The clinical trial of a multi-channel cochlear prosthesis

Abstract

The results of a multiple-electrode cochlear implant carried out on 1st August, 1978 on a totally deaf patient (post-lingual hearing loss) showed that he could perceive sounds of different pitches depending on the electrode stimulated, and this finding was consistent with the place theory of frequency coding. Furthermore, stimulating individual electrodes produced percepts which the patient described as vowel-like in quality. The patient could also perceive different pitches which varied with the rate of stimulation up to 200 pulses/second, but at higher rates he had difficulties perceiving pitch changes (Clark et al. 1978; Tong et al, 1979).

As a result of the psychophysical studies a speech processor was developed. The speech processor extracted: firstly, the voicing frequency to help the patient hear the rhythm of speech and know whether a speech sound was voiced or unvoiced (e.g., /b/ versus /p/); and, secondly, the second formant to enable the patient to recognize vowels and consonants and so hear words. In order to maximize speech intelligibility, the second formant stimulated an appropriate electrode, and the rate of stimulation on that electrode was related to the voicing frequency.