The basis of Stroop interference involving the multimodal correlates of auditory pitch.

A pure auditory tone has a range of multimodal qualities that are determined by its pitch. A reaction-time task was used to demonstrate that subjects respond immediately and automatically to these qualities. Subjects were required to press one of two keys depending on which word, from a limited set, appeared on a microcomputer screen. The words were antonyms that represented multimodal stimulus qualities, and they were assigned to alternative responses so that the two words that shared the same response were correlated in the same way with pitch. As an incidental stimulus, either a 50 Hz tone or a 5500 Hz tone accompanied the presentation of each word. Subjects were found to respond more slowly when the multimodal qualities of the tone were incongruent with the qualities represented by the test word. When the stimulus-response mapping rules were changed, however, the Stroop effect did not occur; suggesting that a polarised semantic code of the incidental tone, that embraces its multimodal features, accesses the same semantic register as the equivalent code for the test word itself.