The Effect of Bimodal Hearing on Speech Intonation Production in Adult Cochlear Implant Users

Prosodic features such as fundamental frequency (F0), intensity, and duration convey important information of speech intonation (i.e., is it a statement or a question?). Because cochlear implants (CIs) do not adequately encode pitch-related F0 cues, pre-lignually deaf pediatric CI users have poorer speech intonation perception and production than normal-hearing (NH) children. In contrast, post-lingually deaf adult CI users have developed speech production skills via normal hearing before deafness and implantation. Further, combined electric hearing (via CI) and acoustic hearing (via hearing aid, HA) may improve CI users’ perception of pitch cues in speech intonation. Therefore, this study tested (1) whether post-lingually deaf adult CI users have similar speech intonation production to NH adults and (2) whether their speech intonation production improves with auditory feedback via CI+HA (i.e., bimodal hearing). Eight post-lingually deaf adult bimodal CI users and nine NH adults participated in this study. 10 question-and-answer dialogues with an experimenter were used to elicit 10 pairs of syntactically matched questions and statements from each participant. Bimodal CI users were tested under four hearing conditions: no-device (ND), HA, CI, and CI+HA. F0 change, intensity change, and duration ratio between the last two syllables of each utterance were analyzed to evaluate the quality of speech intonation production. The results showed no significant differences between CI and NH participants in any of the acoustic features of questions and statements. For CI participants, the CI+HA condition led to significantly greater F0 decreases of statements than the ND condition, while the ND condition led to significantly greater duration ratios of questions and statements. These results suggest that bimodal CI users change the use of prosodic cues for speech intonation production in different hearing conditions and access to auditory feedback via CI+HA may improve their voice pitch control to produce more salient statement intonation contours.