[Errors in pointing under various body orientation relative to the gravity vector]

Errors in pointing to remembered target locations were measured in healthy subjects in upright, supine and prone positions, i.e. in three positions differing in body and arm movement orientation relative to the gravity vector. The X-error was unaffected by the body position, whereas the Y-error was dependent on subject's orientation relative to the gravity vector. In two lying positions, the subjects pointed below and in the vertical posture above the remembered target locations. On the contrary, the variable error was differentially affected by orientation of the movement trajectory relative to the gravity vector. In the supine position, the variable error was larger and in the prone position, smaller than in the upright posture. The gravity bias in pointing errors suggests that the motor program generated in the lying position is not modified to adapt to altered orientation relative to the gravity vector.