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Stroop effect

In psychology, the Stroop effect is the delay in reaction time between congruent and incongruent stimuli.

The effect has been used to create a psychological test (the Stroop test) that is widely used in clinical practice and investigation. [1]


A basic task that demonstrates this effect occurs when there is a mismatch between the name of a color (e.g., "blue", "green", or "red") and the color it is printed in (i.e., the word "red" printed in blue ink instead of red ink). When asked to name the color of the word it takes longer and is more prone to errors when the color of the ink does not match the name of the color.


The effect is named after John Ridley Stroop, who first published the effect in English in 1935.[2] The effect had previously been published in Germany in 1929 by other authors.[3][4][5] The original paper by Stroop has been one of the most cited papers in the history of experimental psychology, leading to more than 700 Stroop-related articles in literature.[5]

Experimental findings[edit]

Stimuli in Stroop paradigms can be divided into three groups: neutral, congruent and incongruent. Neutral stimuli are those stimuli in which only the text (similarly to stimuli 1 of Stroop's experiment), or color (similarly to stimuli 3 of Stroop's experiment) are displayed.[7] Congruent stimuli are those in which the ink color and the word refer to the same color (for example the word "pink" written in pink). Incongruent stimuli are those in which ink color and word differ.[7] Three experimental findings are recurrently found in Stroop experiments.[7] A first finding is semantic interference, which states that naming the ink color of neutral stimuli (e.g. when the ink color and word do not interfere with each other) is faster than in incongruent conditions. It is called semantic interference since it is usually accepted that the relationship in meaning between ink color and word is at the root of the interference.[7] The second finding, semantic facilitation, explains the finding that naming the ink of congruent stimuli is faster (e.g. when the ink color and the word match) than when neutral stimuli are present (e.g. stimulus 3; when only a colored square is shown). The third finding is that both semantic interference and facilitation disappear when the task consists of reading the word instead of naming the ink color. It has been sometimes called Stroop asynchrony, and has been explained by a reduced automatization when naming colors compared to reading words.[7]


In the study of interference theory, the most commonly used procedure has been similar to Stroop's second experiment, in which subjects were tested on naming colors of incompatible words and of control patches. The first experiment in Stroop's study (reading words in black versus incongruent colors) has been discussed less. In both cases, the interference score is expressed as the difference between the times needed to read each of the two types of cards.[5] Instead of naming stimuli, subjects have also been asked to sort stimuli into categories.[5] Different characteristics of the stimulus such as ink colors or direction of words have also been systematically varied.[5] None of all these modifications eliminates the effect of interference.[5]

Cognitive development[edit]

In the neo-Piagetian theories of cognitive development, several variations of the Stroop task have been used to study the relations between speed of processing and executive functions with working memory and cognitive development in various domains. This research shows that reaction time to Stroop tasks decreases systematically from early childhood through early adulthood. These changes suggest that speed of processing increases with age and that cognitive control becomes increasingly efficient. Moreover, this research strongly suggests that changes in these processes with age are very closely associated with development in working memory and various aspects of thought.[22][23] The stroop task also shows the ability to control behavior. If asked to state the color of the ink rather than the word, the participant must overcome the initial and stronger stimuli to read the word. These inhibitions show the ability for the brain to regulate behavior.[24]

Stroop effect

In popular culture[edit]

The Brain Age: Train Your Brain in Minutes a Day! software program, produced by Ryūta Kawashima for the Nintendo DS portable video game system, contains an automated Stroop test administrator module translated into game form.[44]


MythBusters used the Stroop effect test to see if males and females are cognitively impaired by having an attractive person of the opposite sex in the room. The "myth" (that is, hypothesis) was disproved.[45] A Nova episode used the Stroop Effect to illustrate the subtle changes of the mental flexibility of Mount Everest climbers in relation to altitude.[46]

In industry[edit]

British automotive marque MINI released a vehicle with the turn signal indicator designed as arrows that are pointing the opposite way than the indicated turn signal is blinking.[47]

via PsyToolkit

Online lesson with online demonstration of the Stroop effect

An online test based on the Stroop effect will show the level of flexibility of the mind

Training the flexibility of the mind based on the effect of the Stroop