The visual vertical in the pusher syndrome: influence of hemispace and body position.

The subjective visual vertical (SVV) was investigated in right brain-damaged (RBD) patients with pusher syndrome (PS) which is thought to stem from an erroneous perception of body orientation. The participants, sitting or lying, had to align a luminous rod with gravity. The task was performed in darkness with the rod centred to the body, or placed in the left (neglected) or in the right hemispace. The error, negligible in the control group (+0.3 degrees; n = 6) and mild in the nonneglect non-pusher patients (-1.8 degrees; n = 6), was clearly clockwise in the pusher neglect patients (N+P+; +7.2 degrees; n = 4), but anticlockwise in the non-pusher neglect patients (-6.6 degrees; n = 6). In both neglect groups, error was greater when the rod was in the left space. In N+P+ patients, the performance was strongly affected by posture (lying: +5.2 degrees ; sitting: +9.2 degrees ). Intra-individual variability was also much greater in this group. This study confirms the contralesional deviation of SVV in RBD patients without PS and suggests the presence of an opposite bias in RBD patients affected by PS.