November 2009     The vast majority of school-aged children can focus on the voice of a teacher amid the cacophony of the typical classroom thanks to a brain that automatically focuses on relevant, predictable and repeating auditory information, according to new research from Northwestern University.

But for children with developmental dyslexia, the teacher's voice may get lost in the background noise of banging lockers, whispering children, playground screams and scraping chairs, the researchers say. Their study appears in the Nov. 12 issue of Neuron.

Recent scientific studies suggest that children with developmental dyslexia -- a neurological disorder affecting reading and spelling skills in 5 to 10 percent of school aged children -- have difficulties separating relevant auditory information from competing noise.

The research from Northwestern University's Auditory Neuroscience Laboratory not only confirms those findings but presents biological evidence that children who report problems hearing speech in noise also suffer from a measurable neural impairment that adversely affects their ability to make use of regularities in the sound environment.

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 during which the brain's response to these sounds was continuously measured.

The study suggests that in addition to conventional reading and spelling based interventions, poor readers who have difficulties processing information in noisy backgrounds could benefit from the employment of relatively simple strategies, such as placing the child in front of the teacher or using wireless technologies to enhance the sound of a teacher's voice for an individual student.

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 (e.g. noise).

"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," said Nina Kraus, Hugh Knowles Professor of Communication Sciences and Neurobiology and director of the Auditory Neuroscience Laboratory.

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.

From a media release by Northwestern University, November 11, 2009 

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