Speech Encoding Scheme for The Extra-cochlear Laser Stimulation System

Cochlear implants were widely used for hearing impaired, while at the same time the devices require surgical intervention for implanting. Infrared laser neural stimulation has been investigated for overcoming the drawback because the laser can elicit neural activity without contacting tissues. The purpose of this study was to develop a speech encoding scheme for the infrared laser auditory prosthesis. A click-modulated speech sound (CMS), which is a click train with a repetition rate of formant frequencies of an original speech sound, was created as an acoustic simulation of the laser auditory prosthesis. Four Japanese speakers with normal hearing participated in the experiment. Subjects reported their perceptions of the CMS synthesized from low familiarity Japanese words. As a result, CMS replicating first and second formant frequencies created statistically significant vowel and consonant perception. The result suggests that laser auditory prosthesis replicating formant frequencies could restore the speech perception.