Article

It is widely accepted that the posterior parietal cortex is critical for the
on-line control of action and optic ataxia patients are unable to correct their
movements in-flight to changes in target position. The current study investigated
on-line correction in patients with left visual neglect, right brain damaged
patients without neglect and healthy controls. Participants were asked to reach
towards a central target that could jump unexpectedly, at movement onset, to the
right or left sides of space. In response to the jump, participants were asked
either to follow the target or to stop their movement. Neglect patients were able
to correct their ongoing movements smoothly and accurately towards right and left
target jumps. They did so even when told to stop their movement, indicating that
these corrections occurred automatically (i.e., without instruction). However,
the timing of corrections to the left was delayed in neglect patients and this
produced a drastic increase in movement time. To our surprise, we also found that
neglect patients were impaired at stopping their ongoing reaches, when compared
to the control groups, in response to either left or right jump trials. We
suggest that the 'automatic pilot' system for the hand is spared in neglect, but
its processing speed is unilaterally slowed due to a deficit in orienting of
attention to the contralesional side. We relate these findings to the breakdown
of a system that combines information for attention, perception and action.
Damage to this system may not only slow corrective movements to the
contralesional side, but also produce non-lateralized deficits in interrupting an
ongoing reach.
CI - Copyright (c) 2011 Elsevier Ltd. All rights reserved.

Langue : ANGLAIS