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Dyslexia involves difficulty with spoken language, study finds

By Carolyn Y. Johnson
Globe Staff / July 29, 2011

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Most people think of dyslexia as a reading problem, a learning disability that causes letters to get jumbled up. But research by MIT scientists suggests that an even more basic cognitive difference sets apart people with dyslexia: They have difficulty recognizing voices speaking their own language.

The finding, published yesterday in the journal Science, adds to the evidence that what underlies the reading difficulties in dyslexia may be fundamental problems in how the brain processes language, distinguishing words and speech sounds.

In general, people are better at linking a voice to a speaker when the person is talking in a language they understand.

The study found that nondyslexic English speakers presented with an array of cartoon characters, each with a different voice, were good at identifying which voice went with which character when they were speaking English and not as good when it came to Chinese.

But the surprise came when people with dyslexia were given the same task.

“We were struck by the severity,’’ said John Gabrieli, professor of cognitive neuroscience at MIT. “The [dyslexic] participants were high-functioning students, going to college, not children who avoided reading altogether.

“And yet their ability to learn to recognize one voice from another was no better for English than it was for Chinese. This just shows how substantial this difficulty really is.’’

The new research is intriguing, said Glenn Rosen, associate professor of neurology at Beth Israel Deaconess Medical Center.

Dyslexia has long been associated with reading, he said, because it is something the brain has to be taught to do, marshaling different brain regions to read a simple sentence, unlike spoken language, an ability children naturally acquire without much instruction.

“What this research and some other more recent findings are showing pretty clearly is dyslexics have difficulty in language in general,’’ Rosen said.

Gabrieli said future research will look at what brain regions are active in people with dyslexia and others when they are trying to recognize voices and whether people with dyslexia perform differently on other tasks, such as facial recognition.

Carolyn Y. Johnson can be reached at cjohnson@globe.com.

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