Our previous work has shown that visual distortion of subject-controlled goals can be used to manipulate force production and movement distance. Thus, visual distortion may be a helpful addition to robotic rehabilitation for brain-injured and stroke patients. In this work, we investigated the effects of distortion on unimpaired subjects learning a two-finger coordinated pinch task. Rather than distorting the subject's goal, we enhanced the apparent error attributable to one or both fingers. Distortion affected the distribution of attention between the two fingers; when the error enhancement was given to one finger, the performance of that finger improved relative to the other. This result indicates that enhanced visual error could be used to manipulate the performance and the coordination pattern between fingers to achieve desired movements during rehabilitation

We create a robotic rehabilitation environment that distorts the visual feedback of a movement representation to restore lost movements. The use of visual-feedback distortion produces a perceptual gap between the perceived (visual) and actual somatosensory experiences, in which movements can be manipulated without patients' knowledge. Previously, we reported the smallest amount of distortion that is imperceptible by measuring just noticeable difference (JND), the distortion size that is tolerable without detection, and the invariance of perceived physical effort under visual-feedback distortion. In this paper, we report the performance changes under visual-feedback distortion in a robotic rehabilitation environment. By interleaving trials with no visual feedback, we showed that the internal somatosensory representation of the movement goal changed along with visual distortion for unimpaired and motor-impaired subjects. In addition, a gradual change of visual-feedback distortion within one experiment allowed movement changes significantly larger than the JND. These changes were robust under sudden lack of visual feedback and even when subjects were informed of possible distortion ahead of time. Finally, preliminary results of a six-week rehabilitation paradigm are reported. Improvements in the patient's hand condition were found, particularly in the range of motion of the index and middle fingers

In order to design a robotic rehabilitation environment using visual feedback distortion, we investigated in this study the limits and effects of visual feedback distortion for the elderly and the motor-impaired. To determine the minimum imperceptible amount of visual distortion, we measured the Just Noticeable Differences (JNDs) for force and position for elderly, unimpaired subjects; values of 31.0% (0.619 N) and 16.1% (5.01 mm), respectively, were obtained. JNDs of 46.0% (0.920 N) and 45.0% (14.8 mm) were measured for a motor-impaired individual. These JNDs were larger than corresponding measurements previously taken with young subjects, showing a decrease in discrimination ability with age and impairment. Visual distortion based on these values caused elderly subjects and the motor-impaired individual to increase their force production levels by 72.5% and 97.7%, respectively. These results were similar to those obtained with young subjects, but differences were observed on interspersed trials with no visual feedback. Poor discrimination abilities in elderly and impaired subjects and visual dominance in our environment for this subject group support our hypothesis that visual distortion can be an effective tool for rehabilitation in a robotic environment.