ABSTRACT
A central issue in speech has involved uncovering aspects of articulation that remain invariant in the face of suprasegmental transformations. Much previous experimental work has shown that such invariance is unlikely to be exhibited at the level of individual muscles or articulator movements. Here we introduce the concept of stability of a collective macroscopic variable— the relative phasing of articulatory events—that has been observed to change little across rather large variations in individual articulators' kinematics. To establish the veracity of this concept, we study how articulatory patterns change, with the aim of understanding both stability and change of coordinated speech patterns as two manifestations of the same underlying dynamics. To this end, subjects were asked to say /ip/ or /pi/ repetitively, at increasing speaking rates, while their glottal and lip movements were monitored. In general, the observed interarticulator phase relationships did not depend on the rate-scaling parameter. However, at critical values of rate the relative phase of articulator movements changed markedly. Experiment 2 found that these transition points correspond precisely to perceptual changes in syllable affiliation of the consonant. More generally, the work is directed at reorienting speech research to the identification and analysis of articulatory and perceptual stability instead of its present search for invariants.
