Vocal control and speech production in cochlear implant listeners: A review within auditory-motor processing framework

A comprehensive literature review is conducted to summarize and discuss prior findings on how cochlear implants (CI) affect the users’ abilities to produce and control vocal and articulatory movements within the auditory-motor integration framework of speech. Patterns of speech production pre- versus post-implantation, post-implantation adjustments, deviations from the typical ranges of speakers with normal hearing (NH), the effects of switching the CI on and off, as well as the impact of altered auditory feedback on vocal and articulatory speech control are discussed. Overall, findings indicate that CIs enhance the vocal and articulatory control aspects of speech production at both segmental and suprasegmental levels. While many CI users achieve speech quality comparable to NH individuals, some features still deviate in a group of CI users even years post-implantation. More specifically, contracted vowel space, increased vocal jitter and shimmer, longer phoneme and utterance durations, shorter voice onset time, decreased contrast in fricative production, limited prosodic patterns, and reduced intelligibility have been reported in subgroups of CI users compared to NH individuals. Significant individual variations among CI users have been observed in both the pace of speech production adjustments and long-term speech outcomes. Few controlled studies have explored how the implantation age and the duration of CI use influence speech features, leaving substantial gaps in our understanding about the effects of spectral resolution, auditory rehabilitation, and individual auditory-motor processing abilities on vocal and articulatory speech outcomes in CI users. Future studies under the auditory-motor integration framework are warranted to determine how suboptimal CI auditory feedback impacts auditory-motor processing and precise vocal and articulatory control in CI users.