Generalization of Interarticulator Timing Control: Evidence From Tongue-Jaw and Lip-Jaw Kinematics Using Electromagnetic Articulography.

Background: In skilled speech production, the motor system coordinates the movements of distinct sets of articulators to form precise and consistent constrictions in the vocal tract at distinct locations, across contextual variations in movement rate and amplitude. Research efforts have sought to uncover the critical control parameters governing interarticulator coordination during constriction formation, with a focus on two parameters: (a) latency of movement onset of one articulator relative to another (temporal parameters) and (b) phase angle of movement onset for one articulator relative to another (spatiotemporal parameters). Consistent interarticulator timing between jaw and tongue tip movements, during the formation of constrictions at the alveolar ridge, was previously found to scale more reliably than phase angles across variation in production rate and syllable stress. In the present study, we test whether these temporal regularities generalize to another set of articulators, namely, the jaw and lower lip, during the formation of constrictions at the lips.

Method: Eight talkers produced vowel-consonant-vowel (VCV) sequences, recorded using electromagnetic articulography, with variation in production rate and syllable stress. V was /ɑ/-/ɛ/ and C was alveolar /t/-/d/ or bilabial /p/-/b/. Two measures were obtained: (a) the timing of tongue tip/lower lip raising onset for intervocalic C, relative to jaw opening-closing cycles for the flanking vowels, and (b) the angle of tongue tip/lower lip raising onset for intervocalic C, relative to the jaw phase plane.

Results: Across both sets of articulators, consonant-related movement onset latencies scaled more consistently with variation in the jaw opening-closing cycle than phase angles. Furthermore, movement onset latencies were more strongly affiliated with utterance type than phase angles.

Conclusion: Findings demonstrate that precise temporal coordination of articulator movements regulates the formation of precise constrictions, independent of the specific set of articulators involved or where in the vocal tract the constriction is produced.