Coarticulation of speech and smile movements

Abstract

Facial expressions and speech movements can impose conflicting demands on articulators. For example, the lip spreading movement associated with smiling is incompatible with bilabial closures for /m/, /b/ or /p/. Anecdotal evidence suggests this conflict may resolve as labiodental stop variants (see http://phonetic-blog.blogspot.ca/2012/03/u.html), though this discussion has been controversial [Ladefoged & Maddieson 1996, p. 18]. The simplest model of coarticulation—one of unmediated superposition of muscle activations [Gick et al., 2013, POMA 060207]—predicts that the outcome of this conflict should be determined by summing opposing forces due to competing muscle activations. If so, varying degrees of smile and varying degrees of closure force (e.g., for different stop consonants) should be expected to produce distinct outputs. Previous work suggests that closures for /m/, /b/ and /p/ vary (increasingly) in both intraoral pressure [Lubker & Parris 1970, JASA 47: 625] and muscle force [Gick et al. 2012, JASA 131: 3345]. An experiment will be presented in which bilabial stops are produced under varying smile conditions. Preliminary results indicate that labiodental stop variants occur more frequently for lower-force stops under higher-force smile conditions, as predicted. Implications for models of coarticulation will be discussed. [Funding from NSERC.]