Objective: Auditory perception is essential for speech and language development, emphasizing the significant impact of hearing loss on social and occupational communication. Although cochlear implants (CI) address postlingual hearing loss in adults, the restored auditory feedback may be insufficient for precise vocal adjustments and laryngeal muscle coordination. The interaction between auditory and motor inputs plays a key role in sensory-motor coupling for speech production. "Auditory feedback," the real-time and delayed perception of speech sounds, allows for correction of errors in rhythm, prosody, and voice quality. Voice Onset Time (VOT) serves as an acoustic indicator of motor coordination by distinguishing voicing nuances. It offers unique insights into fine coordination of vocal fold movements of speech production, making it a valuable tool for analyzing phonetic distinctions. This study aims to address the gap in assessing VOT to capture subtle speech variations in CI users during a continuous speech task.
Method: Recordings of CAPE-V sentences were collected from 25 cochlear implant (CI) users and 25 healthy speakers, with a mean age of 33.2 years (SD = 11.5, age range 18–55). Ten words containing both voiced and voiceless consonants were selected from the CAPE-V sentences. Voice Onset Time (VOT) measurements for stop consonants at the beginning of these words were analyzed using PRAAT. An independent sample t-test was performed to compare the two groups, matched by age and gender. Additionally, ANCOVA was used to assess the impact of demographic factors on VOT values in the CI group.
Results:The healthy speakers showed higher VOT values for the unvoiced consonant /p/ in the syllables /po/,/p_/,/pe/, and /pa/, whereas the CI group had higher VOT values for the voiced consonant /d/ in the syllables /da/ and /di/ (P < 0.05). Apart from the /po/ and /di/ syllables, demographic factors had no significant influence on VOT values (P ≥ 0.8).
Conclusion: Despite improvements in speech quality after CI, subtle differences persist. VOT is affected by various linguistic factors, including articulatory position, vowel context. Other influences on VOT measurements include the articulatory features of consonants, coarticulation effects, and the position of words within sentences. Additionally, variations in aerodynamic conditions and temporal adjustments during the TVC movement, influenced by the structural and functional distinctions of the larynx and respiratory subsystem, contribute to these subtle differences. While CI facilitates phoneme distinction in syllables, ongoing articulation challenges in adults underscore the necessity for targeted training in rehabilitation programs to further enhance speech clarity and improve the quality of CI user.