The disengage deficit in hemispatial neglect is restricted to between-object shifts and is abolished by prism adaptation.

We sought to determine the effects of prism adaptation on peripherally cued visual attention shifting in patients with spatial neglect, using a task devised by Egly et al. (J Exp Psychol Gen 123:161-177, 1994) based on the classic Posner paradigm. This task allowed a comparison of "within-object" versus "between-object" attention shifts. A display was presented containing two parallel outline rectangles, and subjects were asked to make rapid responses to a target, which would appear at one end of one of the rectangles. The target location was pre-cued with 75% validity: on invalid trials attention was directed either to the other end of the same rectangle, or to the other rectangle. Healthy subjects and right-hemisphere patients without neglect showed a left-right symmetrical pattern, with a larger validity effect when required to shift attention between rectangles, thus indicating a greater difficulty of attention-shifting between than within the respective shapes. The neglect patients showed the typical leftward "disengage deficit" previously observed in neglect, but only for attention shifts between objects, indicating that the effect is object-based rather than purely spatial. A comparison of vertical and horizontal shift costs showed that this attention-shifting deficit for left-hemifield target stimuli was directional rather than hemifield-based: it was absent for vertical shifts of attention within the left hemifield. Finally, we found that prism adaptation abolished the disengage deficit. We found no effects of prism adaptation in the control subjects. We argue that prism adaptation has a powerful effect on one of the fundamental manifestations of the neglect syndrome.

Does motor imagery training improve hand function in chronic stroke patients? A pilot study.

OBJECTIVE: To assess the efficacy of motor imagery training for arm function in chronic stroke patients. The relation between mental processes such as attentional and perceived personal control over recovery, and motor imagery was additionally investigated. DESIGN AND SUBJECTS: Twenty patients with long-term motor impairments (mean two years post stroke), were assessed before and after four weeks of training. Ten patients mentally rehearsed movements with their affected arm. Their recovery was compared with patients who performed nonmotor imagery (n =5), or who were not engaged in mental rehearsal (n=5). SETTING: Patients were recruited from the stroke database of Ninewells Hospital, Dundee. Assessment and training were performed at the patients' home. INTERVENTIONS: The motor imagery group was asked to practise daily imagining moving tokens with their affected arm. The nonmotor imagery group rehearsed visual imagery of previously seen pictures. All patients practised physically moving the tokens. MAIN MEASURES: The following variables were assessed before and after training: motor function (training task, pegboard and dynamometer), perceived locus of control, attention control and ADL independence. RESULTS: All patient groups improved on all motor tasks except the dynamometer. Improvement was greater for the motor imagery group on the training task only (average of 14% versus 6%). No effect of motor imagery training was found on perceived or attentional control. CONCLUSIONS: Motor imagery training without supervision at home may improve performance on the trained task only. The relation between movement imagery, attention and perceived personal control over recovery remained unclear.

Memory-driven movements in limb apraxia: is there evidence for impaired communication between the dorsal and the ventral streams?

Memory-driven reaching and grasping movements were analysed in patients with left cerebral hemispheric damage and impaired gesture imitation. The dorsal and ventral streams of the visual pathway model of Milner and Goodale (Milner and Goodale, The Visual Brain in Action, 1995) are thought to operate relatively independently. However, cross-connections between the areas of each pathway are likely to enable interactions essential for higher-level praxis. Apraxic errors such as seen in gesture imitation can possibly be understood as arising from a disconnection of the two visual pathways. If the integrated action of the perceptual and visuomotor systems in patients with apraxia is compromised, then we would expect to find indications of impaired motor programming and misreaching in these patients when making movements driven by stored representations. Such a pattern, however, was not found in our sample of apraxic patients. Patients with limb apraxia produced normal movement kinematics and normal end-point accuracy when making memory-driven reaching movements with or without visual guidance of movement. Furthermore, perceptual information about object size and object distance were incorporated as normal in memory-driven grasping movements of these patients.