McGurk Effect
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. The visual information a person gets from seeing a person speak changes the way they hear the sound.
Origin
Harry McGurk and John MacDonald discovered the effect accidentally in 1976 while studying infant language perception at the University of Surrey. A technician had dubbed audio "ba" onto footage of someone mouthing "ga"; when played back, both researchers perceived "da." Their paper "Hearing Lips and Seeing Voices" appeared in Nature on 23 December 1976 and has since been cited over 4,800 times, establishing that speech perception is fundamentally audiovisual.