The McGurk Effect is a perceptual phenomenon named after Scottish psychologist Harry McGurk, who was also co-author of the first article on the phenomenon, titled “Hearing Lips and Seeing Voices” which was published in Nature journal in 1976. The phenomenon involves an interaction between visual and auditory perception in speech. This occurs when sound of a speech does not match with the shape of the lips that produce that sound, thereby leading to perception of a word that actually has not been spoken at all. The best example would be when the video image of a person saying bay is dubbed with a sound corresponding to the usual pronunciation of the word gay causing the listener to perceive an intermediate word day. The brain, in this case, combines the auditory part of one sound with the visual perception of another sound, which ultimately results in the perception of a sound that was not even uttered. The phenomenon takes place when the listener is in a crowded room or when the speaker is speaking very softly and the former cannot hear the sound that well. The McGurk effect demonstrates that visual channel sends critical information not just to the people who are deaf but also to the listeners who can hear normally.
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