The cochlear implant: Basic principles

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Abstract
In recent years the cochlear implant has been a subject of much discussion and controversy. The clinician has often been confused by the conflicting reports of success and failure. In this paper the development of the cochlear implant is reviewed and its present status summarized. It is hoped that the clinician may thereby gain an understanding of this device so that he can better evaluate its present and future status. Selection of Patients for Cochlear Implantation. The cochlear implant will benefit only those patients with hair cell loss who have remaining viable auditory neurons. In order to determine whether viable neurons remain, an electric current is passed through a small needle which is placed onto the promontory through the tympanic membrane. If patients experience an auditory sensation as a result of this electrical stimulation, it is felt that they are suitable candidates for a cochlear implant. Feasibility of Long-Term VIIIth Nerve Stimulation. Information Transfer by Electrical Stimulation. Single-channel stimulation produces only periodicity pitch, and information transfer is insufficient for speech discrimination. Present Status of the Cochlear Implant. To the present time 15 patients have been implanted with a unipolar electrode under the direction of the Ear Research Institute. These patients have all benefited from their devices. They are able to perceive background sounds and receive a cadence or rhythm to speech which makes the device helpful in lipreading. None of the patients have developed significant speech discrimination. Future of the Cochlear Implant. It is our opinion that the present single-channel cochlear implant is a clinically useful device. Work is continuing on the thorough evaluation and rehabilitation of patients with this device. Development of a multiple-channel electrode and stimulator is the goal of several groups active in the cochlear implant field. The theoretical model for the future cochlear implant is an eight or more channel device with each electrode stimulating a different population of nerve fibers. The stimulator will separate the incoming signal into eight or more frequency bands and then differentially stimulate the separate electrodes with a coded signal. It is hoped that sufficient information may thereby be provided for understanding of speech. Preliminary studies give hope that this may be possible.

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