Biomedical Engineering Study on a Design of Cochlear Implants.

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A purpose of this research is to do fundamental experiments regarding an optimal design of the cochlear implant that electrically stimulates the survival auditory nerves for the deaf. Researches carried out are the following 4 points.(1)It was investigated what kind of current distribution produces inside the cochlea of a human cadaver when electrodes were inserted into the cochlea. (2) A spwwch processor was developed on the basis of the above result and the discrimination ability of synthetic vowels was evaluated by a subject implanted with an eight channel cochlear prosthesis. (3) A new model of the electrode for the extracochlear implant was developed as a less invasive alternative to electrode insertion in the cochlea. (4) Such a speech coding method that discrimination of vowels is possible with single channel method was proposed and its efficacy was evaluated by an animal experiment.As results, (1) a stimulation current path from the inside of the cochlea to the outside wlarifie … More d. It is found out that a stimulation current spreads largely outside the cochlea (T.Ifukube, 1987a). (2) A speech processor that had a function of lateral inhibition was designed in order to compensate for the wide current spread and its efficacy was confirmed by a recognition experiment of synthesis vowels (T.Ifukube, 1987b). (3)A Pt-Ir wire electrode covered with Polyvinyl alcohol gel including saline solution was developed as a stimulation electrode for a single channel extracochlear implant. The electrical characteristics of the electrode was checked and it was ascertained that the electrode had almost the same characteristics as human body (T.Ifukube, et al, 1988, J.Matsushima et al, 1988). (4) the speech processor for a single channel cochlear implant was designed which produced a time sequential stimulation pulses obtained by combining pitch signals and the second formant frequency of voices. The efficacy of this coding method was proved from a view point of compound action potential responded to stimulation that gave to the cochlea of guinea pig (T.Ifukube et al, 1988, K.Takahashi et al, 1988). Less