How do handwriting and spelling influence each other ? Investigation of writing development in children with and without dyslexia

Writing constitutes a crucial communication tool in everyday activities, whether in education, social, or professional life. The cognitive and motor processes involved in writing are numerous and complex, and learning to spell and to handwrite is a long-lasting challenge during childhood. While most children achieve mastery of writing abilities without too much trouble, children with dyslexia have a persistent spelling impairment, making writing acquisition even more challenging. Moreover, past research has highlighted that such children also have slower or poorer handwriting than their peers. However, while spelling and handwriting are inevitably related, these skills have been traditionally studied separately. Consequently, the current literature does not hold a clear picture of the concurrent development of spelling and handwriting. Furthermore, the nature and the origin of children with dyslexia’s handwriting difficulties are not established, and the presence of a graphomotor deficit in dyslexia is debated. This doctoral dissertation seeks to contribute to the understanding of the development of spelling and handwriting in children with and without dyslexia. More specifically, we wanted to address two research questions: how do spelling and handwriting develop and influence each other during writing development? (Objective 1), and do children with dyslexia present a graphomotor deficit? (Objective 2). These objectives were addressed through five empirical studies conducted in samples of French-speaking children. In each study, measures of spelling accuracy, handwriting speed and legibility were collected during writing tasks. The use of robust experimental designs, i.e. longitudinal, interventional and neuroimaging, led to valuable contributions to the field of writing research and dyslexia. Our longitudinal findings highlighted significant associations between spelling and handwriting in typical development. Spelling and handwriting speed were found to be positively related throughout development. In contrast, handwriting legibility seems to develop rather independently from spelling. Importantly, the causal impact of improvements in graphomotor abilities on spelling was demonstrated using an intervention design. We also revealed that the graphomotor demand of words significantly influences the spelling accuracy of beginning writers. This effect fades after Grade 2 in typical development but remains significant in older children with dyslexia. Concerning children with dyslexia, we showed that they have less legible handwriting than their peers. Moreover, neuroimaging evidence highlighted dysfunction in brain regions crucially involved in graphomotor processes. Overall, this dissertation demonstrated that children with dyslexia’s writing difficulties are not limited to spelling and brings evidence in favour of a graphomotor impairment in dyslexia. By allowing a better understanding of the relationships between spelling and handwriting during writing development, these findings convey substantial educational and clinical implications for writing instruction and therapies.(PSYE - Sciences psychologiques et de l'éducation) -- UCL, 202