A COCHLEAR PROSTHESIS: FURTHER CLINICAL OBSERVATIONS; PRELIMINARY RESULTS OF PHYSIOLOGICAL STUDIES

Abstract

A series of simple psychoacoustic studies were conducted on three deaf patients with indwelling scala tympani electrodes to determine better what they hear as a consequence of electrical stimulation. Physiological experiments on cats implanted with a similar electrode were conducted to determine how the sensation heard by these patients is generated and encoded in the auditory nervous system. Some preliminary results of these animal experiments are described. Additional improvements in the surgical implantation procedure are detailed. Results of these studies suggest the following: 1. long-term intracochlear implantation is technically feasible without unusual complications; 2. mechanical stability of the implant prosthesis has been improved by fixing the implant to the temporal bone with methyl methacrylate cement; 3. with simple periodic electrical stimuli the implanted patients described tonal sensation for frequencies ranging from about 100 Hz to more than 10 kHz; 4. apparent pitch changes rapidly as a function of stimulus frequency at frequencies below about 500 Hz; 5. subjects are able to identify many common environmental sounds and a few words, but conventional speech discrimination is poor; 6. the sound sensation generated by electrical stimulation arises as a consequence of simultaneous excitation of a broad segment of the acoustic nerve; therefore, no “place” coding of the electrical stimuli occurs in the cochlea; 7. if no cochlear place coding occurs then tonal quality ascribed to sounds heard with electrical stimulation at low stimulus frequencies must be encoded by the temporal ordering of discharges in stimulated neurons.