Bambi R. Brewer

Perceptual limits for a robotic rehabilitation environment using visual feedback distortion

Imperceptible visual distortion, in the form of a disguised progression of performance goals, may be a helpful addition to rehabilitation after stroke and other brain injuries. This paper describes work that has been done to lay the groundwork for testing this hypothesis. We have constructed and validated an experimental environment that provides controllable visual distortion and allows precise force and position measurements. To estimate the amount of visual distortion that should be imperceptible, we measured the limits for force and distance/position perception in our rehabilitation environment for young and elderly unimpaired subjects and for a single traumatic brain injury (TBI) patient. We found the Just Noticeable Difference (JND) for produced force to be 19.7% (0.296 N) and the JND for movement distance/finger position to be 13.0% (3.99 mm) for young subjects (ages 18-35). For elderly subjects (ages 61-80), the JND for force was measured to be 31.0% (0.619 N) and the JND for distance/position was 16.1% (5.01 mm). JNDs of 46.0% (0.920 N) and 45.0% (14.8 mm) were found for the motor-impaired individual. In addition, a subjects rating of effort was found to be profoundly influenced by visual feedback concerning the force magnitude. Even when this feedback was distorted, it accounted for 99% of the variance of the effort rating. These results indicate that substantial visual distortions should be imperceptible to the subject, and that visual feedback can be used to influence the subjects perceived experience in our robotic environment. This means that we should be able to use imperceptible visual distortion to alter a patients perception of therapeutic exercise in a robotic environment.

Visual feedback distortion in a robotic environment for hand rehabilitation

Robotic therapy offers a means of enhancing rehabilitation for individuals with chronic stroke or traumatic brain injury. The present research targets members of this population who demonstrate learned nonuse, a tendency to use affected limbs below the level of the individuals true capability. These individuals may not strive for difficult goals in therapy, which ultimately hampers their progress and the outcome of rehabilitation. Our research uses a paradigm called visual feedback distortion in which the visual feedback corresponding to force or distance is gradually changed by an imperceptible amount to encourage improved performance. Our first set of experiments was designed to assess the limits of imperceptible distortion for visual feedback concerning the force exerted or the distance moved by the index finger. A second set of experiments used these limits to gradually distort visual feedback in order to manipulate a subjects force or distance response. Based on this work, we designed a paradigm applying visual feedback distortion to the rehabilitation of individuals with chronic stroke and traumatic brain injury. Initial tests are reported for two subjects who participated in a six-week rehabilitation protocol. Each patient followed visual feedback distortion to levels of performance above that predicted by her performance during an initial assessment. Both patients showed functional improvements after participating in the study. Visual feedback distortion may provide a way to help a patient move beyond his or her self-assessed best performance, improving the outcome of robotic rehabilitation.

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.

Using visual feedback distortion to alter coordinated pinching patterns for robotic rehabilitation

BackgroundIt is common for individuals with chronic disabilities to continue using the compensatory movement coordination due to entrenched habits, increased perception of task difficulty, or personality variables such as low self-efficacy or a fear of failure. Following our previous work using feedback distortion in a virtual rehabilitation environment to increase strength and range of motion, we address the use of visual feedback distortion environment to alter movement coordination patterns.MethodsFifty-one able-bodied subjects participated in the study. During the experiment, each subject learned to move their index finger and thumb in a particular target pattern while receiving visual feedback. Visual distortion was implemented as a magnification of the error between the thumb and/or index finger position and the desired position. The error reduction profile and the effect of distortion were analyzed by comparing the mean total absolute error and a normalized error that measured performance improvement for each subject as a proportion of the baseline error.ResultsThe results of the study showed that (1) different coordination pattern could be trained with visual feedback and have the new pattern transferred to trials without visual feedback, (2) distorting individual finger at a time allowed different error reduction profile from the controls, and (3) overall learning was not sped up by distorting individual fingers.ConclusionIt is important that robotic rehabilitation incorporates multi-limb or finger coordination tasks that are important for activities of daily life in the near future. This study marks the first investigation on multi-finger coordination tasks under visual feedback manipulation.

Feedback distortion to overcome learned nonuse: a system overview

We constructed a virtual environment that is designed to use visual feedback distortion to address Learned Nonuse in stroke patients. The system is intended to rehabilitate finger movements, and it includes haptic and visual displays. The virtual environment includes custom-made hardware and software that allow the force feedback to adapt to different individuals and to movement changes over time for a single individual. Using this environment, we conducted a preliminary experiment with unimpaired subjects to show that it is possible to extend the range and strength of movements without subjects recognizing the visual feedback distortion.

Initial Therapeutic Results of Visual Feedback Manipulation in Robotic Rehabilitation

Visual feedback is provided to patients in most robotic rehabilitation applications, and this feedback has the potential to influence patient performance in therapy. We have explored the use of visual feedback manipulation (by distortion or progression) in rehabilitation with 3 subjects, each of whom participated in a 6-week rehabilitation protocol. Patients performances during the initial assessment at each therapeutic session were found to be an underestimate of their actual abilities and were a poor metric for setting the difficulty level of therapeutic exercise. All three patients were willing and able to improve their performance by following distortion or progression, and all patients showed functional improvements after participation in the study. Visual feedback manipulation could provide a way to go beyond patients self-assessment performances, improving the outcome of robotic rehabilitation

Enhanced visual error in a coordinated pinch task

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 subjects 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

Shaping synergistic pinching patterns with feedback distortion in a virtual rehabilitation environment

Individuals with chronic disabilities often use compensatory coordination patterns learned during the recovery phase, even after their individual muscular control returns. Although these compensatory movements limit their ability to complete tasks, these individuals are not able to relearn the correct synergistic coordination patterns because doing so would temporarily compromise task performance. Following our previous work using feedback distortion in a virtual rehabilitation environment to increase the strength and range of motion of disabled individuals, we address the use of this same feedback distortion environment to alter movement coordination patterns. In this paper, we present the methodology and preliminary results showing that (1) able-bodied individuals could be trained to use a different coordination pattern to produce pinching movements, and (2) feedback distortion can alter movements for individual fingers separately during a coordinated movement. These results indicate that our distorted virtual environment may be a powerful rehabilitation tool to convert compensatory movements into movements that utilize all muscles in the normal synergistic patterns.