A MODEL OF ARTICULATOR TRAJECTORY FORMATION BASED ON THE MOTOR-TASKS OF VOCAL-TRACT SHAPES

This paper presents a modeling study of articulator movements for cont inuous speech utterances. The model determines the trajectories of the articulator movements that form the vocal tract into phoneme-specific shapes. Vowels, for example, are generated based on the specification s of the tract shape (motor tasks) related to the shape of the tongue and lips. Consonants, such as /p/ and /k/, on the other hand, can be g enerated by specifying a closure in the tract between the lips, or bet ween the tongue and the palate. In the model, state variables represen t the active movements of each articulatory organ as the displacement relative to the neutral position. In addition, tract variables are def ined to specify the motor tasks of the lips and tongue as functions of the state variables of the jaw, lips, and tongue: The definition of t he tract variables incorporates the representation of the coordinative structure of the articulatory system between the jaw and the lower li p and between the jaw and the tongue. This coordinative structure allo ws for an infinite number of trajectories that satisfy all of the give n motor tasks. This redundancy is overcome by minimizing the cost func tion so that the movements of each articulatory organ are uniquely det ermined. Articulator movements were simulated for several utterances, and the simulated movements of the jaw, lips, and tongue agree well wi th measured data. The results show that it is valid to use the feature s of vocal-tract shapes to represent motor tasks when modeling articul ator movements acid that the model accurately represents the coordinat ed movements of the articulatory organs. (C) 1995 Acoustical Society o f America.