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Abstract:
Abstract: In the double-step saccade task (DSST) the accuracy
of the second saccade depends upon the predicted outcome of the
first. Single unit studies show this operation is achieved through
the dynamic re-organisation of visual and motor neurons so that
their receptive fields predict the sensory consequences of the
first saccade before it is executed. In humans, the accuracy of
second saccades is reduced only with focal parietal cortex lesions.
The DSST was used to test the hypothesis that children with
Developmental Co-ordination Disorder (DCD) have difficulty
processing the visual spatial properties of intended movements
using efference copy signals. DSST performance was compared between
healthy adults, healthy children and children with DCD. The
distribution of latencies of first saccades in double step saccade
ensembles was bimodal. Analysis of saccade accuracy, intersaccadic
interval suggested that double-step saccade ensembles from the
second slower mode were programmed using forward models of
efference copy. Children with DCD displayed specific deficits on
the DSST where efference copy had been used to program the saccade
sequence. The DCD group were less accurate in terms of endpoint on
second saccades of the slow mode ensembles. This suggests that
impaired processing of efference copy signals could underlie motor
clumsiness in DCD.
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