User comprehension of task performance with varying impedance in a virtual prosthetic arm: A pilot study

Humans' ability to modulate the mechanical impedance of their arms is crucial for adapting the behavior of their arms for use in different tasks. Previous research has shown that user-selectable impedance in prosthetic arms can enable better performance in disparate tasks and changing environments. However, user-selectable impedance is only useful to a prosthesis user if he or she can learn to modulate the impedance effectively. In this paper, we report the results of a pilot study investigating subjects' ability to evaluate their own performance in an interaction task under different impedance levels, with the goal of identifying factors that may affect users' ability to choose effective impedance levels. Subjects controlled a one-degree-of-freedom virtual prosthesis under different stiffness and damping levels to perform an interaction task in which they attempted to minimize contact forces from a virtual environment. We compared subjects' task performance to their perceived difficulty of the task under different impedance conditions. We show that with appropriate training and feedback scaling, subjects are able to evaluate their task performance with both visual and vibrotactile feedback of force information. The results of this study suggest approaches to enabling subjects to choose effective impedance levels for different tasks, and may aid in the development of prostheses and telerobotic systems with user-selectable impedance for more natural and efficient interactions with the environment.