A role for dyslexia in language evolution?

In a new paper Gabrieli highlight the recent results of cognitive neuroscience research on dyslexia and its potentdiial consequences for the treatment of dyslexic children through educative measures.

What Gabrieli show is that dyslexia, an impairement in reading abilities linked to difficulties in phonological processing, can be detected very early on by brain imaging techniques and treated in some cases with specific training in reading during the beginning of learning. If left undetected and untreated, dyslexia can cause prolonged difficulties in reading abilities and decrease motivation to read.

Dyslexia and its orthographic consequences could be of great interest for cognition-and-culture oriented scientists because orthographic errors generated by dyslexia or other processes produce linguistic variation at the origin of language evolution.



Dyslexia, reaching around 10% of children, could therefore be an important factor of language evolution and may orient language evolution in different ways. If some words are more difficult to write and memorize for dyslexic children because the relation between their phonological form and their written form do not concord, dyslexic children may introduce new variants that are easier to learn for them. Two possibilities may occur, new words may either be easier to learn for dyslexic children and neutral or easier to learn for non dyslexic children, in which case we expect the spread of dyslexic free variants, or it could be that the new variants are easier to learn for dyslexic children but not for normal children, in which case we expect the new variants not to spread. Because dyslexia is related to a deficit in phonological processing, it should not be a problem for non dyslexic children to learn non error inducing words, I therefore suspect the former case is the most probable and language evolve in part toward dyslexic free words.



I can see two ways in which the interactions between dyslexia and language evolution could probably be tested. One way uses language evolutionary trees to test for the progressive desapearance of dyslexic prone words. The other possibility is to look at correlation between words frequency of use and dyslexic prone words, if dyslexia has an effect on language evolution, it should be stronger for frequent words than for non frequent ones.

Here is the abstract of Gabrieli's paper:

Reading is essential in modern societies, but many children have dyslexia, a difficulty in learning to read. Dyslexia often arises from impaired phonological awareness, the auditory analysis of spoken language that relates the sounds of language to print. Behavioral remediation, especially at a young age, is effective for many, but not all, children. Neuroimaging in children with dyslexia has revealed reduced engagement of the left temporo-parietal cortex for phonological processing of print, altered white-matter connectivity, and functional plasticity associated with effective intervention. Behavioral and brain measures identify infants and young children at risk for dyslexia, and preventive intervention is often effective. A combination of evidence-based teaching practices and cognitive neuroscience measures could prevent dyslexia from occurring in the majority of children who would otherwise develop dyslexia.

Gabrieli, J. D. E. 2009 Dyslexia: A New Synergy Between Education and Cognitive Neuroscience. Science 325, 280-283.

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