An articulatory analysis of formant asymmetries in symmetric CVC sequences

Abstract

Symmetric CVC sequences (e.g., dVd, bVb, etc.) do not have symmetric formant trajectories. This paper reports a study of this phenomenon using articulatory data and vocal tract modeling. The x-ray microbeam system at the University of Wisconsin tracked the locations of seven gold pellets affixed to the tongue, lips, and mandible of five midwestern English speakers. The speakers read sentences containing symmetric sequences composed of the consonants /d/, /b/, and /s/ and ten vowels in English. Five events in the trajectores most closely associated with the consonant gesture (tongue tip for /d/ and /s/, and lower lip for /b/) were identified: initial and final consonant closure, maximum vowel displacement and maximum velocity during the opening and closing consonant gestures. The data suggest that symmetric CVC sequences are temporally symmetric, with the maximum vowel displacement occurring about half-way between the two consonant closures. Tense and lax vowels differ in the locations of maximum closing and opening velocity (which were also temporally symmetric), with maximum velocities occurring nearer the consonant closures in tense vowels. While the time course of the gestures was symmetric, the locations of the articulators was not. Consonant release and closure generally involved vertical displacement of the tongue before horizontal displacement, giving rise to a circular pattern of movement. There was evidence for this circular pattern of tongue movement for both alveolar and labial consonants. Preliminary vocal tract modeling using the microbeam data to specify the parameters of a vocal tract analog synthesizer has indicated that the pattern of results described above (temporal symmetry, spatial asymmetry) results in formant asymmetries similar to those shown in previous research.