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Stroop effect

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Delay and disruption in naming the colours of words printed in non-matching coloured ink, as when the word red is printed in blue ink, the word blue in green ink, and so on. To perform the task it is necessary to ignore the meanings of the printed words and to respond only to the colours in which they are printed, but with experienced adult readers automatic processing tends to occur, causing interference in the processing of information and a significant (approximately 75 per cent) increase in the time required to name the colours, compared with the time taken to name the colours of meaningless strings of letters, and the effect cannot be suppressed voluntarily. The delay and disruption occur when naming the colours, but not when reading the words. This phenomenon provides a remarkable example of knowledge acting as a handicap: a person who could not read the words, through illiteracy or lack of knowledge of the language, for example, would not be slowed down. A commercial test of neuropsychological functioning based on this phenomenon is called the Stroop Neuropsychological Screening Test (SNST). A simple demonstration of it can be constructed with a colour printer, or even with coloured pens. Prepare a page of colour names, such as red, green, blue, and black, in random order, each name printed in one of those colours at random, and then prepare another sheet, identical apart from the fact that the colour names are changed to nonsense words by moving each letter forward one place in the alphabet, so that red becomes sfe, and so on; then ask people to name all the colours in which the words are printed as quickly as possible, and compare the average times for the two sheets. Compare flanker compatibility effect, Simon effect. [Named after the US psychologist J(ohn) Ridley Stroop (1897–1973) who first reported the effect in the Journal of Experimental Psychology in 1935]

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