Individual differences in vowel production.

It is often assumed that a relatively small set of articulatory features are universally used in language sound systems. This paper presents a study which tests this assumption. The data are x-ray microbeam pellet trajectories during the production of the vowels of American English by five speakers. Speakers were consistent with themselves from one production of a word to the next, but the articulatory patterns manifested by this homogeneous group were speaker specific. Striking individual differences were found in speaking rate, the production of the tense/lax distinction of English, and in global patterns of articulation. In terms of a task-dynamic model of speech production, these differences suggested that the speakers used different gestural target and stiffness values, and employed different patterns of interarticulator coordination to produce the vowels of American English. The data thus suggest that, at some level of speech motor control, speech production tasks are specified in terms of acoustic output rather than spatiotemporal targets or gestures.