The goal of this project is to develop a clearer understanding of how structural and vibratory asymmetry of the vocal folds affects both clinical measures of vocal function and severity ratings of dysphonia. Such asymmetries are key features underlying many voice disorders, including unilateral vocal fold motion impairment (VFMI), and likely contribute to the perception of breathy voice quality. Clinical voice evaluation and management are based in understanding how vocal fold vibration patterns are related to vocal function measures and perception. Determining how specific asymmetries contribute to the vocal output, however, is limited in human subjects by difficulty imaging the three-dimensional movement characteristics of vocal fold vibration, inability to systematically vary individual components of vibration, and challenges of separating the glottal source (i.e., vocal fold vibration) from filter (i.e., vocal tract) characteristics of aerodynamic and acoustic signals. Delineating these causal relationships can immediately impact the clinical use and interpretation of vocal function measures and treatment decisions for patients with breathy voice secondary to VFMI. The approach for this research is to use a kinematic model of vocal fold vibration that will allow for differential left/right control of vocal fold adduction, medial surface bulging, vibratory nodal point, phase, and fundamental frequency. The vocal fold model will be coupled to a comprehensive model of speech production, with which glottal area, vocal fold contact area, glottal airflow and output pressure can be simulated as if they were produced by a human talker. The inclusion of a trachea and vocal tract in the system allows for additional testing of the effect of airspace on the resulting output signals. For this project, the vocal fold structure and vibratory parameters selected for systematic modification will be consistent with changes reported in VFMI, and vocal fold and vocal tract changes occurring with surgical and behavioral management will be tested. The research will be guided by three hypotheses: 1) the effects of structural and vibratory asymmetry of the vocal folds can be characterized with a set of clinically-feasible acoustic and aerodynamic measures of vocal function, 2) the degree of structural and vibratory asymmetry will be directly related to severity ratings of dysphonia, and 3) constriction of the epilaryngeal section of the supraglottal vocal tract will decrease the degree of dysphonia registered both by vocal function measures and perceptually-based severity ratings.
Three specific aims are designed to address these hypotheses: 1) To generate a database of simulated signals based on 47 combinations of asymmetric settings for vocal fold adduction, medial surface bulging, vibratory nodal point, phase, and fundamental frequency. The simulations will be repeated for the vowels /a/, /i/, /u/, and /ae/ and for a constricted epilarynx. 2) To measure, from each collection of signals generated in Aim 1, a battery of clinically-feasible kinematic, aerodynamic, and acoustic measures. 3) To conduct perceptual experiments that assess the severity of the dysphonia represented by the signals generated in Aim 1.
Vocal fold motion impairment with asymmetric vocal fold vibration leads to a breathy, weak voice, which is undesirable for people in many professions such as teaching, law enforcement, clergy, medicine, or the military. Breathy voice caused by asymmetric vocal fold vibration becomes a public health concern when it interferes with an individual's ability to communicate at work and leads to withdrawal from social situations. Better understanding of the how specific asymmetries contribute to voice quality will lead to more efficient evaluation and treatment.
|Samlan, Robin A; Story, Brad H; Lotto, Andrew J et al. (2014) Acoustic and perceptual effects of left-right laryngeal asymmetries based on computational modeling. J Speech Lang Hear Res 57:1619-37|
|Samlan, Robin A; Story, Brad H; Bunton, Kate (2013) Relation of perceived breathiness to laryngeal kinematics and acoustic measures based on computational modeling. J Speech Lang Hear Res 56:1209-23|