Sensory Feedback System

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Functional Electrical Stimulation(FES) is very efficient for the restoration of the paralyzed upper extremities. Functional hand movements have been restored in C5-6 quadriplegic patients by the microcomputer based multi-channel FES system which we developed.Such patients are deprived of not only motor function but also sensory function. To restore the sensation relating to the FES-produced hand movements, we have studied the electrocutaneous stimulation methods. Such patients have skin sensation only in the upper part above the shoulders.(1)We investigated the basic characteristics of the shoulder skin sensation to the electrical stimulation on the following points ; absolute threshold and pain threshold as a function of stimulation and their dependence on the pulse repetion frequency, frequency resolution, spatial resolution, temporal resolution, etc..(2)We also investigated electrical "phantom sensation". Subject can feel the moving sense between the two pairs of the stimulation electrodes. An effective new method to produce the phantom image are proposed. The amplitude of the current pulse trains applied to two separate electrodes are modulated complementarily to each other ; one increases while the other decreases. The amount of modulation must be modified by the combination of two stimuli which gives subjects almost even sensation of the fused images. Qualitative and quantitative characteristics of the phantom sensation were revealed by this research project. In addition, widely moving phantom images could be produced by three channel arrangement. By these methods, analog quantities which reflect finger displacement or grasping pressure can be converted to smoothly moving phantom images with minimum number of electrodes.