Gravitational inputs modulate visuospatial neglect

Right brain-damaged patients with left visuospatial neglect were required to bisect a line placed in front of them in two different body positions (upright and supine) and two different light conditions (light and dark). The neglect patients, unlike right brain-damaged patients without neglect, strongly reduced their rightward directional error in the supine compared with the upright position. No systematic changes were produced by the light-dark manipulation. The present result cannot be explained with an attentional interpretation of hemispatial neglect. We suggest that the present data provide further evidence that hemineglect is the consequence of a mismatch between different afferent information integrated into an egocentric space representation. According to this model, the presence of a lateralized brain lesion produces asymmetries in some intermediate spatial representations (eye-head, head-trunk, body-environment) but not in the retinotopic one. Any experimental manipulation that reduces the asymmetry of the intermediate representation such as the reduction of gravitational inputs may improve the dynamic integration of the egocentric coordinates.