Stroop effect

In psychology, the Stroop effect is the delay in reaction time between neutral 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. A basic task that demonstrates this effect occurs when there is an incongruent mismatch between the word for a color (e.g., blue, green, or red) and the font color it is printed in (e.g., the word red printed in a blue font). Typically, when a person is asked to name the font color for each word in a series of words, they take longer and are more prone to errors when words for colors are printed in incongruous font colors (e.g., it generally takes longer to say "blue" in response to the word red in a blue font, than in response to a neutral word of the same length in a blue font, like kid). The effect is named after John Ridley Stroop, who first published the effect in English in 1935. The effect had previously been published in Germany in 1929 by Jaensch. 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.

Original experiment

The effect was named after John Ridley Stroop, who published the effect in English in 1935 in an article in the Journal of Experimental Psychology entitled "Studies of interference in serial verbal reactions" that includes three different experiments. However, the effect was first published in 1929 in Germany by Erich Rudolf Jaensch, and its roots can be followed back to works of James McKeen Cattell and Wilhelm Maximilian Wundt in the nineteenth century. In his experiments, Stroop administered several variations of the same test for which three different kinds of stimuli were created: names of colors appeared in black ink, names of colors in a different ink than the color named, and squares of a given color. In the first experiment, words and conflict-words 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 the font). In experiment 2, stimulus conflict-words and color patches were used, and participants were required to say the ink-color of the letters independently of the written word with the second kind of stimulus and also name the color of the patches. If the word "purple" was written in red font, they would have to say "red", rather than "purple". When the squares were shown, the participant spoke the name of the color. Stroop, in the third experiment, tested his participants at different stages of practice at the tasks and stimuli used in the first and second experiments, examining learning effects. Unlike researchers now using the test for psychological evaluation, Stroop used only the three basic scores, rather than more complex derivative scoring procedures. Stroop noted that participants took significantly longer to complete the color reading in the second task than they had taken to name the colors of the squares in Experiment 2. This delay had not appeared in the first experiment. Such interference were explained by the automation of reading, where the mind automatically determines the semantic meaning of the word (it reads the word "red" and thinks of the color "red"), and then must intentionally check itself and identify instead the color of the word (the ink is a color other than red), a process that is not automated. However, in the modern version of the Stroop task, participants are presented with a series of stimuli appearing randomly on a computer screen within a single session, such that a different Stroop stimulus is displayed on each trial. The participant is asked to respond to the ink color of each stimulus, either verbally or by pressing a designated key on the keyboard. The task typically consists of three experimental conditions: the congruent condition, the incongruent condition, and the neutral condition, which serves as a baseline.

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