NORTHWESTERN (US)—Children with developmental dyslexia could benefit from the use of simple strategies, such as sitting in front of the teacher or using wireless technologies to enhance the sound of a teacher’s voice.
These children not only have problems hearing speech in noise, but also suffer from a measurable neural impairment that adversely affects their ability to make use of regularities in the sound environment, a study from Northwestern University finds.
Between 5 and 10 percent of school-age children suffer from dyslexia.
“The ability to sharpen or fine-tune repeating elements is crucial to hearing speech in noise because it allows for superior ‘tagging’ of voice pitch, an important cue in picking out a particular voice within background noise,” says Nina Kraus, Hugh Knowles Professor of Communication Sciences and Neurobiology and director of the Auditory Neuroscience Laboratory at Northwestern University.
In the study, which appears in the Nov. 12 issue of Neuron, Kraus and her team demonstrate that the remarkable ability of the brain to tune into relevant aspects in the soundscape is carried out by an adaptive auditory system that continuously changes its activity based on the demands of context.
Good and poor readers were asked to watch a video while the speech sound “da” was presented to them through an earphone in two different sessions while the brain’s response to the sounds was continuously measured.
In the first session, “da” was repeated over and over and over again (in what the researchers call a repetitive context). In the second, “da” was presented randomly amid other speech sounds (in what the researchers call a variable context).
In an additional session, the researchers performed behavioral tests in which the children were asked to repeat sentences that were presented to them amid increasing degrees of noise.
“Even though the children’s attention was focused on a movie, the auditory system of the good readers ‘tuned in’ to the repeatedly presented speech sound context and sharpened the sound’s encoding.
In contrast, poor readers did not show an improvement in encoding with repetition,” says Bharath Chandrasekaran, lead author of the study. “We also found that children who had an adaptive auditory system performed better on the behavioral tests that required them to perceive speech in noisy backgrounds.”
Interestingly, the researchers found that dyslexic children showed enhanced brain activity in the variable condition. This may enable dyslexic children to represent their sensory environment in a broader and arguably more creative manner, although at the cost of the ability to exclude irrelevant signals.
“The study brings us closer to understanding sensory processing in children who experience difficulty excluding irrelevant noise. It provides an objective index that can help in the assessment of children with reading problems,” Kraus says.
For nearly two decades, Kraus has been trying to determine why some children with good hearing have difficulties learning to read and spell while others do not.
Early in her work, because the deficits she was exploring related to the complex processes of reading and writing, Kraus studied how the cortex—the part of the brain responsible for thinking—encoded sounds. She and her colleagues now understand that problems associated with the encoding of sound also can occur in lower perceptual structures.
The study was supported by the National Institutes of Health and the National Science Foundation.
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