The studies contradict an influential, 30-year-old theory that blamed dyslexia on a neural deficit in processing the fast sounds of language. Instead, the studies suggest that children with dyslexia have bad filters for irrelevant data. As a result, they struggle to form solid mental categories for identifying letters and word sounds.
Such children may benefit from intensive training under "noisy" conditions to strengthen their mental templates, said University of Southern California neuroscientist Zhong-Lin Lu. Lu was a co-author on three studies, along with lead author Anne Sperling from the National Institute of Mental Health.What is known is that dyslexia affects millions of children, with estimates of its incidence ranging from 5 to 15 percent.
Sperling said people with dyslexia appear to have shaky mental categories for the essential sounds that make up language. "It's harder to make a [language] task automatic when your categories are fuzzier than they ought to be to begin with," she said. "In terms of treatment, the results suggest that programs that foster the development of sharper perceptual categories for letters and letter sounds might be a good way to supplement existing dyslexia interventions," she added. Lu said, "Train them in noise."
Johannes Ziegler of the Universite de Provence in Marseille, France, was the lead author on a study of dyslexia and auditory noise. Ziegler said his results suggest that dyslexia stems from shaky categories for phonemes (the basic sounds of language). "In silence, information is often redundant and dyslexics get away with the perception deficit," Ziegler said. "In noise, however, they can no longer compensate. "What is important is that noisy environments are the rule and not the exception," he added, citing a study from South Bank University in the U.K. that found average noise levels in primary classrooms to be as high as near a busy intersection.
MEDICA.de; Source: University of Southern California