Does articulatory setting provide some mechanical advantage for speech motor action?

Abstract

Articulatory setting postures adopted during speech production are examined with the goal of determining whether setting postures are more mechanically advantageous than rest positions in facilitating motion of vocal tract articulators toward task goals. Articulatory simulations using the Task Dynamics Application (TADA) suggest that setting postures afford large changes with respect to speech tasks for relatively small changes in low-level speech articulators, thus affording greater mechanical advantage as compared to absolute rest postures. This study investigates this hypothesis using real-time Magnetic Resonance Imaging (rtMRI) data of read and spontaneous speech elicited from five healthy speakers of American English. Frames corresponding to inter-speech pauses, speech-ready intervals, and absolute rest intervals were identified and image features were automatically extracted to quantify the vocal tract postures in terms of both task-level constriction variables and articulatory variables. Locally Weighted Regression is then used to estimate the ratio of task velocities to articulator velocities (i.e., the lever or speed ratio) at postures corresponding to the different intervals of interest. Results show substantially higher speed ratios at inter-speech and ready postures as compared to absolute rest postures. [Work supported by NIH.]