Listening with eye and hand: cross-modal contributions to speech perception.

Three experiments investigated the "McGurk effect" whereby optically specified syllables experienced synchronously with acoustically specified syllables integrate in perception to determine a listener's auditory perceptual experience. Experiments contrasted the cross-modal effect of orthographic on acoustic syllables presumed to be associated in experience and memory with that of haptically experienced and acoustic syllables presumed not to be associated. The latter pairing gave rise to cross-modal influences when Ss were informed that cross-modal syllables were paired independently. Mouthed syllables affected reports of simultaneously heard syllables (and vice versa). These effects were absent when syllables were simultaneously seen (spelled) and heard. The McGurk effect does not arise from association in memory but from conjoint near specification of the same causal source in the environment--in speech, the moving vocal tract producing phonetic gestures.