Reading may seem like a visual skill, but according to new research on dyslexia, children who excel at reading tend to be all ears.
Their brains process the sounds of speech in a more consistent way than those who struggle to read, scientists at Northwestern University in Chicago have found.
In a study published in February in the Journal of Neuroscience, researchers recorded the brainwaves of 100 children with normal hearing, aged six to 13. Using scalp electrodes, they measured the children's neural responses as they listened to the syllables "ba" and "ga."
The brainwaves of dyslexic children showed erratic patterns, indicating the children had difficulty encoding the sounds, said the study's co-author, Nina Kraus, a professor of neurobiology, physiology and communication at Northwestern University.
This deficit in the brain's ability to recall speech sounds "may be a biological marker of dyslexia," she said.
Although many different factors may contribute to dyslexia, the link between a child's reading ability and auditory processing skills appears to be a "highly significant relationship," said Kraus.
Reading involves an internal hearing of printed language, Kraus explained. As children learn to read, they begin to hear the sounds of consonants, vowels and syllables in their heads and make meaningful connections between sounds and information.
One in 10 people has dyslexia. The reading disability does not affect intelligence, but it does interfere with the ability to recognize words, understand the meaning of a sentence and make sense of written language.
Children with dyslexia may not make strong sound-to-meaning connections in language because of how their nervous systems are set up, Kraus said.
Distinguishing between consonants is particularly difficult for people with dyslexia, she said. Consonants are spoken quickly, compared to the sound of vowels, yet they carry the meaning of words such as "bat" and "cat," she pointed out. "The acoustics are tricky."
Moreover, previous studies by Kraus and other researchers suggest that children with dyslexia are less likely to tune out irrelevant speech sounds, leading to difficulty in perception and ultimately in reading.
The good news is that children's brains are particularly malleable.
In an earlier study, Kraus and colleagues monitored dyslexic children who wore a listening device for one year. The device heightened the children's ability to hear their teacher's voice amid the cacophony of the classroom. By the end of the study period, the children's reading ability had improved and their brainwave responses to speech sounds resembled those of good readers.
"They learned which aspects of sound really did carry meaning," Kraus said.
Her lab is now studying how music lessons could help children with reading difficulties. The research team is partway through a four-year study of brain development in Chicago-area high school students who receive music training.
Music fine-tunes auditory skills involved in identifying pitch, timing and timbre (the difference, for example, between the sound of a tuba and violin). In multiple studies, Kraus and colleagues have demonstrated that compared to non-musicians, adults with music training are better able to track the pitch, timing and timbre of music as well as speech, and are more likely to exclude unimportant sounds.
"There really is a connection between music and reading," Kraus said.
Although young brains are easier to rewire, research suggests that older adults can also improve their auditory processing skills. In a study of 70 adults with an average age of 63, Kraus and colleagues found that those who used Posit Science's "Brain Fitness" software for 40 hours over eight weeks were able to pick out 40-per-cent more words from background noise compared to adults who had watched educational videos. "We saw a partial reversal in age-related hearing loss," Kraus said.
(The study, published in February in the Proceedings of the National Academy of Sciences, had no financial connection to the software company.)
Computer-based reading tools for improving auditory processing skills in children are already on the market, such as Fast ForWord by Scientific Learning, a company based in Oakland, Calif.
Ideally, however, children at risk for dyslexia would receive help before facing the frustration of learning to read. To that end, Kraus and colleagues are in the first year of a five-year study to identify biomarkers of reading impairment in preschool children. They are tracking their neural responses to speech sounds, ability to rhyme and other measures of language development.
Except in cases of hearing impairment, reading and communication problems in people of all ages are "a rather consistent story," she said. "It all involves sound processing in the brain and making sound-to-meaning relationships."