Generalization of the generation of an MMN by illusory McGurk percepts: voiceless consonants

Objective: The existence of a Mismatch Negativity (MMN) evoked by McGurk percepts elicited by audiovisual syllables with constant auditory components has been previously demonstrated with voiced consonants [Clin. Neurophysiol. 113 (2002) 495]. The present study aimed at generalizing such results with voiceless consonants. In a first experiment, the MMN was computed using the classical subtraction method (standard minus deviant). Since results showed a possible contamination by exogenous visual components, a technique preventing from including those components in the differential waveform was used in a second experiment (deviant in sequence minus deviant presented alone). Methods: Cortical evoked potentials were recorded using the oddball paradigm on eight adults in three experimental conditions (auditory alone, visual alone and audiovisual) for experiment one and in two conditions (visual alone and audiovisual) for experiment two. Obtaining illusory percepts was confirmed in additional psychophysical experiments. Results: Significant MMNs were recorded in the three conditions of experiment one, whereas only the audiovisual condition of experiment two gave rise to a significant MMN. Conclusions: Provided that the MMN is computed with deviant stimuli only, the present results confirm the elicitation of genuine audiovisual MMN. Possible refractoriness effects and N2b confound have, however, to be controlled for in further studies.