Fig. 6.

Tilt during lift. A: mean and SE of the tilt with respect to the instructed tilt vs. the height of the object. In all cases a tilt of 0 indicates perfect performance, negative tilt indicates a rightward error with respect to the subject, and positive tilt indicates a leftward error. Control subjects were successfully able to lift the object in the instructed direction in all cases. PD subjects could only maintain the instructed tilt when the object was lifted vertically. For the tilted objects, PD subjects allowed the objects to tilt toward vertical, as they would by the gravitational force. To capture the tilt, B shows the tilt averaged over 4–6 cm in height (indicated by gray shading in A, top left) with SE. In all cases, control subjects were within error bars of 0, although they had a consistent tendency to allow the asymmetric object to tilt rightward and overcompensated on the symmetric object, tilting it leftward. Off medication, PD subjects show significant tilts for the left and right objects and do not correctly compensate for the weight distribution of the asymmetric object, allowing it to tilt farther rightward (down on the plot) in all cases. This effect was not alleviated by medication.