Stroop Effect

What Causes Interference?

For 40 years, Stroop interference was explained as a kind of “horse race” with the wrong horse (the word) beating the right one (the color) to the stage where a response was prepared—a serial/sequential processing explanation. Thirty to 40 years ago, investigators began to suggest that interference results from performing a controlled process (color naming) simultaneously with an automatic process (word reading)—a parallel processing explanation. Then, about 20 years ago, with the advent of neural network (connectionist) models, emphasis shifted to the idea that learning occurred via changes in stimulus-response connection strength. In the last 10 years, theories have integrated the Stroop effect into larger scale models of perceptual processing or language processing, situating interference in broader cognitive perspective. These increasingly sophisticated models successfully encompass the many published results that constitute the empirical database for the Stroop effect.

Features of the Stroop Effect

After 75 years, we know a very considerable amount about the Stroop effect and, consequently, about the interference that arises when attention is not entirely successful—when ignoring fails. Critically, we know that interference is most likely to occur when there is disparity in practice on the two dimensions. Yet in studies where the color information has been presented sufficiently before the word to give the color response a head start, the Stroop effect does not “flip over,” such that the color begins to interfere with reading the word. So relative speed of processing each dimension (word and color) is not the whole story. But there are also empirical challenges to the automaticity explanation, such as the finding that introducing an additional word—not a color word—into the display reduces the interference. If reading is automatic, why should adding another word dilute the interference?

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