Study of time-sequential signal processing of auditory nerves using a cochlear implant

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The purpose of the research is to investigate what degree of tiem-sequential signals can be discriminated by cochlear electrical stimulation and what kind of physiological and psychological feefcts by the electrimental results, time resolution obtained by the time-sequential electrical stimulation to the cochlea was found to be superior to that by auditory stimulation and a speech processing method that spectral patterns are converted into time-sequential signals was found to be effective for transmitting the speech information to the auditory nerves. Furthermore, from the result that tnnitus was suppressed by subthreshold electrical stimulation to the cochlea, an implantable tinnitus suppresser was designed and adopted to three patients with tinnitus. The following is summary of research results.(1)Time resolution was found to be about 150 us from the test of time-sequential electrical stimulation to the cochlea of the hearing impaired and one of pa ; tients could discriminate 5 vowels converted into time-sequential stimuli at 60% correct rate without training.(2)From the results of tinnitus suppression tests by more than 300 persons with tinnitus, it was found that tinnitus disappeared at 30 % of patients and tinnitus reduced at 63%.(3)From the measurements of SOUID, EEG and blood flow, it was assumed that parasympathetic nerves of autonomic nervous system became superior, and the brainstem and the limbic system became active. Although the purpose of the research was to investigate the signal processing mechanism of auditory nervous system, main results were obtained from tinnitus suppression tests. However, it is expected that a part of signal processing mechanisms will be clarfied by the long term use of implantable tinnitus suppressers. As the implantation technique was established and the biocompatibility of the device was porven, the research will be continued to find the optimal signal conversion method of speech signals.