He McGurk effect is a perceptual phenomenon in which the perception of a spoken sound is influenced by simultaneously presented visual information. For example, if you hear the sound /ba/ while viewing the image of someone moving their lips to pronounce the sound /ga/, the perception may be a combination of both sounds, perceiving something like /bga/.
You can test the effect with this video:
This effect was discovered by psychologist Harry McGurk and his colleague John MacDonald in 1976, who found that the perception of spoken sounds depends not only on auditory information, but also on simultaneously presented visual information. Since then, the McGurk effect has been the subject of numerous studies and has been shown to be a robust phenomenon that occurs in different contexts and with different languages.
One of the most interesting findings about The McGurk effect is that it appears to be involuntary and unconscious. That is, participants in the studies cannot help but experience the effect, even if they know that the visual information does not match the auditory information. This suggests that the McGurk effect occurs at an automatic level of perceptual processing, in which visual information influences sound perception without the person being aware of it.
Another important finding is that the McGurk effect occurs most frequently when visual and auditory information are congruent, that is, when the visual information coincides with the auditory information. For example, if you hear the sound /ba/ while viewing an image of someone moving their lips to pronounce the same sound /ba/, the perception will be stronger and clearer than if the visual and auditory information are incongruent.
Besides, The McGurk effect appears to be stronger in low-level or ambient noise situationssuggesting that visual information may be more important in these situations to aid speech perception.
In summary, The McGurk effect is an interesting phenomenon that demonstrates that speech perception depends not only on auditory information, but also on visual information that is presented simultaneously.. This effect has important implications for the understanding of speech perception and may have practical applications in the design of assistive listening technologies and in the rehabilitation of people with hearing impairments.