Psychological distance and reaction time in a Stroop task.

Several sources of interference may simultaneously affect the onset of the well-known "Stroop effect." Among them is the semantic component, which is reflected in the gradient or semantic effect. This effect consists of an increase in the amount of interference as the semantic distance between the word and the color concept decreases. Shepard (Science 237:1317-1323, 1987) relates psychological space, measured through multidimensional scaling, to mean response times. The present investigation aims to study the function relating the semantic gradient with the psychological distance between the word and the color in a Stroop task. After measuring the gradient, we obtained the subjective rating of the degree of dissimilarity of the gradient words with the concept of "color." In our work, we show that the amount of interference in a Stroop task increases when the semantic distance from the word to the color concept decreases, and it does so exponentially. We replicated the study with different stimuli to test the robustness of the results.