Many individuals with moderate and severe TBI may experience lack of coordination, weakness, and a loss of fine motor control. Motor dyscontrol impacts balance, activities of daily living and ambulatory capacity. Therapies to improve functional capacity have met with varying success and the resources required for such interventions have been extensive. While individuals recover elements of extremity function after stroke or TBI, the problem of motor dyscontrol remains. Understanding the gaps between real and perceived performance may help to enhance motor training. A technique that could employ robotic assisted rehabilitation while utilizing perceptual gaps (the difference between perceived and true ability) would have unique advantages. Disturbed perception to the extent of possible movement (false perception of ability) has been implicated as a potential factor inhibiting motor recovery. This concept is vitally important for persons with stroke or TBI, since brain damage tends to produce wide perceptual gaps. Robotic intervention has been shown to provide additional goal-directed sensorimotor feedback among persons with stroke and TBI. Ideally, these robotic techniques should enable the precise recording of movements and variable force applications to an affected limb, making it an effective strategy for motor rehabilitation. Robot-assisted rehabilitation has been shown to enhance arm movement recovery. Studies have shown that primates with upper extremity impairment can regain functional skills utilizing robotic devices. There is no difference in the pain level or range of motion of patients treated by robots. In fact, robots have been found to improve the patients. mobility and strength to the same point or to a greater extent, than that which is often achieved by human-assisted therapy. However, none of the currently available robotic systems utilize perceptual manipulation. In this pilot study, the parameter that wil!l be a major focus is referred to as the .just noticeable difference. (or JND). The value of this parameter is defined as the amount of change in a stimulus that is required for an individual to reliably distinguish between two separate and different stimulus intensities. If we can stay within the .just noticeable difference,. we can create an intervention where functional and mobility parameters can be improved without conscious effort of the person with the impairment. The objective of this pilot study is to utilize a novel virtual reality and robotic environment to 1) understand the gaps between real and perceived performance among persons who have suffered a stroke and also have upper extremity motor impairment and 2) to establish and evaluate a .rehabilitation by distortion technique..