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Robotic therapy has been shown to increase the range of motion, strength, and velocity of arm movements in chronic stroke patients. Robotic therapy may improve the condition of such patients because it focuses on intensive, repetitive movements, which have been shown to counteract the detrimental effects of a habitual decrease in movement.
We have constructed a robotic environment to combine the repetitive movements of robotic therapy with visual feedback distortion. When an individual performs a task repeatedly, his or her performance on a given attempt is predicted largely by the previous performance. If feedback received by the individual is distorted so that the level of performance appears less than the level previously achieved, the individual will improve performance until the feedback indicates that the previous performance level has been reached. We plan to extend the use of feedback distortion to continuous, progressive distortion during rehabilitation activities with patients with chronic stroke, traumatic brain injury (TBI), and other neurological trauma. Feedback distortion may be particularly useful for these chronic patients because an extended period with little or no improvement may discourage a patient from attempting tasks beyond his or her usual level of function. A robotic environment is appropriate for this research since it allows systematic distortion of the visual feedback relative to the interaction with the robot. We currently focus on small movements of the hand and fingers, but our hypothesis generalizes to other rehabilitation activities. |
| To prevent patients from dismissing the visual feedback as unreliable, we must ensure that the visual distortion in our environment is imperceptible. To that end, we measured the Just Noticeable Difference (JND) for force and position in unimpaired subjects. The JND for a physical dimension is the smallest change in that dimension that can be reliably perceived. Thus, the JNDs for force and position provide a lower bound on the amount of visual distortion that we can expect to be imperceptible. For young subjects (ages 18-35), we found a mean force JND of 19.7% 1.85% (0.296 0.028 N) (mean standard error) and a mean position JND of 13.3% 1.40% (3.99 0.434 mm). For elderly subjects (ages 61-81), we found a mean force JND of 31.0% 3.99% (0.619 0.0797 N) and a mean position JND of 16.1% 1.18% (5.01 0.370 mm).
The force and position JNDs indicate the minimum amount of distortion that should be imperceptible; in fact much larger amounts of distortion may go unnoticed by subjects. In experiments with young and elderly subjects, we have shown that gradual visual distortion leads to increases in force production of 30.0 % (young subjects) and 72.5% (elderly subjects). These increases occurred without detection of the distortion by subjects. The dominance of vision in force production supports our hypothesis that we will be able to use visual distortion to encourage stroke and TBI patients to improve their performance of various physical tasks. Because subjects rely primarily on the visual feedback, a patient may work harder if the feedback is gradually distorted so that better performance is required to achieve the same visual result. This improvement due to distortion should enhance the outcome of the rehabilitation. |
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| Preliminary therapeutic work with a TBI patient used gradual visual distortion of up to 92.0% without the detection of the distortion. This rehabilitation program led to significant increase in the range of motion and maximum force. | |