A validated definition of dyslexia has been provided in a new study, which shows how otherwise bright and intelligent people struggle to read.
Contrary to popular belief, some very smart, accomplished people cannot read well. This unexpected difficulty in reading in relation to intelligence, education and professional status is called dyslexia.
And now researchers at Yale School of Medicine and University of California Davis have presented new data to explain this learning disorder.
"For the first time, we've found empirical evidence that shows the relationship between IQ and reading over time differs for typical compared to dyslexic readers," said Sally E. Shaywitz from Yale School of Medicine's Department of Paediatrics, and co-director of the newly formed Yale Center for Dyslexia and Creativity.
Using data from an ongoing 12-year study of cognitive and behavioural development in a representative sample of 445 Connecticut schoolchildren, Shaywitz and her team tested each child in reading every year and tested for IQ every other year.
They were looking for evidence to show how the dissociation between cognitive ability and reading ability might develop in children.
The researchers found that in typical readers, IQ and reading not only track together, but also influence each other over time. But in children with dyslexia, IQ and reading are not linked over time and do not influence one another. This explains why a dyslexic can be both bright and not read well.
"I've seen so many children who are struggling to read but have a high IQ. Our findings of an uncoupling between IQ and reading, and the influence of this uncoupling on the developmental trajectory of reading, provide evidence to support the concept that dyslexia is an unexpected difficulty with reading in children who otherwise have the intelligence to learn to read," Shaywitz said.
The study will be published in the January 1, 2010 issue of the journal Psychological Science.