Stroop effect

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In psychology, the Stroop effect is a demonstration of the reaction time of a task. When a word such as blue, green, red, etc. is printed in a color differing from the color expressed by the word's semantic meaning (e.g. the word "red" printed in blue ink), naming the color of the word takes longer and is more prone to errors than when the meaning of the word is congruent with its ink color. The effect is named after John Ridley Stroop who first published the effect in English in 1935.^[1] The effect had previously been published in 1929, but only in German. ^[2][3][4] The original paper has been one of the most cited papers in the history of experimental psychology, leading to over 700 replications.^[4]

The effect has been used to create a psychological test which is widely used in clinical practice and investigation. The test has also been further modified to investigate very different phenomena.^[4]

[edit] Original experiment

Figure 1 from experiment 2 of the original description of the Stroop effect (1935). 1 is the time that takes to name the color of the dots while 2 is the time that takes to say the color when there is a conflict with the written word; which takes longer.^[1]

The effect was first published in 1929, but only in German^[2][3][4]. However, it is named after John Ridley Stroop, who published the effect in English in 1935 in an article titled Studies of interference in serial verbal reactions which includes three different experiments.^[1]

In the experiments he administered several variations of the same test for which three different kind of stimulus were created. In the first one names of colors appeared in black ink. In the second names of colors appeared in a different ink than the color named. Finally in the third one there were squares of a given color.^[1]

In the first experiment stimulus 1 and 2 were used. The task consisted in the participants having to read the written color names of the words independently of the color of the ink; for a given word; such as "purple" they would have to read "purple" no matter what the color of its ink was. In the second experiment stimulus 2 and 3 were used and participants were required to say the color of the letters independently of the written word with the second kind of stimulus and also name the color of the dot squares. If the word "purple" was written in red they would have to say "red"; but not "purple"; when the squares were shown the participant would have to say its color. Stroop in the third experiment tested his participants at different stages of practice at the tasks and stimulus used in the first and second experiments, to account for the effects of association.^[1]

Stroop identified a large increase on the time taken by participants to complete the color reading in the second task compared to the naming of the color of the squares in experiment 2 while this delay did not appear in the first experiment. Such interference was explained by the automation of reading, where the mind automatically determines the semantic meaning of the word, and then must override this first impression with the identification of the color of the word, a process which is not automatized.^[1]

As opposed to the Stroop test most commonly used in psychological evaluation,^[5] J.R Stroop never compared the time used for reading black words and the time needed for naming colors that conflicted with the written word.

[edit] Modifications

The original paper of the Stroop effect has been one of the most cited papers in the history of experimental psychology, leading to over 710 replications.^[4] The test has been further modified to investigate very different phenomena.

In the study of interference the most commonly used procedure has been similar to Stroop's second experiment, in which subjects are tested on naming colors of incompatible words and of control patches; however the first experiment (reading words in black versus incongruent colors) has received much less interest. In both cases the interference score is expressed as the difference between the times needed to read each of the two types of cards.^[4] Usually lists of stimulus are used, but time measures for individual words permit more control on research variables.^[4] Rather than naming or reading stimuli aloud, subjects have also been asked to sort stimuli into categories.^[4] Different characteristics of the stimulus such as ink colors or direction of words have also been systematically varied.^[4] None of all these modifications eliminates the effect of interference.^[4]

The Stroop task has been employed to study frontal function and attention in brain imaging studies.^[6] Speaking is not possible in the scanner because it moves the head, so a number theme is often used instead. For instance, three words may be displayed that read "two" and the participant must press three on their button box.^[7]

The test has additionally been modified to include other sensory modalities and variables,^[8] to study the effect of bilingualism,^[9] or to investigate the effect of emotions on interference.^[10] 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.^[11]

[edit] Clinical use

The stroop effect has been used to investigate the psycological capacities of a person since its discovery; while during the twentieth century it also became a popular neuropsychological test.^[12]

The most commonly used Stroop test in clinical settings consists of three different subtasks; each one similar to the ones used in the original work by Stroop. The first subtask consists in reading color names written in black ink (similar to the first group of stimulus of the original Stroop article). The second subtask consists in saying the color of the ink of groups of letters "X" (similar to the third group of stimulus of the original Stroop article) so no reading is needed; the third, with written color names differing from the ink used (similar to the second group of stimulus of the original Stroop article), consists in saying the color of the ink and not the written word.^[5] Other formats varying the number of subtasks, stimulus or times for the task are also used in clinical practice.^[12] The main score is the number of correct words named in the given time for each of the subtasks .^[5][13]

This test is considered to measure concentration effectiveness as well as processing speed;^[12] and it is commonly part of executive functions test batteries. It has been used to investigate cognitive aspects of disorders such as brain damage,^[12] Attention Deficit Hyperactivity Disorder,^[14], dementias, or mental disorders.

[edit] Anatomical basis

EEG and fMRI studies of the Stroop effect have revealed selective activation of the anterior cingulate cortex during a stroop task, a prefrontal structure (see frontal lobe) in the brain which is hypothesized to be responsible for conflict monitoring.

[edit] In popular culture

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.^[15] A Nova episode used the Stroop Effect to illustrate the subtle changes of the mental flexibility of Mount Everest climbers in relation to altitude.^[16]

[edit] References