Stretching Your Mouth Affects What You Hear

Stretching Your Mouth Affects What You Hear
Depending on how a mechanical device pulls and tugs areas around the mouth, the volunteer will hear and interpret speech sounds differently
By Erica Westly Scientific American Magazine - May 28, 2009
Neuroscience textbooks typically portray the five senses as separate entities, but in the real world the senses frequently interact, as anyone who has tried to enjoy dinner with a stuffy nose can attest. Hearing and vision seem similarly connected, the most famous example being the “McGurk effect,” where visual cues, such as moving lips, affect how people hear speech. And now new research shows that touch can influence speech perception, too.
David Ostry, a neuroscientist with co-appointments at McGill University and the New Haven, Conn.–based speech center Haskins Laboratories, has been studying for years the relation between speech and the somatosensory system, the network of receptors in skin and muscle that report information on tactile stimuli to the brain. In his most recent study, published in the Proceedings of the National Academy of Sciences USA, he and two Haskins colleagues found that subjects heard words differently when their mouths were stretched into different positions. The results have implications for neuroscientists studying speech and hearing as well as for therapists looking for new ways to treat speech disorders.
In the study, a specially designed robotic device stretched the mouths of volunteers slightly up, down or backward while they listened to a computer-generated continuum of speech verbalizations that sounded like “head” or “had,” or something in between. When the subjects’ mouths were stretched upward, closer to the position needed to say “head,” they were more likely to hear the sounds as “head,” especially with the more ambiguous output. If the subjects’ mouths were stretched downward, as if to say “had,” they were more likely to hear “had,” even when the sounds being generated were closer to “head.” Stretching subjects’ mouths backward had no effect, implying a position-specific response. Moreover, the timing of the stretch had to match that of the sounds exactly to get an effect: the stretch altered speech perception only when it mimicked realistic vocalizations.