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Early Blindness Sharpens Sense of Sound

Brain compensate when vision loss occurs before age 2

WEDNESDAY, July 14, 2004 (HealthDayNews) -- Sighted people often marvel at the creative genius of blind musicians; the list notably includes pop superstar Stevie Wonder, who's been blind since birth.

Now a brief in the July 15 issue of Nature hints at a neurological explanation for such extraordinary talent.

Canadian researchers compared the hearing perception of people who lost their sight by age 2, individuals who went blind between the ages 5 and 45, and people with normal vision. The test involved listening to a series of two tones. For each set of tones, subjects had to determine whether the pitch was rising -- meaning the second sound was higher -- or falling.

"What we found at this task: Blind subjects are much better than the controls, but only if they became blind at an early age," said Pascal Belin, an assistant professor of psychology at the University of Montreal in Quebec.

People who lost their vision early outperformed those who lost it later or sighted subjects at all levels of difficulty, even when the speed of the change in tones was 10 times faster than that perceived by the sighted people.

The study shows a clear correlation between the age at which the subjects lost their sight and their auditory prowess. "The earlier they lost sight, the better they were at the test," Belin noted.

"I think its a very good and important study," said Dr. Gottfried Schlaug, director of the Music and Neuroimaging Laboratory at Beth Israel Deaconess Medical Center in Boston.

Blind people are known to be much better than sighted people at orienting themselves by sound. Schlaug offers this analogy: A sighted person who is stuck in traffic and hears a police car will look around to see where the sound is coming from; a blind person is much better able to localize the sound.

Now it seems that people who lose their sight early in life are also adept at distinguishing between tones when they are either close together in pitch or in succession.

"They can actually differentiate better whether or not this is a police car or a fire truck or something else," Schlaug said. "They're better at making fine discriminations based on the composition of the actual tone."

The authors suspect the brains of people who went blind as infants or toddlers compensate for the loss of sight by enhancing auditory performance. Scientists believe the capacity of the brain to reorganize itself, a phenomenon known as cerebral plasticity, is much greater in young children than in adults.

"The earlier a brain is challenged to adapt to a particular situation, the better it is, the more able the brain basically is to adapt," Schlaug agreed. On the other hand, he said stroke studies involving older adults have demonstrated the brain's ability to make needed modifications in that circumstance.

"It seems to be that plasticity is maybe faster and more efficient and will lead to better results if the injury is early in life, but we cannot conclude it doesn't happen later in life," he said.

Perhaps even the late "Father of Soul" Ray Charles benefited from the brain's remarkable capacity to turn a visual deficit into a musical achievement. Charles didn't begin to lose his sight until he was 5, becoming totally blind at age 7.

More information

Take the National Institute on Deafness and Other Communication Disorders' online survey to test your sense of pitch.

SOURCES: Pascal Belin, Ph.D., assistant professor, Department of Psychology, University of Montreal, Quebec; Gottfried Schlaug, M.D., Ph.D., director, Music and Neuroimaging Laboratory, Beth Israel Deaconess Medical Center, and associate professor, neurology, Harvard Medical School, Boston; July 15, 2004, Nature
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