Stroop interference based on the multimodal correlates of haptic size and auditory pitch.

In a preliminary experiment subjects were asked to explore three wooden knobs of different sizes and to rate each one on a series of 7-point scales. The results confirmed that an object may possess a number of multimodal qualities that are contingent on its haptic size. The pattern of intercorrelations between the qualities was consistent with the pattern that is observed when subjects respond to pure auditory tones varying in pitch. For example, small (high-pitched) sounds, like small objects, are judged to be sharp, thin, light, weak, fast, tense, and bright. The main experiments used a paradigm based on the Stroop interference effect. Subjects were required to press one of two keys as quickly as possible depending on which of four possible words appeared in the centre of the screen. A 50 Hz or a 5500 Hz tone accompanied each test word, and subjects responded on two keys that differed in size. Subjects were found to respond more slowly when either the pitch of the incidental sound or the size of the key on which they responded was incongruent with the multimodal features represented by the test word. The results confirm that people are automatically and immediately sensitive to the multimodal features of a stimulus when direct sensory evidence for the features is absent.