The effect is named after John Ridley Stroop, who published the effect in English in 1935 in an article entitled Studies of interference in serial verbal reactions that includes three different experiments. However, the effect was first published in 1929 in German, and its roots can be followed back to works of James McKeen Cattell and Wilhelm Wundt in the nineteenth century.
In his experiments, J. R. Stroop administered several variations of the same test for which three different kinds of stimuli 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.
In the first experiment, 1 and 2 were used. The task required the participants to read the written color names of the words independently of the color of the ink (for example, 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.
Stroop identified a large increase in 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 (it reads the word "red" and...
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