The effects of antagonistic gestures on temporal and amplitude parameters of anticipatory labial coarticulation.

Anticipatory lip rounding before neutral versus antagonistic vowel environments was studied in a test of the compatibility notion of a look-ahead scanning mechanism (Henke, 1967). Electromyograms were obtained from orbicularis oris superior, an agonist for lip rounding, and risorius, an agonist for lip spreading, from three normal speakers repeating the nonsense disyllables /tiku/, /taku/, /tuki/, /kikstu/, and /kakstu/ twenty times each. When the syllable-initial vowel was the lip spread vowel /i/, oris activity began earlier and with greater force than for syllable-initial /a/ contexts across all speakers. This finding argues for a revision of a key assumption underlying the look-ahead scan model for anticipatory lip rounding. The encoding program for speech exhibits temporal and amplitude adjustments in its coarticulatory behavior to accommodate in an active way contradictory neuromuscular and biomechanical conditions. These results are discussed with reference to current models of speech production.