Pointing and bisection in open and closed loop reaching in patients with hemispatial neglect
It is well established that patients with hemispatial neglect present severe visuospatial impairments, but studies that have directly investigated the visuomotor control in these patients have revealed diverging results, some pointing to relatively spared visuomotor function. The present study compared the performance of 8 patients with hemispatial neglect and 10 without the disorder after right hemisphere stroke and 10 age-matched controls. Subjects were asked to point either directly towards targets or in the middle of two targets, both with and without visual feedback of the hand and target during movement. No specific impairments were observed for the neglect patients on either timing, speed and end-point accuracy measures for any of the conditions. Despite the failure of our neglect patients to react to stimuli on the contralesional side of space when assessed with paper and pencil tests, we did not find any specific deviations in their movements. Our results suggest that the perceptual distortions present in patients with neglect do not influence their performance on pointing tasks with or without visual feedback of their hand, supporting the view that such patients code spatial parameters for action veridically.
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ABSTRACT: Milner and Goodale (The visual brain in action, Oxford: Oxford University Press, 1995; The visual brain in action, 2nd ed., Oxford: Oxford University Press, 2006) propose a model of vision that makes a distinction between vision for perception and vision for action. One strong claim of the model is that the dorsal stream's control of action is designed for dealing with target stimuli in the ‘here and now’, yet when time is allowed to pass and a reaction has to be made on the basis of a visual memory, the ventral stream is required for successful performance.Regarding the syndrome of hemispatial neglect, Milner and Goodale further claim that the visual dorsal stream is relatively spared in these patients. In the current study we tested whether neglect patients would indeed be unimpaired in immediate pointing, yet show inaccurate pointing in a condition where a delay is interposed between the presentation of the stimulus and the response signal (in particular in left space). We tested the ability of nine neglect patients (and healthy and right hemisphere no neglect control groups) to perform reaches towards immediate and delayed targets, placed in left, central and right locations. Neglect patients showed no accuracy impairments when asked to perform an immediate action. Conversely, when pointing towards remembered leftward locations, they markedly overshoot the target or failed to initiate a reach altogether. These results confirm that patients with neglect are not specifically impaired when performing ‘here and now’ actions, but rather present deficits when the visuomotor task taps into more perceptual ‘off-line’ representations thought to depend on ventral visual stream activation.Neuropsychologia 05/2009; 47(6-47):1563-1572. DOI:10.1016/j.neuropsychologia.2008.08.008 · 3.30 Impact Factor
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