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Abstract:
Abstract: The use of spatial information for action was
studied by analyzing pointing performances in a specially
elaborated motor task requiring memorization of proprioceptive
targets. Without visual control, the targets locations were encoded
during a brief passive positioning of the left index finger on the
target. A go-signal for matching target location with the right
index finger was provided either 0 or 8 seconds later. The six
targets were located on a sagittal plane, on an arc centered on the
starting point. Errors made during hand-pointing were measured. In
controls, the main axis of the endpoints distribution tended to be
aligned with the target array in the 8-s-delay condition, but not
in the 0-s-delay condition, demonstrating the capability of using a
contextualized mental representation in delayed pointings. Neither
Schizophrenics nor HD patients followed this tendency,
demonstrating that patients from both groups were not able to use
the contextual information provided by the target array. In the 3
groups, precision, as measured by the surface of the clouds of
endpoints, was higher in the 0-s-delay condition than in the
8-s-delay condition. HD patients, but not Schizophrenics,
demonstrated a significantly decreased precision in both
conditions. Interestingly, precision is thus normal in
Schizophrenics in the delayed condition. Results from
Schizophrenics and HD patients are compared and discussed.
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