Effect of speaking rate on labial consonant-vowel articulation

The purpose of this experiment was to study the effect of speaking rate on the articulation of the consonants /p, w/, in combination with the vowels /i, a, u/. Two subjects read a list of nonsense syllables containing /p, w/, in all possible VCV combinations with /i, a, u/, at both moderate and fast speaking rates. EMG recordings from muscles that control movements of the lips, tongue and jaw were recorded simultaneously with high speed lateral view X-ray films of the tongue and jaw, and high speed full-face motion pictures of the lips. For labial consonant production, an increase in speaking rate is accompanied by an increase in the activity level of the muscle (orbicularis oris) and slightly faster rates of lip movement (both closing and opening). Vowel production, however, shows opposite effects: an increase in speaking rate is accompanied by a decrease in the activity level of the genioglossus muscle and, as shown by the X-ray films, evidence of target undershoot. Jaw movement data show more variable, context-dependent effects on speaking rate. Observed differences are explained in terms of the muscle systems involved.