Speech perception is more than auditory perception. People attend to visual information, such as lip movements and facial gestures associated with speaking, as well as to the actual auditory information, or spoken words.

In the 1970s, Harry McGurk and John MacDonald presented research participants with videotapes with different spoken syllables, such as "ba" and "ga" dubbed over the original pronunciations. Instead of perceiving either the visual stimulus or the auditory stimulus, people perceived speech that was somewhere in between the two syllables.

The predominant explanation for this effect is that the brain attempts to integrate the auditory and visual stimuli in a way that best represents each stimulus.

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