Deaf Peoples' Brains Rewire to 'Hear' Touch and Sight

By Chelsea Whyte on July 11, 2012 10:37 PM EDT

deaf kids
Deaf people interpret sight and touch with the part of the brain that is normally reserved for processing sound. (Photo: Creative Commons: daveynin)

Losing one sense - sight, sound, or any other - can significantly shift the way the brain works. A new study finds that deaf people perceive touch with the part of the brain hearing people use for sound.

Christina M. Karns, a postdoctoral research associate in the Brain Development Lab at the University of Oregon, Eugene, and her colleagues used MRI imaging to capture the brain activity of deaf people when responding to touch. They found that losing the ability to hear can change how deaf people process touch.

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Using a specially designed headset which stimulates vision with a flash of light to the eye and calls on the sense of touch with puffs of air delivered to the eyebrow and cheeks, they compared the brain responses of 13 deaf participants with 12 hearing people stimulated with the headsets while undergoing an MRI scan, which reveals blood flow to active parts of the brain.

They found that unlike their hearing counterparts, the deaf participants were experiencing both the visual and touch cues using the part of the brain normally reserved for hearing - a place called the Heschl's gyrus in the auditory cortex.

"They really feel touch in their auditory cortex,"  lead  author Christina M. Karns told The Atlantic."What we found is, in people born deaf the hearing part of the brain processes touch and, to a lesser degree, vision. And this wasn't the case at all for the hearing people."

The researchers used previous knowledge of a perceptual illusion in hearing people known as a the 'auditory induced double flash', which happens when a single flash of light paired with two auditory events is perceived as multiple flashes of light. Imagine a flash of lightning followed by two short cracks - most hearing people would report they had seen two flashes of light because of the auditory cues.

When the researchers used a double-puff of air as the touch-based stimulus paired with a single flash of light, hearing people claimed to see only a single flash. But deaf subjects saw two flashes. The brain scans of those who saw the double flash showed higher activity in Heschl's gyrus. Deaf individuals with the highest levels of activity in the primary auditory cortex in response to touch also had the strongest response to the illusion.

"We designed this study because we thought that touch and vision might have stronger interactions in the auditory cortices of deaf people," said Karns, according to Medical Daily." As it turns out, the primary auditory cortex in people who are profoundly deaf focuses on touch, even more than vision, in our experiment."

"This research shows how the brain is capable of rewiring in dramatic ways," said James F. Battey, Jr., director of the National Institute of Deafness and Other Communication Disorders. "This will be of great interest to other researchers who are studying multisensory processing in the brain."

The researchers suggest that the finding could advance learning tactics for deaf people. They said that if touch and vision interact more in the deaf, touch could be used to help deaf students learn math or reading. 

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