Feedback distortion for rehabilitation: gauging perceived physical effort

We examined subjects' perceptions of physical effort in the presence of feedback distortion as they were asked to resist forces produced by a haptic device. Subjects pressed against a simulated spring with the index finger until they reached a target force, which they held for a designated time duration. Visual feedback of the target force level and the designated time duration was provided. On some trials, the visual feedback of force was distorted by 7% to 22% so that subjects produced that much more force to get to the same visual target force. Subjects rated their perceived physical effort for each trial. Our regression analyses showed that rated effort was strongly predicted by the visual feedback of force regardless of the actual force produced. The length of time the force was produced only weakly predicted the rated effort. These results will be used to construct virtual rehabilitation environments.