Judgment of the visual vertical and horizontal in patients with Parkinsonism.

Judgment of the visual vertical and horizontal in the upright body position was abnormal in 19 (29 percent) of 66 patients with Parkinson's disease. The magnitude of errors correlated with the degree of rigidity and of tremor in the limbs, but not with bradykinesia or other clinical features. The results suggest that the effect on visual perception of the vertical and horizontal coordinates in patients with parkinsonism is brought about by specific changes in the basal ganglia and is not, as in the case of other visual-motor tasks, determined merely by the overall severity of cerebral pathology.