Combination and comparison of electric stimulation and residual hearing

Abstract

Speech processing for cochlear implant users has now reached a level where some severely hearing-impaired hearing aid users may be better aided by a cochlear implant, or a hearing aid and implant together. This paper reviews studies comparing the loudness, pitch, and vowel perception in opposite ears of adults using cochlear implants and hearing aids. A study of nine subjects showed narrow dynamic ranges and steep loudness growth in both ears. Mismatches in aided thresholds and dynamic ranges at different frequencies resulted in highly variable loudness differences between the ears for some subjects. A comparison using pure tones showed that the electric pitch depended on both rate and electrode site. Pitch of electrodes was lower than expected from the characteristic frequency distribution in a normal cochlea. Synthetic vowels were used to show that signals presented via the implant and hearing aid may be perceived as different vowels in the two ears.