Motor performance and motor learning in adults with dyslexia
Assessment of motor performance and motor learning in dyslexia is crucial because of its ability to shed light on the underlying biology of the disorder and to discriminate between theoretical approaches. It remains a controversial area due to existing discrepant research findings and interpretations. Three studies are described in this thesis. The first used three sets of experiments to test balance and postural control in single and dual-task conditions. The second study examined the production and timing of responses in a classical eyeblink conditioning paradigm. The final study investigated motor skill acquisition. The results of the three studies were similar in that in dual-task balance, conditioned response timing and motor skill consolidation around half of the dyslexic adults showed substantial deficits compared with a control group. The samples of participants in the three studies overlapped sufficiently for some cross-study comparisons of strengths and weaknesses to be conducted. These showed that it was rare for a participant with dyslexia to show motor impairment in just one of the three domains, with dual task balance and conditioned response timing seeming to be most closely associated. Overall the results provide strong evidence of enduring deficits outside the literacy domain in dyslexia and also highlight the considerable heterogeneity of the disorder. Consequently they lend particular weight to the notion of cerebellar causation. Further studies should be undertaken on a larger scale to scrutinize the consistency of motor impairments in dyslexia and the possibility that those showing motor problems might form a definite subgroup within dyslexia. In the longer term, this work points to a possibility of multiple, independently diagnosable sub-classes of dyslexia, based on specific neurological abnormalities, with their own specific remediation and objective early detection schemes.