Deaf people perceive touch differently than hearing people, says a new National Institutes of Health study.
In people who are born deaf, brain adapts to survive in a sound-less world. The region of the brain dedicated to processing sounds takes up the function of processing touch while the region that processes vision gets stronger than in hearing people.
"This research shows how the brain is capable of rewiring in dramatic ways. This will be of great interest to other researchers who are studying multisensory processing in the brain," said James F. Battey Jr., director of the NIDCD.
For the study, researchers hooked up the participants' brain to special MRI scanners that could be worn like headphones. Researchers delivered small puffs of air above the participants' right eyebrow and right cheeks. Small fiber optic cable was placed just below the air nozzle. Together both the air puffs and light flashes worked to send touch and visual signals to the brain. The researchers wanted to know how the brain reacts to these stimuli.
They used a phenomenon called as "auditory induced double flash". This is a kind of perceptual illusion, where a single light flash followed by two sound stimuli is perceived as double light flash in hearing people.
People who could hear reported that they saw only one flash of light when the researchers gave two puffs of air and one flash of light whereas, people who couldn't hear saw two flashes of light.
Brain scans of deaf people showed that there was higher activity in the Heschl’s gyrus - the brain's primary auditory cortex site.
Not all deaf people had the same level of activity in the brain regions for sound but those who had increased activity said that they saw two flashes of light.
"We designed this study because we thought that touch and vision might have stronger interactions in the auditory cortices of deaf people. As it turns out, the primary auditory cortex in people who are profoundly deaf focuses on touch, even more than vision, in our experiment," said Dr Christina M. Karns, Ph.D., a postdoctoral research associate in the Brain Development Lab at the University of Oregon, Eugene.
The study could help deaf people in many ways. When a child born with deafness is given implants that could enable them to hear sounds, the brain is confused because it has already changed pathways to auditory regions. Now, researchers can find out how much the brain has changed and how it can be re-trained to react to sound stimuli. Also, children who are deaf since birth can be taught math and reading skills by techniques that employ touch and vision more than sounds.