Is dyslexia more than a reading and spelling problem? An evaluation of the 'cerebellar deficit hypothesis'

Objectives: The ‘Cerebellar Deficit’ hypothesis of developmental dyslexia proposes that, due to mild cerebellar dysfunction, dyslexic individuals demonstrate a general automatisation deficit on both motor and cognitive tasks. This study aims to evaluate the hypothesis and seeks to determine whether the severity of dyslexia and/or the presence of comorbid learning difficulties such as ADD/ADHD, may be factors associated with the presence/absence of automatisation. The British Psychological Society 282 2003 Proceedings deficits. Design: A dyslexic case group is matched with chronological-age and reading-age control groups. Methods: 50 case boys, age seven to 12, with an independent psychological assessment that confirms a diagnosis of dyslexia, have been contacted via the Dyslexia Institute or local British Dyslexia Association support groups. Each case boy is matched with two control children, resulting in 50 controls matched on chronological age and 50 controls matched on reading age. In the first phase of this study, each boy is assessed on measures of attention, temporal judgement, balance and co-ordination, phonological awareness and rapid naming. Results & Conclusions: Collection of case data is complete and control data is in the process of collection. Results from the dyslexic group are considered in terms of severity of dyslexia and the presence or absence of additional learning difficulties. Results are also discussed in terms of their implications for the ‘cerebellar deficit’ hypothesis and for causal theories of dyslexia in general, where a lack of consideration of possible interactions with other learning disorders may have been misleading.