maximal jaw and lip openings

"The results regarding accent show that accented vowels are strongly articulated, having larger maximal jaw and lip openings, extreme maximal tongue positions (lower for /a/ and fronter for lif), greater V-to-V coarticulatory resistance, and larger, longer, and faster movement. As for boundary effects, the results show that vowels at higher prosodic boundaries are strongly articulated, evident in larger maximal lip opening but not in maximal jaw opening, extreme maximal tongue position (lower for both /a/ and /i/), greater V-to-V coarticulatory resistance, and longer, sometimes larger, but not necessarily faster movement. Although accent and boundary both give rise to articulatory strengthening, these effects are not the same. They differ in the dimension in which the tongue is expanded, the involvement of the lips and the jaw, and the movement velocity."

http://www.linguistics.ucla.edu/faciliti/research/choabs.htm