Dyslexia is defined as the difficulty learning to read despite adequate intelligence, instruction and socioeconomic opportunity. The range of figures given for the prevalence of the disorder is from 3-15%. Many of these children appear to have phonological and/or visual processing deficits that persist well into adulthood. It is important that we more fully understand these deficits and how they affect reading in order to advance remediation and intervention strategies. This study will compare the performance of adult readers with dyslexia, selected on the basis of a childhood history of dyslexia, discrepant performance on standardized reading tests and a specific visual processing deficit, to the performance of normal controls (matched on PIQ) on tasks of attentional and orthographic processing. The first phase of the project will be to obtain normative data from a coherent motion detection task, and to select dyslexic readers who demonstrate a deficit compared to the normal distribution. Following the recruitment of matched normal control subjects, the next step will be to assess both groups of subjects' attentive and pre-attentive processing in the visual modality using various types of visual search tasks. Lexical decision tasks will then be administered to both groups of subjects in order to determine the independent contribution of any sensory or attentional deficit to orthographic processing. The final set of experiments will look for differences in patterns of brain activity between the individuals with dyslexia and the normal controls using functional Magnetic Resonance Imaging (fMRI) methods.
