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According to a hypothesis published in Nature Neuroscience, the brain of dyslexic individuals may have a general problem forming perceptual categories, including the templates for printed letters and speech sounds. Research scientists evaluated signal-noise discrimination in children with and without dyslexia, using magnocellular and parvocellular visual stimuli presented either with or without high noise. Dyslexic children had elevated contrast thresholds when stimuli of either type were presented in high noise, but performed as well as non-dyslexic children when either type was displayed without noise. 
These findings suggest that deficits in noise exclusion, not magnocellular processing, contribute to the etiology of dyslexia. With noise, the dyslexic children needed more brightness contrast to perform the same tasks as their non-dyslexic peers. This was true whether the patterns required fast or slow processing.
Children with dyslexia have a hard time focusing in on what is relevant and ignoring what is irrelevant. Parents and teachers of dyslexic children know this, however, this study reinforces that utilizing a method that helps children to concentrate on a reading task and excludes distractions should be helpful. Specifically, programs that help children form sharper perceptual categories for sounds and letters could supplement existing dyslexia interventions.
This research adds to the body of knowledge about this learning disability and provides an explanation for why a child is failing to read and helps to explain why certain methods are effective. It does not support the idea that children need special glasses or visual training or anything specifically related to treating their vision.
Nature Neuroscience Abstract
Current PubMed Review of Dyslexia and Visual Processing
Dyslexia Information Page
Learning Disabilities Association of America
International Dyslexia Association
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