Vibration in a self-oscillating vocal fold model with left-right asymmetry in body-layer stiffness

Abstract

This study compares the phonatory behavior of an asymmetric vocal fold model to that of each individual vocal fold model in a hemi-configuration. Although phonation frequencies of the two folds in hemi-configurations had a ratio close to 1:3, a subharmonic synchronization between the two folds was not observed in the asymmetric model. Instead, the vibratory behavior was dominated by the dynamics of one fold only, and the other fold was enslaved to vibrate at the same frequency. Increasing subglottal pressure induced a shift in relative dominance between the two folds, leading to abrupt changes in both vibratory pattern and frequency.

Figure 1

Sketches of the soft-body model (left) and the rigid-body model (right) used in this study.

Figure 2

The amplitude (left column) and power spectra (right column) of the subglottal acoustic pressure as a function of increasing and decreasing subglottal pressure for the soft-body model in a hemi-model configuration (first row), the rigid-body model in a hemi-model configuration (second row), and the asymmetric vocal fold model (last row). In the sound pressure amplitude plots on the left column, ○ denotes data obtained for increasing subglottal pressure; ▼ denotes data obtained for decreasing subglottal pressure.

Figure 3

Spatiotemporal plots of the medial-lateral (left column) and superior-inferior (right column) components of the vocal fold surface displacement for a coronal slice of the soft-body model (top row) and rigid-body model (bottom row) in a hemi-model configuration. The abscissa is time, and the ordinate is the spatial location in the superior-inferior direction, with increasing values in the superior direction. The coronal slice was taken at the midpoint between anterior and posterior extremes.

Figure 4

Time history of a medial-lateral image slice of the asymmetrical vocal folds from a superior view. (a) First vibratory regime, the slice was taken from the middle in the anterior-posterior direction, (b) first vibratory regime, the slice was taken from the anterior quarter in the anterior-posterior direction, (c) second vibratory regime, the slice was taken from the middle in the anterior-posterior direction, and (d) second vibratory regime, the slice was taken from the anterior quarter in the anterior-posterior direction.