Producing whole speech events: differential facial stiffness across the labial stops

Abstract

It has long been assumed that the labial stops (e.g., [p], [b], [m]) are articulatorily identical. However, recent evidence [Abel et al. ISSP, 2011] shows that these labial stops are visually distinct. This distinction could result from differential passive responses to air pressure differences across the stops, or could reflect an active difference in facial muscle activation. An active difference would challenge the simplicity of unidimensional physical target-based speech production models. A pilot study was conducted in which air was blown simultaneously into a speaker's mouth and nose just at the onset of /p/ and /m/ closures. Preliminary results show displacement of the cheeks and lips at /m/ onset, but not at /p/ onset. These results indicate different initial muscular settings for these sounds, presumably to stiffen the face in anticipation of the increased oral air pressure for /p/. Biomechanical simulation using ArtiSynth (www.artisynth.org) confirms that this outcome is consistent with activation of distinct muscle sets across the stops. These findings suggest that speech tasks include aspects of the “whole” event, including aerodynamics, rather than being determined by unimodal spatial targeting.