In the past couple of decades, scientists have learned a great deal about the neurological causes of dyslexia. But what they hadn't yet explained is why its incidence varies so from country to country--and what that difference means. Last week, Italian, French and British researchers proposed an answer. The variability, they wrote in Science, depends greatly on the complexity of writing systems. The team offered what it described as the first compelling evidence that the disorder has a common neurological basis across linguistic and cultural boundaries.
The findings mesh perfectly with what we already know about how the brain reads, says Dr. Bennett Shaywitz, who co-directs the Center for the Study of Learning and Attention at Yale University. The brain, he explains, does not have an innate reading ability--as it does for speech--so it deals with the written word by converting it into the nuts and bolts of a familiar phonetic language. According to prevailing theory, the reading centers of the brain break words down into sound units known as phonemes and recognize them as the elements of a phonetic code. Then the centers assemble that code to derive meaning from the symbols on the page. Most of us learn to do this seamlessly by the time we're seven years old.
Dyslexics, however, often can't get past the first step--breaking written words down into phonemes. This in no way reflects on their intelligence. Artist Robert Rauschenberg, actor Tom Cruise and Kinko's founder Paul Orfalea are just three of countless famous and successful dyslexics. Historical figures who may have had the disorder include the poet W.B. Yeats and Leonardo da Vinci. Nonetheless, it can be a lifelong challenge.
In their study, the scientists compared the reading ability of dyslexics from Britain, France and Italy and found that Italian dyslexics read far better than their French and English counterparts. Brain scans conducted during reading exercises confirmed that the boundary between language and visual processing areas was inactive in dyslexics, no matter what language they spoke. So why do Italian dyslexics read better? "The difference is not in the languages themselves," says lead author Eraldo Paulesu of the University of Milan Bicocca. "It's in their writing systems, which vary in complexity for historical reasons."
English has 1,120 different ways of spelling its 40 phonemes, the sounds required to pronounce all its words. By contrast, Italian needs only 33 combinations of letters to spell out its 25 phonemes. As a result, reading Italian takes a lot less effort, and that's probably why the reported rate of dyslexia in Italy is barely half that in the U.S., where about 15% of the population is affected to varying degrees. By some estimates, Americans spend more than $1 billion a year to help their kids cope with dyslexia. Many Italian dyslexics, on the other hand, aren't even aware they have a problem--and would notice it only if given a battery of psychological tests.
Explaining this discrepancy isn't all that the study has accomplished. By helping establish a universal neurological basis for dyslexia, the scientists make it clear that teachers ought to think twice before they dismiss the reality of a child's dyslexia. This, sad to say, still happens all too often more than a century after the disorder was first identified.