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Abstract:
Abstract: Studies of the activity of single cells in the
parietal lobe of macaques (e.g., Snyder et al., Nature, 1997)
suggest that this part of the brain plays a role both in directing
and optimizing perception (attention) and directing action
(intention). Patients with unilateral damage to the parietal lobe
and parieto-temporal junction may have visual hemineglect. Studies
of these patients have repeatedly shown that they have difficulty
perceiving or acknowledging stimuli contralateral to their lesion.
In contrast to the macaque literature, work on these patients has
often concentrated on the attentional aspects of their deficit.
Here we investigate the ability of patients to respond to stimuli
in their contralesional and ipsilesional field. As predicted, all
patients were slower to make responses to stimuli in their
contralesional field, supporting the notion that lesions to the
parietal lobe lead to a deficit in attention. In addition, we
required one of two different responses according to the nature of
the stimulus presented. Changing the nature of the response led to
an increase in reaction time and error rate, suggesting that a
change of intention had to be encoded. This reaction time cost was
greatest in the contralesional field, supporting the notion of a
deficit in intention. This intentional deficit could be seen in
recovery even in the absence of an attentional deficit.
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