Seeing and hearing others and oneself talk.

We studied the modification of auditory perception in three different conditions in twenty subjects. Observing other person's discordant articulatory gestures deteriorated identification of acoustic speech stimuli and modified the auditory percept, causing a strong McGurk effect. A similar effect was found when the subjects watched their own silent articulation in a mirror and acoustic stimuli were simultaneously presented to their ears. Interestingly, a smaller but significant effect was even obtained when the subjects just silently articulated the syllables without visual feedback. On the other hand, observing other person's or one's own concordant articulation and silently articulating a concordant syllable improved identification of the acoustic stimuli. The modification of auditory percepts caused by visual observation of speech and silently articulating it are both suggested to be due to the alteration of activity in the auditory cortex. Our findings support the idea of a close relationship between speech perception and production.