Producing whole speech events: Anticipatory lip compression in bilabial stops Free

Bilabial stops /b/, /p/, and /m/ ostensibly share a common lip constriction. Recent evidence shows that different bilabial stops involve distinct facial muscle activations, suggesting that oral speech movements anticipate aerodynamic conditions [Gick et al. Proc. Acoust. (2012) 2pSC1]. The present study investigates how the lips themselves behave in whole speech events. Existing models of speech production governing only articulatory motions predict that lip compression would respond to changes in aerodynamic conditions rather than anticipating such changes; a model that includes whole events predicts anticipatory activation of lip muscles with concomitant kinematic lip compression, but only in cases where a real increase in air pressure is expected. Lip kinematics were recorded using OptoTrak to trace lip movements of bilabial stops in response to imperative acoustic stimuli. Results show consistent anticipatory lip compression in spoken /b/ and /p/, but not in non-speech jaw opening movements and only sporadic compression in mouthed /b/ and /p/, where air pressure is not expected to increase. Biomechanical simulation using an orofacial model developed within the Artisynth simulation toolkit (www.artisynth.org) confirms anticipatory muscle activations. These findings support a model of speech tasks wherein coordinated body-level muscular systems govern whole speech events.