Lip-jaw and tongue-jaw coordination during rate-controlled syllable repetitions

The present study investigated the relationship between functionally releva nt compound gestures and single-articulator component movements of the jaw and the constrictors lower lip and tongue tip during rate-controlled syllab le repetitions. In nine healthy speakers, the effects of speaking rate (3 v s 5 Hz), place of articulation, and vowel type during stop consonant-vowel repetitions (/pa/, /pi/, /ta/, /ti/) on the amplitude and peak velocity of differential jaw and constrictor opening-closing movements were measured by means of electromagnetic articulography. Rather than homogeneously scaled compound gestures, the results suggest distinct control mechanisms for the jaw and the constrictors. In particular, jaw amplitude was closely linked t o vowel height during bilabial articulation, whereas the lower lip componen t amplitude turned out to be predominantly rate sensitive. However, the obs erved variability across subjects and conditions does not support the assum ption that single-articulator gestures directly correspond to basic phonolo gical units. The nonhomogeneous effects of speech rate on articulatory subs ystem parameters indicate that single structures are differentially rate se nsitive. On average, an increase in speech rate resulted in a more or less proportional increase of the steepness of peak velocity/amplitude scaling f or jaw movements, whereas the constrictors were less rate sensitive in this respect. Negative covariation across repetitions between jaw and constrict or amplitudes has been considered an indicator of motel equivalence. Althou gh significant in some cases, such a relationship was not consistently obse rved across subjects. Considering systematic sources of variability such as vowel height, speech rate, and subjects, jaw-constrictor amplitude correla tions showed a nonhomogeneous pattern strongly depending on place of articu lation. (C) 2000 Acoustical Society of Amer icn. [S0001-4966(00)05204-8].