Effects of Stroop interference on categorical perception in simultaneous color discrimination

Two experiments were conducted to assess the effects of verbal interference on categorical perception. The task involved simultaneous color discrimination with no memory demands, and a concurrent Stroop task was employed as verbal interference. Exp. 1 demonstrated that categorical perception was eliminated by an incongruent color word (i.e., Stroop interference), but not by a congruent color word or nonword fixation crosses. Exp. 2 demonstrated that categorical perception decreased when the intensity of Stroop Interference was increased, and it increased when correct verbal coding was enhanced. These results provide further evidence that interfering with verbal coding disrupts categorical perception, suggesting that verbal coding has a crucial role in categorical "perception." It is also suggested that categorical perception could occur at the encoding or decision level but not at the storage or memory level. The possible mechanisms for categorical perception are also discussed.