Codage de l'identité et de la position lors du traitement de séquences de lettres : normo-lecteur versus dyslexique. Etude comportementale chez l'enfant et étude en IRMf chez l'adulte

L'acte de lire représente une activité devenue parfaitement automatique et constitue un outil permettant de s'inscrire et de participer au monde social et culturel qui nous entoure. L'acquisition de la lecture requiert un apprentissage long et laborieux. Il repose sur la capacité des lecteurs à identifier correctement des stimuli visuels complexes à un degré tel qu'ils doivent pouvoir distinguer " lion " et " loin " ou " foin " en une seule et unique fixation. Par conséquent, le codage de l'identité et de la position de la lettre est crucial dans l'identification visuelle des mots. Ce travail de thèse s'inscrit dans ce cadre de recherche et présente deux objectifs principaux. Premièrement, nous voulions explorer la façon dont le codage de l'identité et la position de la lettre est modulé par le contexte orthographique au cours de l'acquisition de la lecture et dans le cadre de la dyslexie de développement. Les participants réalisaient une tâche de comparaison de séquences de lettres dans laquelle ils devaient juger si deux suites de lettres présentées successivement et brièvement étaient identiques ou différentes. L'identité et la position des lettres étaient manipulées par le biais d'une substitution ou d'une transposition de deux lettres au sein de la séquence. Des non-mots, des pseudo-mots et des mots ont été utilisés comme stimuli pour étudier les effets lexicaux et sub-lexicaux sur l'encodage des lettres. Les résultats montrent que le traitement orthographique (codage de l'identité et de la position des lettres) et la représentation lexicale sont soumis à des changements développementaux et sont altérés chez les enfants dyslexiques. Un trouble de l'empan visuo-attentionnel (VA), i.e. une capacité VA réduite, chez ces enfants dyslexiques permet de rendre compte de ces perturbations. Deuxièmement, nous voulions explorer, en utilisant l'IRMf, les substrats neurobiologiques du codage de l'identité et de la position des lettres en contexte non-mot chez des adultes normo-lecteurs et dyslexiques. Les normo-lecteurs montrent une forte activation dans les régions pariétales et l'aire occipito-temporale ventrale (VOT) en condition de substitution de lettres, tandis que ces activations sont absentes chez les dyslexiques. Chez les normo-lecteurs, la condition de transposition de lettres active un réseau cortical plus limité, incluant l'aire VOT, laquelle n'est pas activée chez les participants dyslexiques. Ces résultats conduisent à mieux le rôle des régions pariétales et VOT dans la phase précoce du traitement visuel des mots en lecture et dans le cadre de la dyslexie développementale.With time and practice, reading becomes a fully automatized activity that acts as an essential tool for our insertion in the social and cultural world around us. The acquisition of reading is long and laborious and relies on the readers' capacity to properly identify complex visual stimuli at such a fine degree that 'causal' must be discriminated from 'casual' within a single fixation. Consequently, letter-identity and letter-position encoding are crucial for visual identification of words. This thesis work fits into this research framework and investigates two main issues. First, we aimed to explore how letter-identity and letter-position encoding are modulated by letter context during reading acquisition and in developmental dyslexia. A letter-string comparison task was administered to participants who had to judge whether two successively and briefly presented letter strings were identical or different. Letter-position and letter-identity were manipulated through the transposition or substitution of two letters. Non-words, pseudo-words, and words were used as stimuli to investigate sub-lexical and lexical effects on letter encoding. Results show that orthographic processing (letter-identity and letter-position encoding) and lexical representations are subject to developmental changes and are strongly impaired in dyslexic children. A disorder of visuo-attention (VA) span, i.e. a reduced VA capacity, in these dyslexic children might account for this deficit. Secondly, using fMRI, we investigated the neurobiological substrates of letter-position and letter-identity encoding in non-word context in normal and dyslexic adults. Healthy readers activate the parietal and ventral occipito-temporal (VOT) areas in the substitution condition, while dyslexics do not. In healthy readers, the transposition condition activates a more limited cortical network including VOT area, which was not activated in dyslexic participants. These findings provide new insights on the role of parietal and VOT regions in the early phase of visual word processing in reading and developmental dyslexia

L'orthographe grammaticale au collège: une approche sociodifférenciée.

