Background

A very compelling demonstration of the influence of vision on speech perception was developed by McGurk and MacDonald (1976) and has come to be known as the McGurk effect. To demonstrate the McGurk effect, participants are shown a video of a person’s mouth saying monosyllabic sounds, such as “ba,” “da,” and “tha.” However, the audio component does not always match what the speaker’s mouth was saying when the syllables were recorded. That is, the video has been dubbed, and the sound track is simply “ba” over and over again. To be clear, the sound is “ba” but the movement of the mouth may signal “ga.” The question is, What would the participants hear? Would they hear what they heard or what they saw? Thus, the question McGurk and MacDonald were interested in was whether people would hear the sound track or what the mouth was doing. Strangely, but compellingly, when participants watch the video, they perceive the sounds as being different from what they actually hear (see Figure 12.9). In Figure 12.9, the observer is watching a mouth say “ga,” but the sound track is “ba.” However, the observer’s perceptual experience is that of hearing “da,” a perception different from the actual sound. In order to really understand the McGurk effect, though, you have to hear it and see it for yourself.

In addition you can see an example from YouTube here .

On the McGurk Video tab you can place a video where the speaker is saying "da" but the audio is saying "ba". What does it sound like? On the Audio Track tab you can play just the sound from the original video. What do you hear? On the Original Video tab you can play the orginal video and see wht the person is realy saying.

McGurk Video

Here is the full McGurk effect video. What is the person saying? Start the video and watch the speaker. The video will look. After awhile, close your eyes and see what you hear. This effect seems to be most effective using the speakers so, if possible, do not use headphones.

Audio Track

Here is the audio from the McGurk video. It is clear that the sound says "ba".

Original Video

Here is the original, unedited, video. The speaker is clearly saying "da".