La lecture et l’écriture sont deux activités complexes qui contribuent à la réussite dans toutes les disciplines scolaires. Pour l’apprenti scripteur, et plus particulièrement pour l’élève qui éprouve des difficultés d’apprentissage (notamment l’élève dyslexique), l’apprentissage de l’orthographe représente un réel défi et nécessite souvent des années d’effort. Or, la connaissance du code orthographique constitue le socle sur lequel se construit la compétence orthographique. La reconnaissance et la production de mots écrits impliquent la mise en place d’un noyau de connaissances communes se rapportant aux connaissances orthographiques, c’est-à-dire aux connaissances rattachées aux propriétés phonologiques, morphologiques et visuelles du code orthographique. Ainsi, tout au long du développement de la compétence orthographique, le lecteur-scripteur doit notamment construire des représentations orthographiques de plus en plus stables et mieux définies qui tiennent compte de l’ensemble des propriétés du code orthographique. Des données empiriques récentes indiquent toutefois que les élèves dyslexiques, qui commettent davantage d’erreurs orthographiques de fusion et de segmentation de mots que les élèves sans difficulté à l’écrit, ne semblent pas disposer de représentations orthographiques précises des mots à orthographier, et plus spécifiquement de bonnes représentations du début et de la fin des mots. L’objectif général de cette étude est donc d’expliquer les erreurs orthographiques de frontières lexicales chez les élèves dyslexiques. Comme à notre connaissance, il n’existe pas de norme quant au développement des connaissances des frontières lexicales chez les élèves normo-lecteurs/scripteurs, le premier objectif spécifique est de décrire, de façon transversale et longitudinale, les performances d’élèves normo-lecteurs/scripteurs de la maternelle à la 4e année du primaire à des épreuves évaluant les connaissances des frontières lexicales (étude 1). La mise en place de cette référence développementale a permis de répondre au deuxième objectif spécifique qui est d’évaluer les connaissances des frontières lexicales d’élèves dyslexiques du primaire (étude 2). Pour évaluer les compétences en lecture et en production de mots, une épreuve de lecture de la batterie de tests du K-ABC et une dictée de mots insérés en contexte phrastique ont été proposées. Trois épreuves (décision lexicale, identification lexicale et permutation lexicale), variant en termes de degré de contraintes cognitives, ont été effectuées par tous les participants à l’oral et à l’écrit afin d’évaluer leurs connaissances des frontières lexicales. / Reading and writing are two complex activities that contribute to success in all school subjects. For apprentice writers, and particularly for students with learning difficulties (notably students with dyslexia), learning to spell represents a real challenge and often requires years of effort. To be successful, students require knowledge of the orthographic code, which is the foundation upon which spelling ability it built. To recognize and produce written words, students must develop a set of core skills that are linked to orthographic knowledge, including knowledge of the phonological, morphological and visual properties of the orthographic code. As their spelling skills develop, readers and writers must construct increasingly stable and better defined orthographic representations that reflect the properties of the orthographic code. However, recent empirical research has found that students with dyslexia, who tend to make more errors related to word merging and segmentation than students without writing difficulties, do not seem to have accurate orthographic representations of the words they are trying to spell, particularly of the beginnings and endings of words. Therefore, the general aim of this study is to explain spelling errors occurring at word boundaries in dyslexic children. To our knowledge, no typical trajectory of development has been established for normally-developing readers/writers with regards to knowledge of lexical boundaries. Therefore, using both cross-sectional and longitudinal analyses, this study’s first objective is to describe the performances of normally-developing reader and writers from kindergarten to grade 4 on tasks related to lexical boundary knowledge (Study 1). With this developmental reference having been established, the second study will evaluate lexical boundary knowledge in primary school students with dyslexia (study 2). To evaluate ability in reading and word production, a reading test from the K-ABC battery and a dictation task requiring students to insert words in the context of a sentence were administered. To evaluate knowledge of lexical boundaries, three tasks (a lexical decision task, a lexical identification task, and a lexical permutation task) were completed by all participants in oral and written form, each of which varied according to the level of cognitive constraint involved in completing the task.

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This dissertation investigates how cognates are organized in the bilingual mental lexicon and examines whether orthography in one language, via phonological representations, influences the processing of cognates and false friends in the other language. In light of the framework of two well-known models of bilingual visual word recognition, the Bilingual Interactive Activation (BIA) and the Bilingual Interactive Activation Plus (BIA+), the premise is that there is activation from orthography to phonology across a bilingual’s two languages and that this activation is modulated by the degree of orthographic and phonological code overlap. Two objective metrics were used to assess crosslinguistic similarity of Portuguese-English cognates and false friends that were selected for a cross-language lexical decision task with masked priming. Dynamic time warping (DTW), an algorithm that was originally conceived to compare different speech patterns in automatic speech recognition and to measure acoustic similarity between two time-dependent sequences, was used to compute crosslinguistic phonological similarity. The Normalized Levenshtein Distance (NLD), an algorithm that calculates the minimum number of single-character insertions, deletions or substitutions required to change one word into another and normalizes the result by their lengths, was used to compute crosslinguistic orthographic similarity. Portuguese-English bilinguals who acquired their second language after reaching puberty, and English functional monolinguals who grew up speaking primarily English were recruited to participate in the experimental task. Based on collected reaction time and accuracy data, mixed-effects models analyses are used to estimate the individual effects of crosslinguistic orthographic, phonological and semantic similarity and the role each of them, along with English proficiency, word frequency and length play in the organization of the Portuguese-English bilingual mental lexicon.