Biomechanical Models to Represent Vocal Physiology: A Systematic Review

As the primary means of communication, voice plays an important role in daily life. Voice also conveys personal information such as social status, personal traits, and the emotional state of the speaker. Mechanically, voice production involves complex fluid-structure interaction within the glottis and its control by laryngeal muscle activation. An important goal of voice research is to establish a causal theory linking voice physiology and biomechanics to how speakers use and control voice to communicate meaning and personal information. Establishing such a causal theory has important implications for clinical voice management, voice training, and many speech technology applications. This paper provides a review of voice physiology and biomechanics, the physics of vocal fold vibration and sound production, and laryngeal muscular control of the fundamental frequency of voice, vocal intensity, and voice quality. Current efforts to develop mechanical and computational models of voice production are also critically reviewed. Finally, issues and future challenges in developing a causal theory of voice production and perception are discussed.

A simple, low-dimensional model of the body-cover vocal-fold structure is proposed as a research tool to study both normal and pathological vocal-fold vibration. It maintains the simplicity of a two-mass model but allows for physiologically relevant adjustments and separate vibration of the body and the cover. The classic two-mass model of the vocal folds [K. Ishizaka and J. L. Flanagan, Bell Syst. Tech. J. 51, 1233-1268 (1972)] has been extended to a three-mass model in order to more realistically represent the body-cover vocal-fold structure [M. Hirano, Folia Phoniar. 26, 89-94 (1974)]. The model consists of two "cover" masses coupled laterally to a "body" mass by nonlinear springs and viscous damping elements. The body mass, which represents muscle tissue, is further coupled laterally to a rigid wall (assumed to represent the thyroid cartilage) by a nonlinear spring and a damping element. The two cover springs are intended to represent the elastic properties of the epithelium and the lamina propria while the body spring simulates the tension produced by contraction of the thyroarytenoid muscle. Thus contractions of the cricothyroid and thyroarytenoid muscles are incorporated in the values used for the stiffness parameters of the body and cover springs. Additionally, the two cover masses are coupled to each other through a linear spring which can represent vertical mucosal wave propagation. Simulations show reasonable similarity to observed vocal-fold motion, measured vertical phase difference, and mucosal wave velocity, as well as experimentally obtained intraglottal pressure.