The Impact of Bimodal Hearing on Speech Acoustics of Vowel Production in Adult Cochlear Implant Users

Abstract

Purpose: This study aimed to investigate the acoustic changes in vowel production with different forms of auditory feedback via cochlear implant (CI), hearing aid (HA), and bimodal hearing (CI + HA). Method: Ten post–lingually deaf adult bimodal CI users (aged 50–78 years) produced English vowels /i/, /ɛ/, /æ/, /ɑ/, /ʊ/, and /u/ in the context of /hVd/ during short-term use of no device (ND), HA, CI, and CI + HA. Segmental features (first formant frequency [ F 1 ], second formant frequency [ F 2 ], and vowel space area) and suprasegmental features (duration, intensity, and fundamental frequency [ f o ]) of vowel production were analyzed. Participants also categorized a vowel continuum synthesized from their own productions of /ɛ/ and /æ/ using HA, CI, and CI + HA. Results: F 1 s of all vowels decreased; F 2 s of front vowels but not back vowels increased; vowel space areas increased; and vowel durations, intensities, and f o s decreased with statistical significance in the HA, CI, and CI + HA conditions relative to the ND condition. Only f o s were lower, and vowel space areas were larger with CI and CI + HA than with HA. Average changes in f o , intensity, and F 1 from the ND condition to the HA, CI, and CI + HA conditions were positively correlated. Most participants did not show a typical psychometric function for vowel categorization, and thus, the relationship between vowel categorization and production was not tested. Conclusions: The results suggest that acoustic, electric, and bimodal hearing have a measurable impact on vowel acoustics of post–lingually deaf adults when their hearing devices are turned on and off temporarily. Also, changes in f o and F 1 with the use of hearing devices may be largely driven by changes in intensity.