Integration of Dichotically and Visually Presented Speech Stimuli

In dichotic listening, two competing messages are delivered to the left and right ear, respectively. Right-handed subjects tend to report hearing more frequently the message input to the right ear. This is called Right Ear Advantage (REA). When intensities and other properties of the messages are properly adjusted, subjects may have a single perception localized to the center of the head. Frequently the two stimuli ‘fuse’ and the resultant perception corresponds to neither of the presented stimuli. In a similar vein, in audiovisual speech perception discordant auditory and visual components of the stimulus may fuse (the McGurk effect). In the present study, we investigated the relationship between dichotic listening and audiovisual speech perception. Our results demonstrated REA and dominance of acoustical /ta/ stimulus. The influence of visual speech on the perception was clearly stronger than REA. When visual information was concordant with the auditory input to one ear, the perception of that syllable increased strongly, irrespective of the ear of stimulation. Interestingly, REA appeared even when visible speech modified perception.