Articulatory settings facilitate mechanically advantageous motor control of vocal tract articulators

It was recently shown that vocal tract postures assumed during pauses in read speech are significantly different from those assumed at absolute rest. This paper examines whether the former category of “articulatory settings” are more mechanically advantageous than absolute rest postures with respect to speech articulation. Appropriate task and articulator variables are extracted from real-time Magnetic Resonance Imaging (rtMRI) data of five speakers reading aloud. Locally-weighted regression is then used to calculate Jacobian matrices representing the transformation between articulatory task velocities and postural velocities. A measure of mechanical advantage is proposed based on the obtained Jacobian. Speech-ready postures and postures during inter-speech pauses are observed to be significantly more mechanically advantageous as compared to rest postures. Furthermore, other postures, such as those that occur during the production of different vowels and consonants, are shown to have mechanical advantages that lie in between this continuum. These results could provide insights into understanding postural motor control and other linguistic phenomena, such as sonority hierarchies, in speech production. Index Terms: speech production, real-time MRI, articulatory setting, postural motor control, task dynamics, forward kinematics, vocal tract shaping.