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Abstract:
The close relationship between the control of real and
imagined movements has been well-demonstrated behaviourally and
through functional neuroimaging. In general, imagined performances
closely resemble actual performances and make use of overlapping
neural circuitry. Some patients with parietal lobe injuries
demonstrate contralesional impairments in imagined movements such
that imagined movements do not conform to expected speed-accuracy
trade-off functions. We tested one patient with spatial neglect
following a right parietal injury using a visually guided pointing
task in which both real and imagined movement duration (MD) is
expected to increase as target size decreases. Despite
demonstrating a normal speed-accuracy trade-off for actual
movements, the patient showed no significant relationship between
MD and target size when asked to imagine making movements,
irrespective of the hand used or the initial direction of movement.
This poor motor imagery performance was in the context of normal
visual imagery as tested on a range of standard clinical tasks. The
patient was also asked to make actual movements while imagining a
previously presented target. In this condition the relationship
between target size and MD was stronger than when the entire
movement had to be imagined. This suggests that this patient
requires visual and kinesthetic feedback of the moving hand in
order to demonstrate a reliable speed-accuracy trade-off for
visually guided movements.
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