LEFT AND RIGHT HEMIFIELD ADVANTAGES OF FUSIONS AND COMBINATIONS IN AUDIOVISUAL SPEECH-PERCEPTION

If a place-of-articulation contrast is created between the auditory an d the visual component syllables of videotaped speech, frequently the syllable that listeners report they have heard differs phonetically fr om the auditory component. These ''McGurk effects'', as they have come to be called, show that speech perception may involve some kind of in termodal process. There are two classes of these phenomena: fusions an d combinations. Perception of the syllable / da/ when auditory /ba/ an d visual /ga/ are presented provides a clear example of the former, an d perception of the string /bga/ after presentation of auditory /ga/ a nd visual /ba/ an unambiguos instance of the latter. Besides perceptua l fusions and combinations, hearing visually presented component sylla bles also shows an influence of vision on audition. It is argued that these ''visual'' responses arise from basically the same underlying pr ocesses that yield fusions and combinations, respectively. In the pres ent study, the visual component of audiovisually incongruous CV-syllab les was presented in the left and the right visual hemifield, respecti vely. Audiovisual fusion responses showed a left hemifield advantage, and audiovisual combination responses a right hemifield advantage. Thi s finding suggests that the process of audiovisual integration differs between audiovisual fusions and combinations and, furthermore, that t he two cerebral hemispheres contribute differentially to the two class es of response.