Human Adaptation to Dynamic Interaction Forces During
Learning of a Visuo-motor Task
Felix C. Huang, R. Brent Gillespie, and Arthur D. Kuo
to appear: IEEE Transactions on Neural Systems and Rehabilitation Engineering
We tested whether humans can learn to sense and compensate for interaction
forces in contact tasks. Many tasks, such as use of hand tools, involve
significant interaction forces between hand and environment. One control
strategy would be to use high hand impedance to reduce sensitivity to these
forces. But an alternative would be to learn feedback compensation for the
extrinsic dynamics and associated interaction forces, with the potential for
lower control effort. We observed subjects as they learned control of a
ball-and-beam system, a visuo-motor task where the goal was to quickly position
a ball rolling atop a rotating beam, through manual rotation of the beam alone.
We devised a ball-and-beam apparatus that could be operated in a real mode,
where a physical ball was present; or in a virtual training mode, where the
ball’s dynamics were simulated in real time. The apparatus presented the same
visual feedback in all cases, and optionally produced haptic feedback of the
interaction forces associated with the ball’s motion. Two healthy adult subject
groups, Vision-Only and Vision-Haptics (each N=10), both trained for 80 trials
on the simulated system, and then were evaluated on the real system to test for
skill transfer effects. If humans incorporate interaction forces in their
learning, the Vision-Haptics group would be expected to exhibit a smoother
transfer, quantified by changes in completion time of a ball-positioning task.
During training, both groups adapted well to the task, with reductions of 64-70%
in completion time. At skill transfer to the real system, the Vision-Only group
had a significant 35% increase in completion time (p < 0.05). There was no
significant change in the Vision-Haptics group, indicating that subjects had
learned to compensate for interaction forces. These forces could potentially be
incorporated in virtual environments to assist with motor training or
rehabilitation.