The sensory memory for visual stimuli is sometimes known as the iconic memory, the memory for aural stimuli is known as the echoic memory, and that for touch as the haptic memory. Indeed, it lasts for such a short time that it is often considered part of the process of perception, but it nevertheless represents an essential step for storing information in short-term memory. Sensory memory is an ultra-short-term memory and decays or degrades very quickly, typically in the region of 200 - 500 milliseconds (1/5 - 1/2 second) after the perception of an item, and certainly less than a second (although echoic memory is now thought to last a little longer, up to perhaps three or four seconds). Unlike other types of memory, sensory memory cannot be prolonged via rehearsal. As information is perceived, it is therefore stored in sensory memory automatically and unbidden. The brain is designed to only process information that will be useful at a later date, and to allow the rest to pass by unnoticed. This does not require any conscious attention and, indeed, is usually considered to be totally outside of conscious control.

The stimuli detected by our senses can be either deliberately ignored, in which case they disappear almost instantaneously, or perceived, in which case they enter our sensory memory. Thus, distractions or divided attention during initial learning may severely impair subsequent retrieval success, whereas distractions at the time of recall may slow down the process a little, but has little to no effect on its accuracy. Studies have shown that attention significantly affects memory during the encoding phase, but hardly at all during recall. For example, the ability to look at something and remember what it looked like with just a second of observation is an example of sensory memory. It acts as a kind of buffer for stimuli received through the five senses of sight, hearing, smell, taste and touch, which are retained accurately, but very briefly. It is the ability to retain impressions of sensory information after the original stimuli have ended. Sensory memory is the shortest-term element of memory.

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