Dyslexia is increasingly believed to be a disorder that has a genetic and biological origin; a deficit in phonological (language sound) processing is thought to be the causal link between brain abnormality and reading difficulties. However, it is an established fact that countries that have a more complex or irregular system of writing, or orthography, have a higher incidence of dyslexia, for example, a study of the prevalence of dyslexia in 10-year-old children in Italy was found to be half that of the USA.
Why is this? Do the brains of dyslexics across different languages have different processing problems?
Now, by studying adult dyslexics across three language groups--French, Italian, and English--an International research team, directed by Professor Eraldo Paulesu, University of Milan Bicocca, has found that this is not the case.
The results of their research, published in the 16th March issue of Science, show for the first time that the neurological basis for dyslexia is the same across French, English and Italian languages, but that the disorder manifests itself in different ways according to the regularity of the orthography.
English and French are both languages that are said to have an irregular orthography. In English, there are 1,120 ways of representing 40 sounds (phonemes) using different letter combinations (graphemes). Mapping letters to word sounds is ambiguous; this is illustrated by pairs of words such as mint/pint, cough/bough, clove/love, where you can only read each pair correctly if you have previously learnt how they should sound. By contrast, in Italian there is no such ambiguity and 33 graphemes are sufficient to represent the 25 phonemes. This means that the same letter groups in Italian almost always represent the same unique sound, which makes the written language logical and easy to read.
Senior author, Professor Uta Frith, Institute of Cognitive Neuroscience, University College London, commented: "This research proves the existence of a universal neurological basis for dyslexia. It also highlights the impact that the complexity of orthography can have on reading proficiency of dyslexics and therefore the severity of the disease and the ease of diagnosis. This means that in the Italian population there may be hidden cases of dyslexia. On the other hand, otherwise mild cases of dyslexia may appear far worse in irregular orthographies like that of English or French."
The researchers showed that French, English and Italian dyslexics all did equally poorly in tests that involved phonological short-term memory, whereas Italian dyslexics performed better in reading tests, in particular achieving fewer errors than their English and French counterparts. In order to determine if this disparity had a neurological basis, the researchers used positron emission tomography (PET) to visualise regional cerebral blood flow, and hence neural activity, resulting from exposure to printed material. Their results prove that French, English, and Italian dyslexics have the same difficulties in carrying out phonological processing tasks and reduced activation of the left temporal lobe during reading tasks.
"It is important to make the distinction between orthography and language," commented Professor Paulesu. "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. The addition of the data from the French subjects reinforces findings that languages with complex orthographies are difficult for both dyslexics and non-dyslexics to read. There is an argument for reforming complex orthographies to improve literacy problems in these languages as attempted by the U.S. Webster reform, which simplified the spelling of groups of words according to sets of rules; an example is the change of colour to color."
This research was funded by the Gatsby Foundation, the Wellcome Trust and the U.K. Medical Research Council.
1. The Webster Reform -- In 1864, the U.S. Government officially implemented parts of the Webster Reform for the simplification of English language.
2. The irregularity of the French language stems not from the same letter combinations resulting in different sounds (as with English), but rather from the number of letter combinations that can represent the same sound. Consider the similarity in pronunciation between au temps and autant.
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