Fabrice Robichon

Developmental Dyslexia: Re-Evaluation of the Corpus callosum in Male Adults

Using a new method based upon the measurement of four angles, we analyzed the corpus callosum of 23 adult male dyslexics and 25 age-matched controls on MRI sagittal scans. Two out of the four angles measured showed significant differences between the groups that are consistent with previous findings concerning the size of the corpus callosum in dyslexics. In particular, posterior regions are concerned, displaying a lowered corpus callosum in dyslexics. These findings are discussed in relation to cortical parietal asymmetries and possible hormonal events, referring to the testosterone hypothesis, that could occur in utero or in the perinatal period in the dyslexic population.

Static postural control in children with developmental dyslexia

The present investigation tries to better understand potential association and causal relationship between phonological and postural impairment due to developmental dyslexia. The study included 50 boys with developmental dyslexia and selected on the basis of their overall reading difficulties, and 42 control boys. Body sway during a quite standing posture eye open and eye closed on a force platform were tested in the two groups of subjects that were between 10 and 13 years of age. Analysis of classical parameters quantifying the centre of pressure (CP) displacements along antero-posterior and lateral axes showed a significant difference between the two groups. Dyslexic children showed on average greater instability, with greater length, variability and mean power frequency of CP displacements with or without vision. Our results demonstrate that postural parameters may discriminate between children with dyslexia and age-equivalent controls.

The development of perceptual sensitivity to second-order facial relations in children.

This study investigated childrens perceptual ability to process second-order facial relations. In total, 78 children in three age groups (7, 9, and 11 years) and 28 adults were asked to say whether the eyes were the same distance apart in two side-by-side faces. The two faces were similar on all points except the space between the eyes, which was either the same or different, with various degrees of difference. The results showed that the smallest eye spacing children were able to discriminate decreased with age. This ability was sensitive to face orientation (upright or upside-down), and this inversion effect increased with age. It is concluded here that, despite early sensitivity to configural/holistic information, the perceptual ability to process second-order relations in faces improves with age and constrains the development of the face recognition ability.

An electrophysiological study of dyslexic and control adults in a sentence reading task.

Event-related potentials and cued-recall performance were used to compare dyslexic and control adult subjects. Sentences that ended either congruously or incongruously were presented visually, one word at a time, at fast (stimulus-onset-asynchrony (SOA)=100 ms) or slow (SOA=700 ms) rates of presentation. Results revealed (1) a large effect of presentation rate that started with the N1-P2 components and lasted for the entire recording period, (2) larger N400 components for dyslexic than control subjects, at slow presentation rates, to both congruous and incongruous endings and (3) a large ERPs difference related to memory (Dm effect) that did not differentiate controls from dyslexics but was larger at slow than at fast rates of presentation. These findings indicate that the reading impairment observed in the present group of adult dyslexics is more likely to result from difficulties integrating the meaning of words within a sentence context than from pure sensory processing deficits.

Proprioception oculaire et dyslexie de développement : À propos de 60 observations cliniques

But de l’etude L’objectif de ce travail est d’evaluer la presence d’anomalies de la proprioception constituant le syndrome de deficience posturale au sein d’une population d’enfants atteints de dyslexie de developpement. Patients et methodes Soixante patients de sexe masculin, âges en moyenne de 11 ans et 9 mois, ont ete inclus dans l’etude. Le diagnostic de dyslexie de developpement a ete confirme par un examen neuropsychologique a l’aide d’epreuves standardisees. Apres un interrogatoire visant a rechercher les signes fonctionnels evocateurs d’une anomalie proprioceptive, les patients ont fait l’objet d’un examen clinique ophtalmologique et postural en 9 etapes precisement decrites. Resultats La totalite des patients recrutes pour l’etude presentait des signes cliniques permettant de confirmer l’existence d’un trouble de la proprioception entrant dans le cadre du syndrome de deficience posturale. Conclusion Cette etude ouvre une nouvelle voie de recherche concernant l’origine et le traitement de la dyslexie de developpement.PURPOSE The objective of this study is to assess proprioception anomalies in postural deficiency syndrome in a group of children suffering from reading impairment. MATERIAL AND METHODS Sixty male patients with an average age of 11 years and 9 months were included in the study. Initially, they were given a standardized neuropsychological examination, which confirmed the diagnosis of reading impairment. Then after filling out a questionnaire seeking a proprioceptive anomaly, the patients were subjected to a clinical ocular and postural examination consisting of nine precisely described steps. RESULTS All of the patients recruited for the study presented clinical signs confirming a proprioception disorder found as a part of postural deficiency syndrome. CONCLUSION This study opens a new direction for research concerning the origin and treatment of at least some reading-impaired children.

