DEVELOPMENT OF A NEXT GENERATION OF AN ARTIFICIAL EXTREMITY SYSTEM CAPABLE OF GENERATING AND GIVING ARTIFICIAL SENSATIONS TO SUBJECTS WITH HIGH-GRADE REALITY

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The goal or this project was to develop an artificial arm system capable of sensing mechanical stimuli and then transferring these stimuli to the subject so that the subject experiences the stimuli as the corresponding somatic sensations. The technique we used consisted of electrically stimulating sensory nerve fibers, each of which innervates a single mechanoreceptor units, in accordance with the output of the sensors on the artificial arm.A tungsten microelectrode was inserted percutaneously into the median nerve, and fixed at a point where the activities of a single SA mechanoreceptor unit could be recorded. Electrical microstimulation was then performed with the same microelectrode using square-wave pulses of 250 μsec duration. The amplitude and the frequency of the stimulation pulses were altered in various ways, and qualitative and quantitative relationship between the properties of the micro-electrical stimulation and the intensities and areas of the evoked pressure sensations w … More ere studied. In this trials, the subjective intensities of the evoked pressure sensation were evaluated quantitatively by means of psychophysical methods (such as method of limits, method of adjustment, or up-and-down method.In order for this technique to be acceptable for actual clinical use, it is necessary to stimulate both a large number and various kinds of nerve fibers simultaneously. We investigated also how an evoked sensation and its projected area are affected when electrical stimulation is given simultaneously to multiple sensory nerve fibers each of which separately innervate different single mechanoreceptor unit.As a result, the subjective magnitude of the evoked pressure sensation was appeared to be related to a positive power of the frequency ; however, there was essentially no change in the amplitude of the electrical stimulation. The projected area was affected neither by the amplitude nor the frequency. With regard to simultaneous stimulation of multiple sensory nerve fibers, results so far indicated that the sensation evoked when two mechanoreceptor units underwent simultaneous electrical stimulation became a simple addition concerning the projected areas, kinds of sensation, and the magnitude, respectively, and no "non-linear" phenomena took place.According to these results, we developed a prototype of an artificial arm system using the same technique as stated above. A robot hand system (with the shape of a human hand) was used as an artificial arm system ; its fingers and palm was covered with a sheet of pressure-conductive rubber over the area corresponding to the projected area of the subject's hand (i.e. the area over which the single mechanoreceptor unit produces a sensation). Pressure was then applied to the pressure-conductive rubber ; a microcomputer used the output voltage of the pressure-conductive rubber to determine the frequency of the electrical pulses for stimulating the sensory nerve fiber, and these electrical pulses were then output to the sensory nerve fiber via the tungsten microelectrode. The subjective intensities of the sensations evoked by the stimulation were described by the subjects using a slide volume, etc. ; these subjective evaluations and their changes with respect to time were compared with the strengths of the stimuli applied to the pressure-conductive rubber of the robot hand.The system worked in a satisfactory manner, and the subjects could feel the pressure sensation at the corresponding area resulting from the pressure that was applied to the pressure conductive-rubber of the robot hand. There was also a good correlation between the pressure applied to the pressure-conductive rubber and the subjective intensities of the evoked sensations. Less