The McGurk effect was first described in 1976 in a paper by Harry McGurk and John MacDonald entitled “Hearing Lips and Seeing Voices”, and is a perceptual phenomenon that demonstrates an interaction between hearing and vision in speech perception. The illusion occurs when the auditory component of one sound is paired with the visual component of another sound, leading to the perception of a third sound. Not everyone is susceptible to the McGurk effect.
McGurk H, MacDonald J., “Hearing lips and seeing voices”, Nature. 1976 Dec 23-30;264(5588):746-8.