Attention to touch weakens audiovisual speech integration.

One of the classic examples of multisensory integration in humans occurs when speech sounds are combined with the sight of corresponding articulatory gestures. Despite the longstanding assumption that this kind of audiovisual binding operates in an attention-free mode, recent findings (Alsius et al. in Curr Biol, 15(9):839-843, 2005) suggest that audiovisual speech integration decreases when visual or auditory attentional resources are depleted. The present study addressed the generalization of this attention constraint by testing whether a similar decrease in multisensory integration is observed when attention demands are imposed on a sensory domain that is not involved in speech perception, such as touch. We measured the McGurk illusion in a dual task paradigm involving a difficult tactile task. The results showed that the percentage of visually influenced responses to audiovisual stimuli was reduced when attention was diverted to a tactile task. This finding is attributed to a modulatory effect on audiovisual integration of speech mediated by supramodal attention limitations. We suggest that the interactions between the attentional system and crossmodal binding mechanisms may be much more extensive and dynamic than it was advanced in previous studies.