Effects of visual feedback distortion for the elderly and the motor-impaired in a robotic rehabilitation environment

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.