Date: Wed, May 10, 16:00-17:30
Venue: Room M203, Komaba Open Laboratory, The University of Tokyo
Invited Speaker: Prof. Isao Tokuda (School of Information Science, Japan Advanced Institute of Science and Technology)

Title: Biomechanical modeling of excised larynx experiments
       - Voice instabilities and register transitions -

Abstract:
Biomechanical modeling is carried out to elucidate excised 
larynx experiment of human vocal folds. The excised larynx 
experiment has been developed since 1957 to study detailed 
oscillatory mechanism of the vocal folds, which are not easy 
to be observed for living human subjects. In the experiment, 
the larynx is blown via a constant rate of air-flow. With a
controlled change of the tension of the vocal folds, the 
experimental system gives rise to a variety of nonlinear 
oscillations including limit cycles, subharmonics, 
biphonation (tori), and chaos. Of special interest are 
coexistence of chest-like and falsetto-like vibrations as 
well as abrupt jumps between the two vibrations accompanying 
hysteresis. 
As a biomechanical model, a simplified 3-mass model is 
constructed by adding a third mass on top of the well known 
2-mass model. Simulation study shows that the simplified 
3-mass model can vibrate in both chest-like and falsetto-like 
modes. Variation of a tension parameter which mimics 
activities of laryngeal muscles can induce transitions 
between the two modes. For reduced rest areas and damping
constants, we find extended coexistence of chest and 
falsetto as observed experimentally. Subharmonics and 
deterministic chaos are observed close to bifurcation points 
of the two oscillations. We discuss that 2-dimensional 
bifurcation diagrams are helpful to understand the rich 
variety of voice instabilities.