The impact of bimodal hearing on speech acoustics of vowel production in adult cochlear implant users

Purpose: This study aimed to investigate the acoustic changes in vowel pro-duction with different forms of auditory feedback via cochlear implant (CI), hear-ing aid (HA), and bimodal hearing (CI + HA). Method: Ten post–lingually deaf adult bimodal CI users (aged 50–78 years) pro-duced 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 [F1], second formant frequency [F2], and vowel space area) and suprasegmental features (duration, intensity, and fundamental frequency [fo]) 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: F1s of all vowels decreased; F2s of front vowels but not back vowels increased; vowel space areas increased; and vowel durations, intensities, and fos decreased with statistical significance in the HA, CI, and CI + HA conditions relative to the ND condition. Only fos were lower, and vowel space areas were larger with CI and CI + HA than with HA. Average changes in fo, intensity, and F1 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 fo and F1 with the use of hearing devices may be largely driven by changes in intensity.