Inter-articulator coordination in speech production: Timing is of the essence

In skilled speech production, sets of vocal-tract articulators work cooperatively to achieve task-specific goals, in spite of contextual variation. Efforts to understand these functional units have focused on identifying control variables responsible for allowing articulators to achieve these goals, with some research focusing on temporal variables (relative timing of movements) and other research focusing on spatiotemporal variables (phase angle of movement onset for one articulator, relative to another). Here, both types of variables were examined. Ten talkers recorded /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: (1) timing of tongue-tip raising onset for medial C, relative to jaw opening-closing; (2) 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. This finding supports the hypothesis that an intrinsic timing mechanism is the control variable for interarticulatory relations, with immediate compensation then allowing these structures to achieve their goals spatially.