A more complicated explanation follows, but simply put, the McGurk effect happens when our eyes tell our ears what they’re hearing. It’s a wonderful demonstration of how vision and hearing are paired in language. In the the video that follows, the language that is ‘seen’ is the movement of the mouth. As we know, spoken words include both the sound component as well as the visual elements of how the lips and face move. In the end, vision must agree with what is said, if there is a disagreement, the eyes overrule the ears.
From: http://en.wikipedia.org/wiki/McGurk_effect May 24, 2013:
“The McGurk effect 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.[1] The visual information a person gets from seeing a person speak changes the way they hear the sound.[2] People who are used to watching dubbed movies may be among people who are not susceptible to the McGurk effect because they have, to some extent, learned to ignore the information they are getting from the mouths of the “speakers”.[3] If a person is getting poor quality auditory information but good quality visual information, they may be more likely to experience the McGurk effect.[4] Integration abilities for audio and visual information may also influence whether a person will experience the effect. People who are better at sensory integration have been shown to be more susceptible to the effect.[2] Many people are affected differently by the McGurk effect based on many factors, brain damages or disorders.”