The effect of a moving background on aimed hand movements.

The performance of aimed hand movements should be carried out safely and without unexpected disturbances. We investigated to what extent movement trajectories are affected by large moving stimuli in the environment. It could be shown that the start of the movement of a structured background may cause a distinct shift of the hand in the direction of the stimulus. Normally this transient effect is compensated by corresponding counter movements of the hand. A continuous background movement does not lead to a significant shift of the movement trajectories during typical eye-hand co-ordination. However, visual tracking of a stylus held by the hand during the course of the move also results in a clear shift. The presented results demonstrate that in the working environment, close to large moving machinery parts, optical aids should provide sufficient cues to stabilize the exocentric reference system, for the performance of aimed hand movements.