The dyslexic brain struggles to read because even small distractions can throw it off, according to a new model of dyslexia emerging from a group of recent studies.
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 and former USC graduate student Anne Sperling (now at the National Institute of Mental Health), USC psychologist Franklin Manis and University of Wisconsin, Madison psychologist Mark Seidenberg.
The most recent study is due to be published later this month in Psychological Science.
Confusion about dyslexia rivals the confusion of dyslexia. Many still think that to have dyslexia means to mix up your letters (one of many possible symptoms having to do with word recognition, directional ability and decoding of symbols).
What is known is that dyslexia affects millions of children, with estimates of its incidence ranging from 5 to 15 percent.
Sperling, who conducted her research as a doctoral student at USC, said the new findings point to a deeper problem - not just a visual deficit - affecting all areas of perception.
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.