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Magnetoresistive eye and head velocity and position detector


, : Magnetoresistive eye and head velocity and position detector. Society for Neuroscience Abstracts 26(1-2): Abstract No -744 1

A method to measure 3D eye movements (head relative) and head orientation in space has been developed. The system is small and head mounted, allowing for telemetry of a freely moving subject. All obstacles can be removed from the subject's visual field. The system consists of magnetoresistive (MR) sensors, silicon (MEMS) accelerometers, and low power amplifiers. Mounted on the eye(s) is a ring of plastic with embedded extremely small (<1mm in length) high strength magnets. MR field angle detectors that measure in the microgauss range mounted above and lateral to the orbit measure the ring orientation . These sensors cover a range of +/-90 degree with a resolution of 0.07 degrees. Combining the Earth's magnetic field signals from three head mounted MR sensors and two gravity driven (head mounted) accelerometers with these signals, a computer can calculate in real time, velocity and position of both head and eyes. The system can compensate for static ferrous metal objects in the room with proper calibration, but significant changes in the Earth's magnetic field or dynamic local disturbances are beyond the capabilities of the present system. The current system handles rotational movement measurements and is easy to build at low cost. For a freely moving subject, the system would require more accurate amplifiers and periodic calibration to compensate for offsets from the double integration of acceleration to position. Ultimately it will allow us to record from implanted electrodes in a freely moving subject and receive high resolution head, and eye in head, orientation data as well as neuronal unit, EMG or other physiological signals by telemetry.

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