The nature of acquired dysgraphia: patterns of impairment and rehabilitation

This thesis focuses on the processes involved in spelling, and in particular explores the nature of impairment and rehabilitation of acquired dysgraphia, using a cognitive neuropsychological approach. The first study investigates the spelling impairment of GEC, a man with acquired dysgraphia. GEC showed characteristics of graphemic output buffer impairment, together with lexical influences (e.g., frequency) on performance and a large number of deletion errors of multiple letters (fragment errors). A detailed error analysis provided evidence to support the hypothesis that fragment errors can be the result of rapid decay of activation from the graphemic output buffer. The study also concludes that lexical influences could be observed in graphemic output buffer impairment due to cascading of activation. The second study investigates the nature of acquired sub-lexical spelling impairments. Data from spelling sounds in isolation and spelling non-words are analysed to inform three issues: the relationship between performance on the two spelling tasks, the effects of phoneme-grapheme consistency and frequency on spelling, and the use of context when spelling a vowel in a non-word. Results indicated that people with aphasia show comparable difficulty spelling single sounds and sounds in initial position of the non-word. Furthermore, accuracy of individual PGCs was influenced by frequency and consistency of the non-word. Finally, no evidence was found for a loss of context sensitive rules when spelling vowels. The final two studies focus on rehabilitation of acquired dysgraphia. Study three comprises a literature review on generalisation effects after treatment of acquired dysgraphia. This study summarises forty treatment studies, investigating the link between type of impairment, method of treatment, and generalisation. Some treatment studies in the literature have found an improvement in untreated items, however it is unclear what predicts such generalisation of treatment effects. Study three highlights that a mechanism of interactive processing may play a role in treatment and generalisation. The final study therefore investigates this mechanism of interactivity within the spelling process in two treatment studies examining the role of orthographic neighbourhood size on the effects of treatment and generalisation in two individuals with acquired dysgraphia. Feedback between the orthographic lexicon and the graphemic output buffer predicts a target word will activate orthographically related words. However, while treatment improved spelling for treated items, there was no generalisation and no evidence for effects of orthographic neighbourhood size on treatment. It was hypothesised that severe impairment to the graphemic output buffer reduced the feedback within the spelling system. This thesis contributes to our understanding of the nature of spelling impairment and rehabilitation. Furthermore, the thesis highlights the value of cognitive neuropsychological methods in research of acquired dysgraphia.