(CBS/AP) Dyslexia may be a disorder not only of reading and writing but also of hearing.
A surprising new study shows that adults with dyslexia have a hard time recognizing voices.The finding fits with research to uncover the building blocks of literacy and how they can go wrong. The eventual goal: To spot kids at risk for dyslexia even before they open "Go, Dog, Go!" in kindergarten - instead of diagnosing dyslexia in a struggling second-grader.
"Everybody is interested in understanding the root cause of dyslexia, so we can intervene early and do something about it," says John Gabrieli, a Massachusetts Institute of Technology cognitive neuroscientist and the senior author of the study, which was published last week in the journal Science.
Dyslexia is thought to affect 8 percent to 15 percent of Americans. It's not a problem with intelligence or vision. Instead, it's language-based. The brain struggles with what's called "phonological processing" - being able to distinguish and manipulate sounds, like "bah" and "pah," that eventually have to be linked to written letters and words.
A graduate student in Gabrieli's lab wondered if dyslexia would impair voice recognition as well. After all, subtle differences in pronunciation help distinguish people.
How to test that? Previous studies showed it's easier to recognize voices if they're speaking your own language. So the researchers recruited English-speaking college students and young adults, half with dyslexia, half without. The volunteers watched animated characters - like a clown, a mechanic, a soccer player - speaking either English or Chinese, to get familiar with how they sounded.
Then came the test - to match a voice to its character. The volunteers correctly identified the Chinese speakers only about half the time, regardless of whether they had dyslexia. But when they heard English speakers, people with dyslexia still were right only half the time - while the non-dyslexics did far better, identifying 70 percent of the voices correctly.
The project raise the question of whether voice recognition is a problem in young children, too, says Florida State University psychology professor Richard Wagner, who studies how to identify dyslexia early.
Gabrieli says he plans to test 5-year-olds.
Today, researchers know that children who are more phonologically aware upon entering kindergarten have a better shot at easy reading. One way to check that: See how they're able to delete sounds from words - ask them to quickly say "cowboy" without the "boy." Wagner says a child who answers such tasks correctly probably is developing fine. One who fails doesn't necessarily have problems but merely could have misunderstood or not wanted to play along. He says more clear-cut methods are needed.
Differences in brain-processing show up even in infants, says Patricia Kuhl of the University of Washington, who studies how babies learn language.
A colleague in her lab tested how well babies distinguish "ah" and "ee" sounds between 7 and 11 months of age. Those who did best wound up with bigger vocabularies and better pre-reading skills, such as rhyming, by their fifth birthdays. That doesn't mean they'll go on to experience dyslexia, but it does show how very early development can play a role in reading-readiness.