous until the task requiring the information -- such as finding a piece of paper and scribbling down the important phone number -- is complete. This keeps the concept in working memory.
Information from the working memory gets transferred to the long-term memory. The theory is, that it is not actually the amount of repetition that triggers this process. In fact, the meaningfulness, and the interconnectedness of the information is more important. In practical terms, continuous repetition of foreign language words might be very inefficient. Instead, thinking of more creative ways to connect the foreign words to their native counterparts, such as mental images connecting the two words, is far more rewarding.
Arguments that WM is distinct from long-term memory come from:
- Introspection
- Physiology
- Consideration of computational utility
- Effects of brain damage
- Experiments on normal subjects
Attempts to model short-term and long-term memory and the relations between them have given rise to theories such as the Model-Human Processor (detailed in ``The Psychology of Human-Computer Interaction``; Card, Moran and Newell, 1983), and projects to computationally describe these relations, such as ACT-R [3].