Objective: Vocal registers are often described in terms of perceptual evaluation, acoustics, aerodynamics, and videoendoscopic imaging of vocal fold vibration. While the medial surface thickness has long been hypothesized to play an important role in regulating vocal registers, differences in medial surface vibration pattern between registers have yet to be experimentally investigated, due to challenges in visualizing the medial surface in vivo. The goal of this study is to image and compare medial surface vibration patterns between vocal fry, chest, head, and whistle registers, using optical coherence tomography (OCT).

Methods/Design: An experienced classically trained singer produced sustained vowel /i/ in different pitch and registers, including vocal fry, chest, head, and whistle. For each condition, vocal fold vibration in the coronal plane was imaged using a transoral, swept-source rigid laryngoscope equipped with optical coherence tomography (OCT) technology. The produced speech sound and electroglottographic data were also recorded. The vocal fold vibration velocity and trajectory were calculated using the digital image correlation method. Vibratory measures were also extracted, including closed quotient, medial surface vertical thickness, vertical displacement, mucosal peak, and amplitude of lateral excursion.

Results/Conclusions: The vocal fold medial surface was generally thicker and exhibited larger vibration amplitude and vertical phase difference in chest voices than in head voices. Vocal fold vibration of small amplitude was observed in whistle voices, indicating that a similar mechanism of flow-induced vibration as in chest voices may be involved in the whistle register. The results demonstrate the potential of OCT in identifying and monitoring changes in laryngeal mechanisms in both normal and pathological voices.