Effects of response type and set size on Stroop color-word performance.

The effect of several procedural variables was investigated in a discrete-trials Stroop task. Undergraduate students identified the color of four types of stimuli (asterisks, words unrelated to color, and incongruent and congruent Stroop stimuli) using verbal responses, buttons labeled with color words, and buttons labeled with colors. Set size was manipulated by presenting 2, 3, 4, or 5 different colors in a given trial block. A significant Stroop effect occurred in the verbal response condition, the size of the Stroop effect was reduced in the word-button condition, and the Stroop effect was eliminated in the color-button condition. Increases in set size produced linear increases in response time but did not influence the size of the Stroop effect.