Textbook of Usability

Also known as: short-term memory, STM

Working memory is the cognitive system that holds and manipulates information currently in use. It is the mental workspace where reasoning, comprehension, problem-solving, and decision-making take place. Its defining characteristic is severely limited capacity.

Classic estimates from George Miller (1956) put working memory at about 7 ± 2 items, but more rigorous experiments by Nelson Cowan (2001) have revised this downward: when chunking is controlled for, working memory holds only about 4 ± 1 independent items at a time.

Working memory also has limited duration. Without active rehearsal (mental repetition of the contents) information decays within approximately 15–30 seconds. Peterson and Peterson (1959) demonstrated this by having participants hold three consonants in mind while counting backward; recall dropped to near zero within 18 seconds.

Design implications follow directly:

• Never require users to remember more than ~4 items across screens
• Provide external memory aids (breadcrumbs, progress indicators, persistent status displays)
• Avoid split-attention designs that force mental integration of separated information
• Use chunking to extend effective capacity (phone numbers as 3-3-4 groups)
• Avoid interference by not presenting similar information that competes for the same mental resources

Working memory is arguably the single most important constraint on interface design.