TONGUE SURFACE DISPLACEMENT DURING BILABIAL STOPS

The goals of this study were to characterize tongue surface displaceme nt during production of bilabial stops and to refine current estimates of vocal-tract wall impedance using direct measurements of displaceme nt in the vocal tract during closure. In addition, evidence was obtain ed to test the competing claims of passive and active enlargement of t he vocal tract during voicing, Tongue displacement was measured and to ngue compliance was estimated in four subjects during production of /a ba/ and /apa/. All subjects showed more tongue displacement during /ab a/ than during /apa/, even though peak intraoral pressure is lower for /aba/, In consequence, compliance estimates were much higher for /aba /, ranging from 5.1 to 8.5 X 10(-5) dm(3)/dyn. Compliance values for / apa/ ranged from 0.8 to 2.3 X 10(-5) cm(3)/dyn for the tongue body, an d 0.52 X 10(-5) for the single tongue tip point that was measured. Fro m combined analyses of tongue displacement and intraoral pressure wave forms for one subject, it was concluded that smaller tongue displaceme nts for /p/ than for /b/ may be due to active stiffening of the tongue during /p/, or to intentional relaxation of tongue muscles during /b/ (in conjunction with active tongue displacement during /b/). (C) 1997 Acoustical Society of America.