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.