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iconic store


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One of the sensory registers, allowing a visual image to persist for about half a second (depending on brightness) after its stimulus has ceased. It enables television, which presents 25 still images per second, each given twice to raise the flicker rate to 50 per second (British standard), to convey the illusion of a single continuous image, which, owing to apparent movement, can be perceived as a moving image. In 1740, the Hungarian physicist Johann Andreas von Segner (1704–77) was the first to measure the duration of iconic memory traces (about half a second) by attaching a glowing ember to the rim of a wheel and determining the minimum speed of rotation (about 120 revolutions per minute) at which a complete circle was perceived. Interest in iconic memory was revived by a classic experiment devised by the US psychologist George Sperling (born 1934) and reported in the journal Psychological Monographs in 1960 in which three rows of four random letters were exposed for approximately 50 milliseconds; when viewers attempted to recall as many letters as possible from all three rows, they typically reported no more than four or five items, but when they attempted to recall as many letters as possible from a single specified row, cued after the offset of the display, their recall was virtually perfect, provided that the row number was cued immediately, but recall declined steadily with increasing cue delay up to about 500 milliseconds, suggesting (in line with von Segner's earlier finding) that more information is available immediately after the stimulus offset than can be reported before it fades from memory and that much of it has disappeared after about half a second. Also called iconic memory, a term introduced by the German-born US psychologist Ulric (Richard Gustav) Neisser (born 1928) in his book Cognitive Psychology (1967). See also sensory memory. Compare echoic store. [From Greek eikon an image+-ikos of, relating to, or resembling]

Subjects: Psychology.


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