Using Haptic Feedback to Improve Grasp Force Control in Multiple Sclerosis Patients

We describe a simple and low-cost system that can help multiple sclerosis (MS) patients with asymmetric impairment to exert better grasp force control in manipulation tasks. The approach consists of measuring force vectors at the fingertips of the impaired hand, computing the force imbalance among the fingers, and providing corresponding haptic signals to the fingers of the opposite hand. Tests conducted on 24 MS patients indicated that for those with mild impairment, slightly better results were obtained with an ldquoevent-cuerdquo feedback (ECF) that alerted them when the grasp forces were straying outside of a desirable range. For patients with more severe impairment, better results were obtained by providing a proportional signal, in which the frequency and duty cycle of vibration pulses were correlated directly with the magnitudes of the fingertip forces. Post-test surveys of the patients also indicated that mildly impaired subjects preferred an event-cue feedback, and more severely impaired subjects preferred the proportional feedback.