Drift in blind reciprocal aiming movements.

There is anecdotal evidence of drift in various reciprocal motor tasks, but as far as is known, no investigations into this phenomenon have been reported. Yet, systematic drift can potentially explain a significant proportion of the total variability in motor output. Three experiments were conducted to ascertain the nature of drift in reciprocal aiming tasks and to develop methods and measures to isolate and quantify drift for analyses. We also evaluated a computational posture-based model of reaching movements with respect to the findings of the experiments. Drift was observed in all three experiments, generally toward the middle of the joint motility range. Simulations based on the model produced drift to the middle of the task movement range rather than middle of the joint movement range. Adding noise to the model could increase its power for simulating the underlying principles of movement control as reflected in performance features such as drift.