COORDINATION AMONG ARTICULATORS IN SPEECH

The present experiments explore temporal relationships among articulatory events as a function of changes in speaking rate and syllable stress. The first experiment was designed to examine the adequacy of two basic types of explanation that have been proposed for these changes. One view is that the segmental commands for syllables spoken quickly and for unstressed syllables show more extensive temporal overlap than the same syllables spoken more slowly or with greater syllabic stress. An alternative view is that the temporal relationships among articulations remain constant over changes in speaking rate and stress but the individual gestures themselves vary. The results support the latter hypothesis. Electromyographic (EMG) activity in the articulatory muscles examined (genioglossus and orbicularis oris) showed that aspects of the motor activity underlying lip movements for bilabial stops and tongue fronting for the vowels /i/ and /e/ maintained a tight absolute temporal constancy. The second experiment explored whether this constancy of absolute temporal patterns over changes in speaking rate and syllable stress is unique to the genioglossus and orbicularis oris muscles, is a general characteristic of speech motor control, or is a special case of a more general constraint on relative temporal patterns. EMG recordings from lip, tongue and jaw muscles were obtained so that temporal aspects of muscle activity could be examined over more phonetic segments than possible in Experiment 1. The results suggest that an adequate description of speech motor coordination may be in terms of relative timing constraints. The similarity between this view of coordination among articulators in speech and the style of coordination in other motor systems is also discussed.