Textbook of Usability

Sensory memory is the earliest stage of memory, a brief high-fidelity trace that holds sensory information for a fraction of a second before either transferring to working memory or being lost. Each sense has its own sensory store:

• Iconic memory (vision): lasts approximately 250–500 milliseconds
• Echoic memory (hearing): lasts approximately 2–4 seconds
• Haptic memory (touch): lasts approximately 2 seconds

George Sperling's classic 1960 experiments demonstrated iconic memory by showing subjects arrays of 12 letters for just 50 ms. Subjects could report only 4–5 letters, but when cued (immediately after the display) to report a specific row, they could report almost any row perfectly — proving that all 12 letters had been held in iconic memory, but the trace decayed before they could all be reported.

Sensory memory has enormous capacity but extremely brief duration. Information that is not attended to and transferred to working memory within a few hundred milliseconds is lost.

Design implications:

• Transient displays (brief tooltips, flashed notifications) may never reach conscious awareness
• Information the user needs should persist long enough for transfer to working memory — at minimum several seconds
• Abrupt screen transitions can overwrite iconic traces before they can be consolidated, causing users to lose track of what they had "just seen"