Study Sheds Light on Auditory Role in Dyslexia
By PAM BELLUCK
Published: August 1, 2011
MANY PEOPLE CONSIDER DYSLEXIA simply a reading problem in which children mix up letters and misconstrue written words. But increasingly scientists have come to believe that the reading difficulties of dyslexia are part of a larger puzzle: a problem with how the brain processes speech and puts together words from smaller units of sound.
Now, a study published last week in the journal Science suggests that how dyslexics hear language may be more important than previously realized. Researchers at the Massachusetts Institute of Technology have found that people with dyslexia have more trouble recognizing voices than those without dyslexia.
John Gabrieli, a professor of cognitive neuroscience, and Tyler Perrachione, a graduate student, asked people with and without dyslexia to listen to recorded voices paired with cartoon avatars on computer screens. The subjects tried matching the voices to the correct avatars speaking English and then an unfamiliar language, Mandarin.
Nondyslexics matched voices to avatars correctly almost 70 percent of the time when the language was English and half the time when the language was Mandarin. But people with dyslexia were able to do so only half the time, whether the language was English or Mandarin. Experts not involved in the study said that was a striking disparity.
“Typically, you see big differences in reading, but there are just subtle general differences between individuals who are afflicted with dyslexia and individuals who aren’t on a wide variety of tests,” said Richard Wagner, a psychology professor at Florida State University. “This effect was really large.”
Dr. Sally Shaywitz, a director of the Center for Dyslexia and Creativity at Yale University, said the study “demonstrates the centrality of spoken language in dyslexia — that it’s not a problem in meaning, but in getting to the sounds of speech.”
That is why dyslexic children often misspeak, she said, citing two examples drawn from real life. “A child at Fenway Park watching the Red Sox said, ‘Oh, I’m thirsty. Can we go to the confession stand?,’ ” she said.
“Another person crossing a busy intersection where many people were walking said, ‘Oh, those Presbyterians should be more careful.’ It’s not a question of not knowing, but being unable to attach what you know is the meaning to the sounds.”
Dr. Gabrieli said the findings underscored a critical problem for dyslexic children learning to read: the ability of a child hearing, say, a parent or teacher speak to connect the auditory bits that make up words, called phonemes, with the sight of written words.
If a child has trouble grasping the sounds that make up language, he said, acquiring reading skills will be harder.
The research shows that spoken language deficiencies persist even when dyslexics learn to read well. The study subjects were mostly “high-functioning, high-I.Q. young adults who had overcome their reading difficulty,” Dr. Gabrieli said. “And yet when they had to distinguish voices, they were not one iota better with the English-language voices that they’ve heard all their life.”
Experts said the new study also shows the interconnectedness of the brain processes involved in reading. Many scientists had considered voice recognition to be “like recognizing melodies or things that are primarily nonverbal,” Dr. Gabrieli said. Voice recognition was thought to be a separate task in the brain from understanding language.
But this research shows that normal reading involves a “circuit, the ability to have all of those components integrated absolutely automatically,” said Maryanne Wolf, a dyslexia expert at Tufts University. “One of the great weaknesses in dyslexia is that the system is not able to integrate these phoneme-driven systems” with other aspects of language comprehension.
As a follow-up, the M.I.T. researchers have been scanning the brains of subjects performing voice recognition and other activities, and have found “very big differences in dyslexics and nondyslexics in a surprisingly broad range of tasks,” Dr. Gabrieli said. “We think there might be a broader kind of learning that’s not operating very well in these individuals and that in some areas you can circumvent it pretty well. But in language and reading, it’s hard to circumvent.”
One of the unusual aspects of the M.I.T. study is that it isolated the skill of processing vocal speech from reading and from skills involving the meaning of language, experts said. The sentences were basic, like “The boy was there when the sun rose,” and the Mandarin sounds meant nothing to the listeners.
Dr. Wagner suggested that something like the voice-recognition task might be used to identify young children at risk for dyslexia.
Often diagnostic tests require separating sounds from words. A child might be asked to say “cowboy” without the “boy” part.
“For young children, it’s a real difficult task,” Dr. Wagner said. “Sometimes they’ll say, ‘cowboy without saying boy,’ because that’s exactly what you’ve asked them. The holy grail is to come up with tasks you can give to a 3-year-old.”
Dr. Shaywitz said the study also has implications for teaching.
If a teacher asked, “ ‘Oh, Johnny, what is the capital of New York State?,’ Johnny will go, ‘Uh, uh, uh,’ and the teacher will say, ‘Oh, gee, you don’t know it,’ ” Dr. Shaywitz said. “It’s more likely to be a problem of word retrieval than knowledge. If she reframes it as, ‘Is the capital Houston or Albany?,’ Johnny is more likely to answer correctly.”