THÈME DE RECHERCHE : 

Déficit visuel magnocellulaire et confusion de lettres miroirs dans la dyslexie: relation causale et implications pour la prise en charge.

Magnocellular deficiency and mirror letter confusions in dyslexia: causal relation and implications for treatment.

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SUBVENTION JED : 27.500 €

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OBJECTIF DU PROJET : 

I

An important number of children (10 — 15 %) have a specific reading disability (SRD) called “developmental dyslexia”, despite their normal intellectual abilities, socio-economic and educational opportunities. Among them, a significant number suffers from a series of visual problems. One of the most frequent of these visual problems is the confusion of mirror letters. Already during the first years of schooling, children with dyslexia present more reversals errors (e.g., confusions between p, b, d, q) than typical readers of the same age. For many of them this difficulty persists until adulthood. For this reason, reversal errors (e.g., d for b, u for n) is often considered one of the hallmark of dyslexia. The origin of these errors and how to treat them remains unknown, however.

Some general suggestions have been offered to explain this deficit. For instance, some researchers have proposed that difficulties in discriminating mirror letters could be the consequence of a “reduction coding” by which letters’ orientation would not be represented, or not sufficiently well, in the dyslexic’s visual system or of “duplication coding” by which both orientations would co-exist in the dyslexics’ visual system, possibly due to insufficient pruning of interhemispheric connections. However, these suggestions can be questioned on both logical and empirical grounds. For instance, none of these hypotheses is able to account for the fact that the dyslexics who have difficulties discriminating mirror letters, typically do not confuse the orientation of everyday life’s objects, such as the side of a cup handle. After a century of research, the origin of these errors and their relationship with dyslexia remains elusive.

The goal of this research is to address this question, which relates to fundamental issues about parallel processing in the visual system and has the potential to provide guidelines for the design of new technologies to assist reading in dyslexia. More precisely, based on exciting preliminary results from our group, this project aims at testing the hypothesis that dyslexics who make frequent letter reversals have a deficient magnocellular visual channel and, therefore, will benefit from technologies compensating this deficit by facilitating the treatment of visual information through this pathway.