National audienceCette étude vise à préciser les difficultés en orthographe grammaticale de collégiens de 6e scolarisés en réseaux de réussite scolaire (RRS). Un texte de 64 mots a été dicté à 341 élèves dans trois collèges sociodifférenciés, permettant d'évaluer le marquage de l'accord en nombre (singulier, pluriel) du verbe avec le sujet, et du nom et de l'adjectif dans le groupe nominal. Les résultats montrent la fragilité du marquage du pluriel pour tous les élèves, quelle que soit la catégorie grammaticale, et cette difficulté est beaucoup plus grande dans le collège le moins favorisé

Dynamic information about letter production influences visual letter perception: <br />Evidence from an acquired letter recognition deficit

Letter recognition is traditionally assumed to involve matching a perceptual representation of a stimulus letter with a stored representation of a static letter shape. However, people learn not only to recognize letters, but also to write them, and several researchers have suggested that knowledge concerning the dynamics of letter production (e.g., knowledge about the direction and sequencing of writing strokes) may play a role in letter recognition (James & Atwood, 2009; Longcamp, Lagarrigue, & Velay, 2010; Parkinson & Khurana, 2007). We report results from NGN, a 77-year-old man who suffered a large left ventro-medial lesion as a consequence of stroke. NGN is severely impaired in visual letter identification. His perception of letter shapes is intact, but his ability to map these shapes onto abstract letter representations is severely disrupted. We investigated whether dynamic presentation of letters might improve NGN’s letter identification. Upper-case letters were presented individually in dynamic or static conditions (see Figure 1). In the Dynamic-Forward condition a moving dot drew a path from the beginning to the end of the letter as it is typically written, until the entire letter was displayed. In the Static condition the whole letter was displayed for the full duration required to “write” the letter in the dynamic condition. NGN’s letter identification accuracy was significantly higher in the Dynamic-Forward condition (90%) than in the Static condition (73%), p < .001. Two additional dynamic conditions established that the advantage of the Dynamic-Forward condition was not due to the mere presence of motion in this condition (a possibility suggested by the findings of Rauschecker et al., 2011), or to the fact that the stimulus shape evolved over time. In the Dynamic-Backward condition a moving dot “wrote” the letter from end to beginning; and in the Dynamic-Random condition the dots making up the letter shape appeared in random order at the same rate as in the other dynamic conditions, until the entire letter was displayed. In both of these conditions, NGN’s performance was significantly worse than in the Dynamic-Forward condition (ps < .01), and no better than his performance in the Static condition: Accuracy was 80% in the Dynamic-Backward condition and 74% in the Dynamic-Random condition. These results demonstrate that mere motion, or mere change over time, are not sufficient to facilitate NGN’s letter identification; only the typical writing motion is helpful. Our findings are consistent with hypotheses holding that knowledge of writing motions contributes to letter identification, and also suggest that dynamic letter displays may be worth exploring for purposes of rehabilitation. Our results also raise an interesting point about rehabilitation strategies in which individuals with letter identification deficits are asked to trace the shapes of visually-presented letters on their hands, in the air, or on a surface. Facilitatory effects of the tracing strategies on letter identification performance have typically been attributed to the tactile or kinesthetic representations activated by tracing (e.g., Starrfelt, Olafsdóttir, & Arendt, 2013). Our results suggest that the dynamic visual information provided by the tracing motions may also play an important role

Prevalence of phonological, RAN and VA span deficits in 6th grade poor readers

International audienc

Prevalence of phonological, RAN and VA span deficits in 6th grade poor readers

International audienc

Codage de l'identité et de la position lors du traitement de séquences de lettres (normo-lecteur versus dyslexique)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Heterogeneous cognitive profiles of 6th grade poor readers

