Cochlear Implant Listeners Perception of Temporal and Spectral Voicing Cues
Objectives: Perception of voice onset time (VOT) is often used as an index of auditory temporal processing. However, some VOT stimuli are less appropriate for this goal because of the vowel that follows the consonant. For example, there are complementary frequency cues for the low vowel /ɑ/, but not for the high vowel /i/, meaning choice of vowel context affects studies on timing perception. For people who use cochlear implants who have residual aidable hearing, perception of those frequency cues could be a key benefit, but could also pose a problem for researchers who are looking to determine the ability to perceive timing cues. We hypothesize that VOT perception will be better when the following vowel is /ɑ/, because it contains both temporal and spectral cues for voicing, whereas /i/ provides only temporal cues. We further hypothesize that low-frequency hearing will enable listeners to exploit that benefit when the signal is degraded.
Design: Listeners with cochlear implants or with normal hearing completed a task in which they categorized words varying by VOT between /d/ and /t/, where vowel formant transitions naturally covaried with VOT duration. The following vowel was either /ɑ/, which allowed perception of spectral contours, or /i/ which did not. The onset consonant of each word was categorized as voiced or voiceless and modeled using a binomial statistical model that included VOT, vowel and hearing as fixed main and interacting effects.
Results: Both listener groups reliably categorized voicing contrasts. Performance was better in the /ɑ/ context, suggesting use of spectral cues. When adding low-frequency cues to a degraded signal, voicing perception was improved when the vowel was /ɑ/ but much less when the vowel was /i/, likely due to differences in the availability of formant transitions.
Conclusions: Spectral cues in vowels can play a role in perceiving voice onset time. Vowels that contain formant contours can create a confounding variable when studying VOT perception. Perception of formant transitions can interfere with measuring auditory temporal perception but could potentially be useful for measuring the benefit of residual low-frequency hearing.
Abstract focus: Cochlear Implants, Speech Perception
Biographical sketch of the presenter: Lexi Olson is an undergraduate student at the University of Minnesota–Twin Cities studying Speech-Hearing-Language Sciences. She is a member of Matthew Winn’s Listen Lab which focuses on studying speech perception and listening effort in people with cochlear implants.
Learner outcomes: After this presentation, the audience will be able to identify the confounding variables that vowels can have when conducting experiments related to VOT and perception of timing cues. Conflict of Interest Statements for ALL authors The authors declare no conflicts of interest.