Sensory memory is the brief, detailed trace of what you have just seen, heard or felt, lasting from a fraction of a second for sight to a few seconds for sound. It holds much more than you can report. Only the small part you pay attention to moves on to short-term memory; the rest fades or is overwritten by what comes next. Its two best-studied forms are iconic memory (vision) and echoic memory (hearing).

Sensory memory at a glance

  • Where it fits: the first stage of Richard Atkinson and Richard Shiffrin’s 1968 multi-store model, before short-term memory and long-term memory.
  • Capacity: large. It keeps a rich snapshot of the scene or sound, far more than the four or so items you can hold in working memory.
  • Duration: vision, well under a second; hearing, a few hundred milliseconds for the raw sound and several seconds for a more processed trace.
  • Control: automatic. You cannot choose to hold a sensory trace longer; you can only attend to part of it before it goes.
  • How it is measured: mainly with the partial-report method described below, plus brain recordings for hearing.

Iconic memory: Sperling’s letter experiment

The modern study of sensory memory starts with one clever experiment. In 1960 George Sperling flashed a grid of 12 letters (three rows of four) for 50 milliseconds. Asked to report everything, people managed only about four or five letters, yet they insisted they had seen more. So Sperling changed the question: just after the grid vanished, a high, middle or low tone told them which single row to report. They could now report most of the cued row, whichever it was, which implies that around nine of the 12 letters were briefly available. When the tone was delayed by about a second, the advantage disappeared and performance fell back to the whole-report level.

This is the partial-report method, and its logic is what matters: the information was there, but it faded faster than people could read it out. Ulric Neisser later named this visual store “iconic memory”. Max Coltheart’s 1980 review drew a useful distinction between visible persistence, the image still seeming to be there after it has gone, and informational persistence, the usable information you can still read out of it.

Echoic memory: why you can replay the last few words

Hearing has its own sensory store, and it lasts longer, which makes sense because sounds unfold over time and have to be held together to be understood. In 1972 Christopher Darwin, Michael Turvey and Robert Crowder ran an auditory version of Sperling’s task, playing letters and digits from three directions at once. A partial-report advantage appeared here too, and faded over roughly two to four seconds.

In a 1984 review, Nelson Cowan argued for two auditory stores: a short one of a few hundred milliseconds holding the sound much as it was heard, and a longer one of several seconds holding a partly processed version. The longer store is the one you notice in daily life, when someone asks “were you listening?” and you can still retrieve their last sentence.

The brain’s auditory trace can also be seen directly. In 1978 a team led by Risto Näätänen in Finland described the mismatch negativity, an electrical brain response that appears when a sound differs from the ones before it, even when the listener is attending to something else. It shows that the brain keeps a short-lived record of recent sounds to compare new ones against.

Touch, smell and taste: what is known

Popular summaries often list five kinds of sensory memory, one for each sense, each with a neat duration. The evidence is much less even than that. Vision and hearing have decades of partial-report and brain-recording studies behind them. Touch has some: in a 2008 study, Alberto Gallace and colleagues found that people could count only up to about three taps spread across the body, but could detect whether a cued location had been touched when up to five were presented, and that this tactile trace faded faster the more taps there were. Smell and taste have been studied far less in this way, so firm durations for “olfactory” or “gustatory” sensory memory should be read with caution.

Is iconic memory just an afterimage?

Partly, according to a 2008 study by Ilja Sligte, Steven Scholte and Victor Lamme at the University of Amsterdam. Using a change-detection task, they described three stages: an iconic memory with very large capacity, then a fragile short-term store lasting about four seconds that held at least twice as much as ordinary visual short-term memory, and finally the robust but limited store most textbooks describe. Iconic memory in their experiments depended on the afterglow on the retina and nearly vanished when that was removed; the fragile store did not. The picture of a single “icon” that simply fades is therefore too simple.

Why sensory memory matters

  • Seamless perception. Your eyes jump several times a second and you blink often, yet the world looks continuous; a brief store helps bridge the gaps.
  • Understanding speech. Words and sentences only make sense once several sounds are held together, which is what the echoic trace allows.
  • A gate for attention. Sensory memory captures almost everything; attention picks what goes further. Our pages on selective attention and inattentional blindness show what happens to the rest.

Sensory memory and IQ

How much a person can hold in iconic memory is not what an IQ test measures, and there is no good evidence that training it raises intelligence. But one measure of the earliest stage of seeing does relate to IQ. In an inspection time task, two lines of different length are flashed and then covered by a mask, and the question is how short the exposure can be while the person still says correctly which line was longer. Jennifer Grudnik and John Kranzler’s 2001 meta-analysis of 92 studies estimated the average correlation between inspection time and IQ at about −0.30, or −0.51 after correcting for measurement error and restricted samples: people who need shorter exposures tend to score higher. That is a moderate link, usually read as a sign that efficient early processing is one small part of intelligence, not as a test of it. Our guides to fluid and crystallized intelligence and the g factor explain what IQ scores do capture.

Trust and scope notes

This page summarises published research for general information, with figures taken from the studies listed below. It is not medical advice: problems with vision, hearing or memory that are new, worsening or worrying deserve a conversation with a doctor, and no online test can assess them. The IQ Revealed test is an online reasoning test of 40 original items for adults aged 18 and over; it is not a clinical assessment and it does not measure sensory memory or inspection time. Our guide to how IQ tests work explains what an online test can and cannot tell you.

IQ Revealed is not affiliated with, endorsed by or connected to the researchers, universities, journals or publishers named on this page. Names are used only to identify the research being described.