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.