When English-speaking children with dyslexia begin to read, they face the awesome task of learning more than 1,100 ways that letters in the written language are used to symbolize the 40 sounds in the spoken language.
This may explain why there are twice as many identified dyslexics in English-speaking cultures as in countries with less complex languages, according to a study appearing today in the journal Science.
The study by an international team compared the brain scan images and reading skills of dyslexic university students in Italy, France and England.
The researchers found virtually no difference in the neurological signature for dyslexia, but there was an immense difference in how well the students learned to read their native languages.
"It is much easier for dyslexics to learn to read in languages where there is a one-to-one relationship between letters and the sounds," said Chris D. Frith, a researcher at the University College London and a co-author of the study. "In English, there are more than a thousand ways to spell the sounds."
In Italian, dyslexic students have a far easier time. The 33 sounds in Italian are spelled with only 25 letters or letter combinations. There are 32 sounds in the French language, which linguists say are written in about 250 letter combinations.
The researchers noted that identified dyslexics are rare in Italy because the language helps learning readers to quickly overcome problems caused by the disorder. To find dyslexics among Italian university students, the researcher had to conduct special tests.
Experts have estimated that between 5 percent and 15 percent of Americans have some degree of dyslexia.
Dyslexia involves a brain structure that makes it difficult for a learning reader to connect verbal sounds with the letters or symbols that "spell" that sound. Such connections are essential to learn to read. In the study, researchers found that English, French and Italian dyslexics did equally poorly in tests based on the short-term memory of verbal sounds, a key measure for the disorder. Yet the Italians were far better at reading their native language than were the English and French students.
The students were then put through a series of reading exams using positron emission tomography to measure and image blood flow in specific parts of the brain, an indication of neurological activity. All of the students had the same deficits in the left temporal lobe of the brain while performing reading tasks.
"Although Italian dyslexics read more accurately than French or English dyslexics, they showed the same degree of impairment" in the brain image, the study found.
This suggests, the researchers said, that it is the language difference alone that makes it more difficult for English-speaking dyslexics to learn how to read.
"The complexity of the English and French written languages stems from historical events that have introduced spellings from other languages, while, in comparison, Italian has remained quite pure," said Eraldo Paulesu of the University of Milan Bicocca, the lead author of the study.
In English, many words share the same letter combinations but involve different sounds when spoken. For example: mint and pint; cough and bough, and clove and love. In French, the complexity stems from different letter combinations that "spell" the same or similar sound, such as au temps (at the time) and autant (as much, or so much).
Frith said that Spanish, Finnish and Czech are "dyslexia friendly" languages because they lack the sound-spelling complexity of English and French. Japanese, he said, is also easier for children.
"One study found an Australian boy in Japan who was dyslexic in English, but not in Japanese," said Frith. "That is the sort of thing that you would expect" if language was a significant factor in the severity of the reading disorder.