Yadong Liu defends his PhD

In this dissertation, I investigated the control of postures in the human vocal tract and integrated these controls into speech models using simulative methods and provided correspondent behavioral evidence. Chapter 1 presents the theoretical background, highlighting that although speech postures behave similarly to other postures, they have only been observed among English speakers and have not been incorporated into any speech motor control models. This chapter then proposes a parallel control model that includes both speech postural control and movement control. The simulated outcomes support the view that speech posture, like body posture, constitutes a necessary and universal substrate for speech (tested in Chapter 2) which is maintained under perturbation (tested in Chapter 3), and that anticipatory postural adjustments should contribute to equilibrium in the context of internal perturbations (tested in Chapter 4). Chapter 2 examines the universality of the lingual bracing posture, observing that it is present across different languages. Chapter 3 investigates the robustness of the lingual posture under external perturbations, finding that the lingual bracing posture is consistently maintained with the presence of external perturbation. Chapter 4 studies the interaction of the smiling posture with internal perturbations, revealing that the posture is also robustly maintained with some anticipatory adjustments. Finally, Chapter 5 reviews the dissertation and summarizes the major findings.