Vertical motion during modal and pressed phonation: magnitude and symmetry

Vertical motion of the vocal folds during phonation is a possible diagnostically significant feature. However, it is difficult to judge vertical motion through the typical two-dimensional stroboscopic display. Through high-speed videoendo-scopy (HSV), the dynamics of vocal fold vibration are easier to appreciate; however, the traditional HSV is also two-dimensional. Recently, a method to display a three-dimensional (3D) image of vocal fold vibration was published. This method, as well as stroboscopy and HSV, was utilized to study vertical motion magnitude and symmetry during modal and pressed phonations in normophonic speakers. Vertical motion judgments were rated as at least 16% more possible from the HSV-derived playbacks than from stroboscopy. The assessments from the 3D playback were different than those from the two-dimensional HSV playback for magnitude, however a similar trend was realized. The findings demonstrate consistently greater magnitudes of vertical motion during pressed phonations. Asymmetry of vertical motion was appreciated in both modal and pressed phonations. The results of this study concur with the concept of increased vertical motion during pressed phonation and recommend further investigations of the typicality of this important feature of vocal fold vibration in various modes and registers of normal and pathologically influenced phonation. I. INTRODUCTION Visualizing vocal fold vibratory behavior is widely accepted as an integral part of a complete voice evaluation. This vibratory behavior is known to move in three dimensions: laterally, longitudinally, and vertically. The lateral movement of vocal fold vibration is the most widely discussed and utilized in clinical voice evaluations as an indication of vocal fold stiffness. The longitudinal motion of vocal fold vibration has begun to be investigated and used as part of the clinical visualization protocol. However, the normal limits of variation in longitudinal motion remain unclear. The third dimension of vocal fold vibration, vertical motion is not a common feature rated during the stroboscopic evaluation. While furthering our knowledge of lateral and longitudinal vocal fold vibratory deviations and their prevalence in various disorders is an important task, this paper narrows its scope to investigating the vertical motion of vocal fold vibration.