The egocentric reference deviation of neglect patients is influenced by visuospatial attention.
Résumé
The right deviation of the subjective straight-ahead (SSA), representing a deviation of the body centered spatial reference frame (egocentric reference), is a frequent phenomenon in spatial neglect. Little is known about the influence of visuo-spatial attention on this SSA shift. The aim of this study was to investigate the influence of eye direction (overt attention) and perception of the visual background (covert attention) on the SSA pointing. We included 12 patients with right hemisphere stroke. Six were classified as neglect (N+) and compared to the six non neglect (N-) patients and 19 normal control subjects (C). They had to point straight-ahead (right hand) on an horizontal board. Pointing was performed in the light or in darkness, first with spontaneous eye direction, then while fixating a visual target (-15 degrees , 0 degrees , +15 degrees ). A first ANOVA of factors group, eye direction (left, center, right fixation) and visual context (light, darkness) showed a right SSA deviation in N+ patients only, which was more severe in the light than in darkness. In this group, the SSA was shifted in the same direction as the target, while that of N- and C groups was mildly shifted in the opposite direction. The comparison of spontaneous and central fixation conditions also showed an eye direction by group interaction, as the spontaneous right SSA deviation was reduced by central fixation in N+ patients only. These results suggest that, in neglect patients, the egocentric reference deviation is not a fixed phenomenon, and that it can be influenced by manipulation of both overt and covert spatial attention.