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Prism adaptation reduces some symptoms of neglect; however the mechanisms underlying such changes are poorly understood. We suggest that prisms influence neglect by acting on dorsal stream circuits subserving visuomotor control, with little influence on perceptual aspects of neglect. We examined prism adaptation in three neglect patients and a group of healthy controls on line bisection and landmark tasks. Neglect patients showed a dramatic reduction in the rightward bias for line bisection, but absolutely no change in their leftward bias on the landmark task, which is a perceptual equivalent to bisection. However, in controls, prisms produced 'neglect-like' deficits on both the line bisection and landmark tasks. These data suggest that prisms influence visually guided actions more so than perception in neglect.

International audience; Earlier research has suggested that optic ataxia, a deficit in reaching in peripheral vision, can be isolated from Balint's syndrome as it is primarily a visuomotor disorder, independent of perceptual or attentional deficits. Yet almost no research has examined the attentional abilities of these patients. We examined peripheral visual attention in two patients with unilateral optic ataxia. Results indicated that both patients were slower to respond to targets in their ataxic visual field, irrespective of cuing condition (i.e. validly, invalidly, and no cue conditions), consistent with an overall decrease in the salience of stimuli in the ataxic field. Attentional deficits in peripheral vision are therefore an important factor to consider when examining visuomotor control deficits in optic ataxia.

Recent research has shown that prism adaptation alleviates some of the symptoms of neglect. Although prism adaptation can aid patients with neglect, the mechanisms underlying these benefits remain largely unknown. One way in which prisms may work is by altering attentional orienting mechanisms known to be impaired in neglect. To investigate this hypothesis, we tested four right brain damaged patients (two with neglect) on a reflexive covert attention task before and after rightward prism adaptation and compared them with a group of healthy controls who underwent sham prism adaptation. Results demonstrated that rightward prism adaptation reduced both the rightward attentional bias, and the disengage deficit in patients with right brain damage irrespective of the presence of neglect.

Patients with schizophrenia demonstrate impairments indicative of an inability to accurately monitor internally generated images. Motor imagery measures the ability to generate internal images of intended but not executed motor movements. Ten patients with schizophrenia completed actual and imagined versions of a pointing task with a well defined speed-accuracy trade-off function. For controls, movement time increases as target size decreases for both actual and imagined movements. Despite showing the expected speed-accuracy trade-off for actual movements, the imagined movements of schizophrenics showed no reliable relationship to target size. This was true for each patient and appeared to be independent of symptom profile. These results suggest that patients with schizophrenia are unable to generate accurate internal images of their own motor movements.

Patients with parietal lesions often fail to identify stimuli in the contralesional field (i.e. neglect) but may nevertheless demonstrate implicit processing of neglected stimuli. Explanations of implicit processing in neglect range from intact preattentive mechanisms, to intact higher level categorical processing. Such theories assume implicit processing in neglect is passive and not subject to attentional modulation. We investigated implicit processing in a neglect patient US) using a flanker task in which targets differed on two dimensions simultaneously (i.e. coloured letters). Controls demonstrated interference effects only from goal-relevant dimensions of flankers. JS showed a similar pattern of results even when flankers appeared in his neglected field, suggesting that implicit processing of neglected stimuli can be modulated by behavioural goals.