International audienc

Varieties of Cognitive Profiles in Poor Readers: Evidence for a VAS-Impaired Subtype

International audienceA wide share of secondary school children does not reach the expected competence level in reading. These children could benefit from more efficient intervention responses, providing a better understanding of their cognitive weaknesses/deficits. Our aim was to explore the cognitive heterogeneity of a population of poor readers identified from a large sample of 948 sixth-grade children. We first assessed the contribution of phoneme awareness (PA), rapid automatized naming (RAN), and visual attention span (VAS) to reading performance in a subset of 281 children including poor and average readers/spellers. We show that all three skills are unique and significant predictors of reading fluency. We then restricted the analysis to participants with normal Raven’s score (IQ) and oral language skills to focus on 110 children with more specific reading difficulties. A unique VAS deficit was found in 18% of these poor readers while 20% and 15.5% showed a unique PA or RAN deficit. Children with multiple or no deficit were further identified. The overall findings provide evidence for a variety of cognitive profiles in poor readers. They suggest that, in addition to PA interventions, training programs targeting VAS might be useful for the nontrivial share of poor readers who exhibit a VAS deficit

The phonological and visual basis of developmental dyslexia in Brazilian Portuguese reading children

Evidence from opaque languages suggests that visual attention processing abilities in addition to phonological skills may act as cognitive underpinnings of developmental dyslexia. We explored the role of these two cognitive abilities on reading fluency in Brazilian Portuguese, a more transparent orthography than French or English. Sixty-six children with developmental dyslexia and normal Brazilian Portuguese children participated. They were administered three tasks of phonological skills (phoneme identification, phoneme, and syllable blending) and three visual tasks (a letter global report task and two non-verbal tasks of visual closure and visual constancy). Results show that Brazilian Portuguese children with developmental dyslexia are impaired not only in phonological processing but further in visual processing. The phonological and visual processing abilities significantly and independently contribute to reading fluency in the whole population. Last, different cognitively homogeneous subtypes can be identified in the Brazilian Portuguese population of children with developmental dyslexia. Two subsets of children with developmental dyslexia were identified as having a single cognitive disorder, phonological or visual; another group exhibited a double deficit and a few children showed no visual or phonological disorder. Thus the current findings extend previous data from more opaque orthographies as French and English, in showing the importance of investigating visual processing skills in addition to phonological skills in children with developmental dyslexia whatever their language orthography transparency

A visual processing but no phonological disorder in a child with mixed dyslexia.

International audienceThe case study of Martial, a French 9-year-old boy, who exhibits severe mixed dyslexia and surface dysgraphia is reported. Despite very poor pseudo-word reading, Martial has preserved phonological processing skills as his good oral language, good phoneme awareness and good verbal short-term memory show. He exhibited a strong length effect when reading briefly presented words but no sign of mini-neglect. His letter-string processing abilities were assessed through tasks of whole and partial report. In whole report, Martial could only name a few letters from briefly displayed 5-consonant strings. He showed an initial-position advantage and a sharper than expected left-to-right gradient of performance. He performed better when asked to report a single cued letter within the string but then showed an atypical right-side advantage. The same rightward attentional bias was observed in whole report when top-down control was prevented. Otherwise, Martial showed preserved single letter identification skills and good processing of 5-letter strings when letters were sequentially displayed one at a time. His poor letter-string processing thus reflects a parallel visual processing disorder that is compatible with either a visual attention (VA) span or a visual short-term memory disorder. Martial was further engaged in a complex reaching movement task involving VA and simultaneous processing. He performed motor sequences not as a whole but as a succession of independent motor units, suggesting that his attention was not allocated in parallel to the two to-be-reached targets prior to movement execution. Against a more basic motor disorder however, he showed good performance in a task of cyclical pointing movements. The overall findings suggest that Martial suffers from a visual simultaneous processing disorder that disturbs letter identification in strings. Instead of being restricted to letter-string processing, this VA disorder might extend to non-verbal task