The articulatory trajectories of the tongue in the muscle force space

Abstract

The motor command generation mechanism for speech production may be considered as a transformation from a planned articulatory trajectory to multiple motor commands. This study aims to reconstruct a representation of such a trajectory by analyzing EMG signals associated with tongue movements in speech. Tongue EMG data recorded during /schwapVp/ utterances [Baer etal., Ann. Bull. RILP 22, 7–20] were analyzed on the basis of antagonistic relationships among four extrinsic tongue muscles: the genioglossus anterior (GGA), posterior (GGP), the hyoglossus (HG), and the styloglossus (SG). The computed patterns of equilibrium forces derived from EMG were then mapped into the muscle force space, defined by a coordinate system with GGP–HG and GGA–SG axes. The articulatory trajectories obtained correspond well to assumed tongue movements for the utterances. The vowel distribution in the muscle force space shows analogous patterning to vowel distributions in the acoustic and perceptual domains. This coincidence between the articulatory and perceptual representations of vowels implies the co-evolution of the somatoneural relation, and shows evidence of the modular organization of human speech production and perception. [Work supported in part by an NIH Grant No. 00120 to Haskins Laboratories.]