A Study on Utility and improvement of Sensory Substitute Devices for Education Engineering of the Hearing Impaired.

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1. A new display method of vibration patterns was proposed in order to improve the recognition of consonants by our fingertip tactile vocoder for the deaf.(1) One of the reasons why consonant parts could not be so much recognized as vowels was found to be caused by temporal masking based on psychophysical experiments. To solve the above problem, the speech spectrum patterns were displayed on a fingertip with swept mode using a small vibrator matrix with 16 rows.(2) Two-point thresholds were measured in the various conditions while sweeping two vibrating points on a fingertip. The optimal swept speed was obtained from the experiments. It was ascertained that the temporal masking of consonant parts by vowels could be avoided by using the optimal swept speed.2. A new model of an extracochlear prosthesis has been designed for deaf infants and children.(1) We have developed a Pt-Ir electrode coated with polyvinyl alcohol gel which contains a saline solution. The coated electrode is suitable for the extracochlear prosthesis because it can firmly adhere to the round window membrane without causing damage so that the residual hearing of patients may not be lost.(2) In our telemetry method, the output of the speech processor is transmitted with electromagnetic coupling from the first coil inside the earmold to the second coil implanted under the skin of an external ear. Using this method, the subject only has to receive a very minor operation. Our cochlear prosthesis may possibly be applied to even a small child.(3) As a speech coding method. a new idea has been proposed to simultaneously transmit the pitch signal and the second formant frequency through an electrode. It took about 20 ms to detect the pitch signal and the second formant frequency by using a digital signal processor. This new method of speech coding has proven effective for discrimination of the five Japanese vowels based on simple tests.