This paper is a preliminary study on brain responses evoked by audio-visual speech stimuli. Electroencephalographic measurements (EEG) were used to receive objective evaluation cues for the contribution of the visual modality to auditory perception. Incongruent McGurk speech tokens were built and presented among unimodal and congruent bimodal stimuli. A time frequency analysis was made to study the phase coherence of the trials. Additional presentation of facial movements on a computer screen to the test subject changes the low frequency (7-10Hz) activity. Some temporal delays for incongruent speech signals can be related to a P300 auditory potential, which is often observed when unexpected presentation events occur to a test subject.
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