The effect of masking noise on acoustic‐phonetic contrasts in post‐lingually deafened cochlear implant users

This study examined the effect on the vowel contrast distance (average inter‐vowel distance in the F1−F2 plane) of gradually decreasing the signal‐to‐noise ratio (SNR) in the auditory feedback of a post‐lingually deafened cochlear implant (CI) user at 1‐month and 1‐year following CI processor activation. Masking noise, mixed with normal levels of speech feedback, was presented through the headpiece of a research sound processor to the CI user. As a control, an analogous procedure was used for a normal‐hearing speaker where the masking noise and speech feedback were delivered over headphones. The SNR was gradually decreased over seven steps as the speakers produced ten repetitions of two vowel contrasts (æ\/[g\/] and i\/u). Speech SPL and vowel contrast distance were measured at all seven masking noise levels. Data from both subjects showed that SPL gradually increased with decreased SNR, while contrast distance decreased. The effect was greater after 1 year of experience with a CI than at 1 month. The effect in the NH speaker was similar to that noted in the CI user after 1 year of experience. Data from additional subjects will be analyzed and reported. [Work supported by NIH Grant No. R01 DC03007.]