Across session temporal stability of the lip–jaw complex in bilabial closure

Abstract

Movements of the tongue, lips, and jaw were transduced by electromagnetic midsagittal articulography. A single session included 20 repetitions of /pap/, /tat/, and /sas/ imbedded in a carrier phrase at normal, slow, and fast speech rates. Seven talkers completed three sessions at 1 week intervals. Reported here are across session comparisons of temporal ordering and relative timing of the movement of the lips and jaw for labial closure at normal rates. The predominant sequence patterns are those in which either upper or lower lip movement occurs first and jaw movement occurs last. Across-subject comparisons show that either lip lead sequence is equally likely to occur. Within-subject across-session comparisons show no clear preference for either lip lead sequence for some subjects, and reversals in dominate lip lead sequences for other subjects. Across-session stability of temporal order is related to interarticulator relative time: Subjects who demonstrate tight coupling of the upper and lower lips have a higher probability of producing both lip-lead sequences, whereas subjects who demonstrate longer interarticulator relative timing produce consistent sequence patterns across sessions. Temporal measures representing the central tendencies of the complete set of session closure gestures are most stable across sessions. [Work supported by NIH DC-00121 to Haskins Laboratories and University of Illinois research grant.]