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 which demonstrates an interaction between hearing and vision in speech perception. The illusion occurs when the auditory component of one sound (such as a spoken word) is paired with the visual component of another sound, leading to the perception of a different sound than the one presented. Not everyone is susceptible to the McGurk effect.

Source:

McGurk H, MacDonald J., “Hearing lips and seeing voices”, Nature. 1976 Dec 23-30;264(5588):746-8.