A linguistic dissociation in Williams syndrome: Good at gender agreement but poor at lexical retrieval

Williams syndrome (WS) is a rareneuro-developmental disorder characterised byspared language in the face of serious deficitsin nonlinguistic cognitive abilities. Weconducted a study on ten WS individuals inwhich gender agreement and gender assignmentwere assessed by means of two tasks: gendercategorisation and gender concord. Subjectsperformed gender categorisation to real nounswhose gender was regular or exceptional giventheir ending, and to invented nouns which werecomposed of nonword or word stems and realword-endings. The same material was used in thegender concord task in which subjects had tomatch the items with the appropriate form ofthe article and the adjective carrying genderagreement. In the gender categorisation of realwords, WS were lower than controls but bothgroups demonstrated a similar sensitivity togender-ending regularities. In the gendercategorisation of nonwords, the results showeda clear dissociation. The WS subjects producedmore ending-consistent responses than thecontrols. Contrary to the controls, WS reliedheavily on the gender clue provided by theending even when the gender of the word evokedby the stem of the invented word was opposed tothat evoked by the ending. Participants with WSwere not influenced by the specific word evokedby the stem of the invented word. In the secondtask (concord task), the WS subjects performed well although lower than thecontrols. We concluded that the WS people werenot impaired in gender agreement which relieson syntactic rules and/or on the extraction ofregularities but experienced difficulties inretrieving lexical instances.

Étude de l’impact du contrôle postural associé au port de verres prismatiques dans la réduction des troubles cognitifs chez le dyslexique de développement

But de l’etude L’objectif de ce travail est d’evaluer l’impact des modifications proprioceptives induites par un traitement postural sur les troubles cognitifs d’une population d’enfants souffrant de dyslexie de developpement. Patients et methodes Il a ete constitue un groupe de 20 enfants dyslexiques traites par prismes posturaux, semelles « de posture » et reeducation posturale, et un groupe temoin de 13 enfants dyslexiques portant uniquement des lunettes sans prismes. Tous les enfants etaient de sexe masculin. Lors de leur inclusion dans l’etude (M0) et 6 mois plus tard (M6), tous les participants ont ete evalues par un bilan ophtalmologique et postural et ont recu un examen neuropsychologique concernant les processus visuo-lexicaux par un examinateur en insu ainsi que les processus phonologiques et metaphonologiques. Resultats L’âge moyen des enfants du « groupe traite » etait de 11 ans et 5 mois et celui des enfants du « groupe non traite » de 11 ans et 7 mois. Quatre enfants du « groupe traite » ont ete exclus a M6 pour non-observance du traitement. Tous les patients dyslexiques presentaient un syndrome de deficience posturale lors de l’inclusion. Chez les sujets traites, le traitement a ete benefique pour les signes fonctionnels et la plupart des signes physiques par rapport au « groupe non traite ». Chez 13 des 16 enfants traites, il a ameliore de maniere significative certains parametres de la dyslexie, notamment le test de leximetrie globale, la lecture des mots reguliers et irreguliers, et les epreuves de decision orthographique et de completion graphemique. Les epreuves concernant les processus phonologiques et celles concernant la manipulation mentale des sons du langage (conscience phonologique) n’ont pas ete significativement ameliorees. Conclusion Les resultats de cette etude ouvrent une nouvelle voie de recherche en montrant qu’une modification de la proprioception peut etre benefique sur certains elements cliniques rencontres dans la dyslexie de developpement. Le niveau d’action du traitement postural sur les signes de dyslexie qui se sont ameliores reste a preciser. Cette etude preliminaire doit etre completee par un essai therapeutique sur un plus grand nombre de patients et pendant une plus longue duree.