Virtual reality therapy of multiple sclerosis and spinal cord injury: design consideration for a haptic-visual interface.

Multiple sclerosis and spinal cord injury patients can benefit by interaction with a haptic-visual system to increase the accuracy of movements in cases of spasticity, cerebellar tremor, and weakness. The device would apply a counterforce to constrain the upper extremity to a force corridor, a region of force/velocity space, designed to increase movement accuracy. Execution of movements with counterforce assistance under certain conditions improves accuracy and should enable patients to develop enhanced strategies for dealing with the movement disorders resulting from their neurologic deficits. Generation of appropriate force feedback requires dynamic adjustment of feedback plant characteristics and integration of visuospatial information in a virtual reality environment. Sensory augmentation, including compensation for visual and proprioceptive loss, can theoretically also be achieved with this approach. The underlying principles in the development of such a system are presented.