Analysis of vibratory mode changes in symmetric and asymmetric activation of the canine larynx

Abstract

Investigations of neuromuscular control of voice production have primarily focused on the roles of muscle activation levels, posture, and stiffness at phonation onset. However, little work has been done investigating the stability of the phonation process in regards to spontaneous changes in vibratory mode of vocal fold oscillation as a function of neuromuscular activation. We evaluated 320 phonatory conditions representing combinations of superior and recurrent laryngeal nerve (SLN and RLN) activations in an in vivo canine model of phonation. At each combination of neuromuscular input, airflow was increased linearly to reach phonation onset and beyond from 300 to 1400 mL/s. High-speed video and acoustic data were recorded during phonation, and spectrograms and glottal-area-based parameters were calculated. Vibratory mode changes were detected based on sudden increases or drops of local fundamental frequency. Mode changes occurred only when SLNs were concurrently stimulated and were more frequent for higher, less asymmetric RLN stimulation. A slight increase in amplitude and cycle length perturbation usually preceded the changes in the vibratory mode. However, no inherent differences between signals with mode changes and signals without were found.

Reconstruction of Vocal Fold Medial Surface 3D Trajectories: Effects of Neuromuscular Stimulation and Airflow

“…As discussed, the observed F0 drops after phonation onset may be in part an artifact of the hemilarynx‐model and subglottal resonances. A similar effect could also explain the only minor increase of F0 of up to 12 Hz with increasing flow while an increase of over 15 Hz would have been expected for conditions without SLN stimulation 12,26 . This has to be investigated in further studies.…”

“…In these conditions, only a faster superior oscillation was induced before full VF oscillation ensued. This is surprising as previously SLN activation was thought to be required for these kinds of mode changes 26 …”

“…This is surprising as previously SLN activation was thought to be required for these kinds of mode changes. 26 The observed mode changes briefly after onset in this work may be explainable due to a combination of multiple factors: the gradually increasing flow, lower SLN stimulation, and the VF resting against the glass surface. Additionally, subglottal resonances may have affected onset.…”

“…A similar effect could also explain the only minor increase of F0 of up to 12 Hz with increasing flow while an increase of over 15 Hz would have been expected for conditions without SLN stimulation. 12,26 This has to be investigated in further studies. As we work with a hemilarynx model, laryngeal nerves are only stimulated one-sided, and the distance between VF and the glass prism might have been slightly too high.…”