Sensory memory

Sensory memory is a brief persistence of information from a sensory event after that event has ended. It can make recently presented information available for selection even when a person cannot report every item at once. Visual sensory persistence is one case; the experimental task and modality must be specified before assigning a duration or capacity to sensory memory.

George Sperling's1960 experiments separated information available after a brief visual display from information that could be reported serially. Observers saw arrays of letters. In partial-report conditions, a tone after the display selected which row to report, rather than announcing that row before presentation. Delaying the selection cue reduced the advantage of partial report. The critical logic was that a cue given only afterward could select information from more of the display than immediate whole-report performance appeared to show.^[ref]

For an illustrative calculation, suppose three rows contain four letters each. Whole report yields four correct letters, while a randomly chosen row can be reported with three correct letters. If each row is equally likely to be cued and comparably accessible, partial report estimates $3\times 3=9$ letters available near cue time. This is an inference under a sampling model, not a claim that nine letters were spoken on a single trial.

The example explains why report length and available information can differ. It also limits the interpretation: a post-display advantage is not unlimited long-term retention, and delays, masking or response demands can change what remains accessible. Sensory memory is studied through such contrasts, rather than identified solely with a participant saying that a display still feels visible.