Mystifying the Senses: Bimodal Speech Perception :: Biology Essays Research Papers

Mystifying the Senses: Bimodal Speech Perception My grandmother, like many elderly people, suffers from hearing loss. Recently however, she has begun to lose her sight as well. Curiously enough, though her level of auditory impairment remains the same since macular degeneration has claimed her ability to see, her hearing seems to have deteriorated further. Could this be simply the result of alienation because of the loss of a further sense? This situation led me to wonder about my own hearing ability. I have often experienced hearing difficulty in settings where I cannot see the person who is talking to me-in a movie theater, or over the telephone. The questions raised here call into question the conventional notion of sensory processing. Distinctive inputs are received by their respective processing organ and the end result is relayed to the brain. How then can we explain a seeming reliance of two different sensory percepts on each other? Is there more to hearing than our ears? Historically, scientific evidence for the existence of sensory integration has long existed, but the first formal theory developed to this effect was stumbled upon by Harry McGurk and John MacDonald of the University of Surrey (1). The scientists were involved in a study of how infants perceive speech by playing a video of a mother talking in one place and playing the sound of her voice in another place. They randomly began to play with the consequences of dubbing an particular audio sound onto the video of the mother saying a different sound (2). They found that when the auditory syllable, "ba-ba" was imposed on the visual syllable "ga-ga", "da-da" was heard. The same occurred when the audio and visual syllables were reversed. Also, "pa-pa" dubbed on "ka-ka" was heard as "ta-ta". When one of the sensory inputs was eliminated by closing the eyes, or plugging the ears, the correct syllable was identified (2). McGurk and McDonald found "Contemporary, auditory-based theories of speech p erception...inadequate to accommodate these new observations" and concluded that there must be some allowance made for the influence of the visual on hearing (2). The conventional theory of the senses is challenged. So, speech perception is bimodal. Of course, as science repeatedly shows, nothing is simple as that. The question remains, how does this integration occur? When does it occur? What neurological systems are involved? It has become generally accepted that audio and visual inputs are received by independent organs (the ears and eyes) and that integration occurs sometime after these two systems have "processed" the input.