In psychology, the Stroop effect is a demonstration of the reaction time of a task. When the name of a color (e.g., "blue," "green," or "red") is printed in a color not denoted by the name (e.g., the word "red" printed in blue ink instead of red ink), naming the color of the word takes longer and is more prone to errors than when the color of the ink matches the name of the color. The effect is named after John Ridley Stroop who first published the effect in English in 1935. The effect had previously been published in 1929, but only in Germany. The original paper has been one of the most cited papers in the history of experimental psychology, leading to more than 700 replications. The effect has been used to create a psychological test (Stroop Test) that is widely used in clinical practice and investigation.

The Stroop Effect test can also be adopted to investigate shape naming effects on shape recognition.

The test has additionally been modified to include other sensory modalities and variables, to study the effect of bilingualism, or to investigate the effect of emotions on interference. A similar effect has also been observed in individuals with grapheme–color synesthesia, people who perceive colors when seeing certain numbers and letters. If a number or letter is presented to such an individual in a color other than what they would perceive, there is a delay in determining what color the character actually is.

See also:
https://www.juliantrubin.com/encyclopedia/psychology/stroop_effect.html
https://en.wikipedia.org/wiki/Stroop_effect

Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)