Temporal coordination of articulatory movements across speech segments: Fixed onsets with flexible kinematic trajectories

Articulatory Phonology and Task Dynamics posit that phonological structure emerges from sequences of vocal tract constrictions, produced through precisely coordinated and goal-directed movements of otherwise independently controlled articulators, such as the tongue and jaw. However, these theories do not clearly specify which aspects of articulatory motion are reliably coordinated across signal stretches spanning multiple segments. The present study tested the hypothesis that phonological structure is realized through temporal coordination of movement onsets across successive segments. Using electromagnetic articulography, we recorded tongue-tip and jaw movements as participants produced vowel-consonant-vowel sequences with varied vowels (/ɑ/-/ɛ/) and alveolar stops (/t/-/d/) across rate (fast vs normal) and stress (first-syllable stressed vs unstressed) conditions. Temporal coordination between vowel-related jaw and consonant-related tongue-tip movements was analyzed across conditions. Results showed that movement onset timing across articulators was consistently maintained, such that inter-movement intervals scaled reliably across conditions, whereas the timing of peak displacements and offsets varied with rate and stress. Importantly, movement onsets scaled more reliably in absolute time than when computed proportionally to movement duration. Collectively, these findings demonstrate that articulatory movement onsets are governed by fixed timing control, whereas later portions of movement trajectories are flexibly adjusted to meet evolving task demands.