Kinematic model of the medial surfaces of the vocal folds. The Post-Ant. dimension is the vocal fold length, the Inf.-Sup. dimension is the vocal fold thickness, and the Lateral-Medial dimension is vocal fold displacement. ξ02 and ξ01 are the prephonatory adductory settings of the upper and lower portions, respectively, of the posterior portion of the vocal folds. ξb is the surface bulging, and zn is a nodal point around which the rotational mode of vibration pivots.