Articulatory control of vowel length for contiguous jaw cycles: the effects of speaking rate and phonetic context.

The current study examined contiguous cycles of jaw movement in order to determine if select suprasegmental manipulations operate globally across the entire utterance, while phonetic changes are more locally administered. Specifically, articulatory kinematics were examined to determine if intra- and inter-articulatory spatial and temporal organization across manipulations of speaking rate was maintained for both jaw cycles while differing between the two cycles for phonetic changes (i.e., in coda composition) specific to the second jaw cycle. Five normal speakers repeated the syllables /paep/, /paeps/, and /paepst/, embedded in the carrier phrase, "Now say again," using slow, normal, and fast speaking rates. Measures were made of the magnitude of jaw opening peak velocity and time to peak velocity, as well as of coarticulatory overlap and interarticulator timing, for the first jaw cycle (jaw lowering for /eI/ in "say" to the first /p/) and the second jaw cycle (jaw lowering for /ae/ to the second /p/). The current data indicate that, for intra-articulatory kinematics, the manipulation of phonetic context resulted in localized adjustments, whereas the manipulation of speaking rate was applied globally across the utterance. Conversely, for inter-articulatory kinematics, the upper lip-jaw synergy was reconfigured across the utterance for manipulations of speaking rate, whereas this synergy was maintained for localized manipulations in phonetic context. Results are discussed with respect to motor strategies being flexibly implemented as a result of contextual variation and speech rate.