Precision of Tongue Control for Task-Relevant Articulatory Goals Diminishes Without Real-Time Auditory Feedback

A fundamental issue in speech motor control is the extent to which the nervous system uses real-time auditory feedback to regulate the control of articulatory movements, which function to produce acoustic speech signals by forming constrictions in the vocal tract. This study explored the hypothesis that real-time auditory feedback about one's own articulatory movements is continuously integrated throughout motor execution to support the precise regulation of task-relevant movement goals-those most critical for achieving target constrictions-especially for articulators with more degrees of freedom in their actions.

We examined the control of tongue-tip and jaw movements during the production of intervocalic stop consonantal constrictions when real-time auditory feedback was masked with babble noise. Seven subjects with normal hearing produced vowel-consonant-vowel sequences, recorded using electromagnetic articulography, with variation in production rate (fast-normal) and syllable stress (first syllable stressed-unstressed). The vowel was inherently long /ɑ/ or inherently short /ɛ/, and the consonant was voiceless /t/ or voiced /d/. Subjects produced the target utterances during two feedback conditions: unmasked and noise masked. In each feedback condition, tongue-tip and jaw movements were characterized by assessing peak velocity and the timing of peak velocity during both the formation and release of the target consonantal constrictions.

All subjects showed reduced precision (increased kinematic variability) in tongue-tip control, but not jaw control, during constriction formation in the noise-masked feedback condition. Precision during the subsequent constriction release remained unaffected for both articulators regardless of feedback condition.

Findings are compatible with the view that real-time auditory feedback helps regulate the precision of articulatory control during task-relevant aspects of movement (i.e., constriction formation) and that articulators with greater flexibility-such as the tongue-require heightened sensory feedback to support fine-grained motor control.