A Rutgers University researcher has proposed a new theory linking some forms of dyslexia and speech and language impairments to a basic timing failure in the brain.
Previous research has suggested such disabilities may result from visual or sound problems, among other causes. But Paula Tallal, a co-director of the Center for Molecular and Behavioral Neuroscience at Rutgers’ Newark campus, said the problem may stem more from a basic difficulty the brain has in “detecting when signals enter the brain and how signals change over time in milliseconds.’'
Often, she said, children who have such problems need more time to decode the signals that bombard their brain.
Ms. Tallal said her findings, presented last month at a meeting of the Society of Neuroscience, have major implications for the way children are taught to read.
“The movement toward whole-language will put these children at much greater risk than a phonics program,’' she said. “They are just not going to pick it up by osmosis.’'
Research Findings
Ms. Tallal pointed to several studies, conducted over the past 20 years, that lend support to her theory. Much of that research was conducted with children who have developmental speech and language disorders that are not linked to a known cause, such as a hearing impairment. She said such disorders affect 3 percent to 10 percent of all schoolchildren and lead to dyslexia, or difficulty in learning to read, in later years.
In one such study, Ms. Tallal and her colleagues found that the speech- and language-impaired children had trouble understanding sounds that change quickly, such as “ba’’ and “da.’' However, when the researchers used computers to double the length of those sounds from 40 milliseconds to 80 milliseconds, the children were able to distinguish among the changing sounds.
Ms. Tallal said that the same timing problem occurs across sensory systems, regardless of whether the stimuli are verbal or not. It also hinders children’s physical responses to the stimuli they receive.
In another study, the results of which were presented for the first time at last month’s meeting, Ms. Tallal and three researchers at Washington University in St. Louis, Steve Peterson, Julie Fiez, and Marcus Raichle, measured the brain activity in nondisabled adults listening to rapidly changing sounds.
Using positron emission tomography, or PET, scans, the researchers found that the more complex sounds resulted in an increase in activity in the left and right temporal and frontal cortexes--areas of the brain that are thought to control language. One location was near Broca’s area, which, when damaged, is known to cause aphasia, a condition characterized by difficulty in expressing oneself.
“This suggests what is happening in front has more to do with organizing perception and production,’' she said.
Ms. Tallal and Terry Jernigan, a colleague at the Center for Molecular and Behavioral Neuroscience, also found that the areas of the brain associated with language were markedly smaller in some two dozen language-impaired 10-year-olds they studied.
The size of the temporal and frontal cortexes, they said, were correlated to the degree to which those children had problems processing rapidly changing sounds.
Working with other researchers at the center, Ms. Tallal also has found that rats have a similar system for processing sounds. Previously, she said, scientists thought human beings were unique in their ability to process sounds.
“The rat studies are important because they provide a new animal model of non-verbal processing,’' she said. “This should allow us to investigate the neurobiology of sensory processes that may be precursors to speech development.’'
Teaching Reading
Ms. Tallal said her discoveries and those of other researchers show that the “dyslexic child has quite a different brain.’'
“It’s upsetting when all the research is converging on these problems and educational policy is going in another direction,’' she said.
Rather than the whole-language approach to teaching reading, which emphasizes reading literature and learning sound-symbol connections in that context, Ms. Tallal said, speech- and language-impaired children may need a more systematic approach to phonics instruction.
One such approach, pioneered by a California speech pathologist, emphasizes teaching children how to integrate the physical movements their mouths make in speech with the sounds they hear. Through questioning and use of mirrors, children discover, for example, that they purse their lips in making a “b’’ sound.
“The thing that has confused people is that people who are making good efforts to teach phonics have thought that if a person would say a word he would have to be aware of how it sounds,’' said Patricia Lindamood, who developed the method, known as auditory discrimination. That is not true, she said, for many children.
By teaching children how sounds feel, she said, she is giving their brains another way to process the information they receive.
“What the research is showing is that when you put electrodes on a person’s brain and have them read words,’' she said, “it shows action in the same parts of the brain as if the mouth had moved to say the words.’'
