Research into the development of a wearable cochlear prosthesis has been ongoing at the House Ear Institute since 1960. Several different signal processing schemes and electrode arrays have been tried. Presently, the patients use a wearable signal processor in which the analog of the acoustic signal amplitude modulates at 16 kHz carrier wave; the modulated signal is electrically transduced across the skin via a pair of induction coils. The implanted induction coil terminates at a single active electrode placed 6 to IS mm into the scala tympani and a return electrode placed in the 'eustachian tube or temporalis muscle (Danley amd Fretz, 1982; House, 1982).
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