One classical example of how vision and audition come together is speech perception. Although we tend to think of speech as a purely auditory process, it is surprisingly sensitive to visual influences. This is quite evident when we try to follow a conversation in a noisy place, as listeners tend to look at the talker's lip movements--especially as we grow older and our hearing declines. Classical experiments revealed that if a heard "ba" syllable is dubbed to a talker seen to be saying "ga," the observer often "hears" "da"--a sound that has the characteristics of both the heard and seen speech but is different from either. This illusion, first reported by Harry McGurk in 1976, is so powerful that observers usually do not realize what has happened until they look away from the talker--at which point the illusion breaks up and the true auditory event ("ba") is heard.
The currently accepted view on the McGurk illusion and similar multisensory-integration phenomena is that so-called binding processes in the brain occur pre-attentively; that is, they occur automatically and unavoidably as long as the perceiver has access to both input channels. In the new study, the researchers tested this "automaticity" hypothesis directly by making observers perform a difficult task (an atte
Contact: Heidi Hardman