  Purpose: The authors' general aim is to use biomechanical models of speech
articulators to explore how possible variations in anatomical structure
contribute to differences in articulatory strategies and phone systems across
human populations. Specifically, they investigated 2 issues: (a) the link
between lip muscle anatomy and variability in lip gestures and (b) the
constraints of coupled lip/jaw biomechanics on jaw posture in labial sounds.
Method: The authors used a model coupling the jaw, tongue, and face. First, the
influence of the orbicularis oris (OO) anatomical implementation was analyzed
by assessing how changes in depth (from epidermis to the skull) and
peripheralness (proximity to the lip horn center) affected lip shaping. Second,
the capability of the lip/jaw system to generate protrusion and rounding, or
labial closure, was evaluated for different jaw heights. Results: Results
showed that a peripheral and moderately deep OO implementation is most
appropriate for protrusion and rounding; a superficial implementation
facilitates closure; protrusion and rounding require a high jaw position; and
closure is achievable for various jaw heights. Conclusions: Models provide
objective information regarding possible links between anatomical and speech
production variability across humans. Comparisons with experimental data will
illustrate how motor control and cultural factors cope with these constraints.
