How do ventricular folds behave during vocal effort ?
Résumé
The human two ventricular folds constitute an additional laryngeal vibrator, whose biomechanical properties differ from those of the vocal folds. Often considered solely anecdoticaly, they may adduct, get into contact, and even vibrate during speech and singing. This present study aims at characterizing their behavior during situations of vocal effort, such as shouted speech, growls, and crescendos-decrescendos. A database of phonatory gestures which accompanies vocal effort has been constituted by the cinematographic, audio and electroglottographic recordings of five speakers and three singers. The signals have been recorded simultaneously and synchronized to the high-speed laryngeal images. A ventricular-fold systematic movement is observed during vocal effort, as compared to usual phonation. The two folds get closer, and this movement may go with a spectral increase of energy in the 2-4 kHz frequency band with no direct correlation on vocal intensity. The closing movement is either localized on the median and/or antero-median part, or it may occur over the whole fold length. In the case of contact, the ventricular folds may start to vibrate, periodically or not, and in phase or not with the vocal-folds vibratory movement. Using an aerodynamical theoretical approach, the influence of a supra-laryngeal constriction on the glottal vibratory movement has been evidenced (Bailly et al., 2008). This aerodynamical modeling approach is combined here with high-speed visualization in order to predict the physical impact of the observed ventricular constrictions on glottal vibration, similarly to a previous study on period-doubling phonation (Bailly et al., 2010). Ventricular area is detected on high-speed laryngeal images, and given as an input parameter to the model. Glottal vibratory behavior is then simulated by applying a two-mass model inspired from Ruty et al. (2007). The resulting signal is compared with glottal contact area as measured by electroglottography. Bailly, L., Pelorson, X., Henrich, N., and Ruty, N. (2008). "Influence of a constriction in the near field of the vocal folds: Physical modeling and experimental validation," J. Acoust. Soc. Am. 124(5), 3296-3308. Bailly, L. (2009). "Vocal fold and ventricular fold vibration in period-doubling phonation: Physiological description and aerodynamic modeling," J. Acoust. Soc. Am. 127(5), 3212-3222. Ruty, N., Pelorson, X., Van Hirtum, A., Lopez-Arteaga, I., and Hirschberg, A. (2007). "An "in-vitro‟ setup to test the relevance and the accuracy of low-order vocal folds models," J. Acoust. Soc. Am. 121 (1), 479-490.