Speech Encoding Scheme for the Extra-Cochlear Pulsed Electrical Stimulation System

An extra-cochlear stimulation system has been investigated as a less invasive alternative to conventional cochlear implant; however, the system is used primarily as a speech-reading aid. The purpose of this study was to develop a speech encoding scheme for the extra-cochlear stimulation system to convey intelligible speech. A click-modulated speech sound (CMS) was created as a simulation of the extra-cochlear stimulation system. The CMS is a repetitive click with a repetition rate similar to the formant frequency transition of an original sound. Seven native Japanese speakers with normal hearing participated in the experiment. After listening to the CMS, synthesized from low familiarity Japanese words, the subjects reported their perceptions. The results showed that the rates of correctly identified vowels and consonants were significantly higher than those of the control stimulus, suggesting that the CMS can generate at least partially intelligible vowel and consonant perceptions. In all, the speech encoding scheme could be applied to the extra-cochlear stimulation system to restore speech perception.