Interarticulator Timing Relations Underlie the Production of Precise and Consistent Vocal Tract Constrictions During Speech

PURPOSE: During speech production, complex patterns of coordinated movements between sets of articulators (e.g., jaw and tongue, jaw and lips) form precise and consistent constrictions at distinct locations along the vocal tract, despite rampant contextual variation. Speech motor control research seeks to uncover basic principles of organization governing interarticulator coordination during constriction formation, assuming many degrees of freedom for controlling articulator movements. This study tested the hypothesis that the motor system reduces degrees of freedom and facilitates coordination by reliably controlling interarticulator timing. METHOD: Ten 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/. Timing relations between peak velocities of condition-specific sets of articulators were determined during oral closure and release for C: jaw, upper lip, and lower lip for bilabial constrictions and jaw and tongue tip for alveolar constrictions. RESULTS: During oral closing, the timing of articulator peak velocities was tightly coupled across scalar changes in rate and stress, such that timing variation in one articulator was accompanied by proportional changes in the timing of another articulator. In contrast, the timing of peak velocities was less tightly coupled during subsequent oral opening. The timing of peak velocities was also more reliably differentiated by rate/stress condition during oral closing than opening, indicating that speech articulator movements are temporally coordinated primarily based on the part of movement related to constriction formation, rather than its subsequent release. CONCLUSION: Findings align with the view that stable interarticulator timing relations underlie the achievement of precise and consistent vocal tract constrictions during speech. SUPPLEMENTAL MATERIAL: https://doi.org/10.23641/asha.28791872.