Interarticulator Speech Coordination: Timing Is of the Essence.

Abstract

In skilled speech production, sets of articulators, such as the jaw, tongue, and lips, work cooperatively to achieve task-specific movement goals, despite rampant contextual variation. Efforts to understand these functional units, termed coordinative structures, have focused on identifying the essential control parameters responsible for allowing articulators to achieve these goals, with some research focusing on temporal parameters (relative timing of movements) and other research focusing on spatiotemporal parameters (phase angle of movement onset for one articulator, relative to another). Here, both types of parameters were investigated and compared in detail. Ten talkers recorded nonsense, disyllabic /tV#Cat/ utterances using electromagnetic articulography, with alternative V (/ɑ/-/ɛ/) and C (/t/-/d/), across variation in rate (fast-slow) and stress (first syllable stressed-unstressed). Two measures were obtained: (a) the timing of tongue-tip raising onset for medial C, relative to jaw opening-closing cycles and (b) the angle of tongue-tip raising onset, relative to the jaw phase plane. Results showed that any manipulation that shortened the jaw opening-closing cycle reduced both the relative timing and phase angle of the tongue-tip movement onset, but relative timing of tongue-tip movement onset scaled more consistently with jaw opening-closing across rate and stress variation. These findings suggest the existence of an intrinsic timing mechanism (or "central clock") that is the primary control parameter for coordinative structures, with online compensation then allowing these structures to achieve their goals spatially. https://doi.org/10.23641/asha.22144259.