Neurophysiological Muscle Activation Scheme for Controlling Vocal Fold Models

Abstract

A physiologically-based scheme that incorporates inherent neurological fluctuations in the activation of intrinsic laryngeal muscles into a lumped-element vocal fold model is proposed. Herein, muscles are activated through a combination of neural firing rate and recruitment of additional motor units, both of which have stochastic components. The mathematical framework and underlying physiological assumptions are described, and the effects of the fluctuations are tested via a parametric analysis using a body-cover model of the vocal folds for steady-state sustained vowels. The inherent muscle activation fluctuations have a bandwidth that varies with the firing rate, yielding both low and high frequency components. When applying the proposed fluctuation scheme to the voice production model, changes in the dynamics of the system can be observed, ranging from fluctuations in the fundamental frequency to unstable behavior near bifurcation regions. The resulting coefficient of variation of the model parameters is not uniform with muscle activation. The stochastic components of muscle activation influence both the fine structure variability and the ability to achieve a target value for pitch control. These components can have a significant impact on the vocal fold parameters, as well as the outputs of the voice

Triangular body-cover model of the vocal folds with coordinated activation of the five intrinsic laryngeal muscles

“…Note that the proposed scheme for the TBCM model continues to be an approximation and has limitations that could be addressed in future studies, such as constraints for cartilage displacements (Geng et al, 2020;Hunter et al, 2004), superior-inferior accommodation of the larynx during phonation (Moisik and Gick, 2017), medial bulging and anterior-posterior gradient, among others. Other future avenues for exploration include the connection with a neurophysiological muscle activation that incorporates natural neurological fluctuations in the activation of intrinsic laryngeal muscles (Manriquez et al, 2019), and simulations of /VCV/ gestures to compute relative fundamental frequency.…”

“…These high order models can capture the complex biomechanical and geometrical changes of muscle activation but are likely too computationally demanding to account for neural motor control effects. Low order models can better handle the latter task (Manriquez et al, 2019) and are more suitable for comprehensive parametric simulations that would be needed in the context of laryngeal motor control. However, there is currently no muscle activation framework for low order models that incorporates the possibility of independent co-contraction of agonist/antagonist muscle pairs.…”

Asymmetric triangular body-cover model of the VFs with bilateral intrinsic muscle activation

“…While numerical models have traditionally been employed to simulate physiological mechanisms in modal and typical phonation, ongoing refinements have expanded their applicability to variables describing vocal function in pathological contexts. Modeling of vocal function provides a platform for exploring biomechanical aspects of impaired phonation, including the identification of biomechanical parameters and alterations in certain vocal pathologies (Jiang et al ., 2006; Samlan and Story, 2017; Tao and Jiang, 2007), VF geometrical properties (Lucero et al ., 2019; Mattheus and Brucker, 2011; Smith et al ., 2013), variations in intrinsic muscular control of the larynx (Chhetri et al ., 2009; Manríquez et al ., 2019), and changes in the aeromechanical-acoustic interaction (Erath et al ., 2019; Story, 2002; Zhang, 2018).…”

LaDIVA: A neurocomputational model providing laryngeal motor control for speech acquisition and production

“…The neural motor control and biomechanical mechanisms of typical and disordered laryngeal function involved in vocal production, and the interaction between them are poorly understood, partly due to the invasive nature of assessment and characterization of laryngeal function (i.e., laryngeal electromyography: [ 34 – 39 ], laryngeal endoscopy: [ 40 , 41 ], contact pressure probes:[ 42 ]). The geometry and mechanical properties of the vocal folds (VFs) exhibit a great deal of variability as a function of intrinsic muscle activation, voicing conditions, sex, age, and individual anatomical features, and complex physical interactions occur between VF tissue, airflow, and sound [ 43 , 44 ]. Thus, it is crucial to investigate these components and their variability to better understand laryngeal function in typical and pathologic conditions.…”