Stroop interference: An input and an output phenomenon

Three theories of Stroop interference are considered: perceptual conflict theory (Hock and Egeth, 1970), response competition theory (Morton, 1969) and conceptual encoding theory (Seymour, 1977). The first two fail to provide a full explanation of the available data, and Seymour's evidence is incomplete. Two experiments are reported. In the first, typical Stroop interference occurs in naming colour patches. In the second, subjects responded to colour patches with learned letter name responses. Both stimulus-related (incongruent colour names) and response-related (incongruent letters) distractors produced interference. These results indicate that any theory which assumes only a single locus for interference is incomplete. Conceptual encoding conflict and a modified form of response competition are suggested as possible dual mechanisms for Stroop interference effects.