Acoustic and articulatory features of diphthong production: a speech clarity study.

PURPOSE The purpose of this study was to evaluate how speaking clearly influences selected acoustic and orofacial kinematic measures associated with diphthong production. METHOD Forty-nine speakers, drawn from the University of Wisconsin X-Ray Microbeam Speech Production Database (J. R. Westbury, 1994), served as participants. Samples of clear and conversational productions of the word combine were extracted for analysis. Analyses included listener ratings of speech clarity and a number of acoustic and articulatory kinematic measures associated with production of the diphthong /aI/. RESULTS Key results indicate that speaking clearly is associated with (a) increased duration of diphthong-related acoustic and kinematic events, (b) larger F1 and F2 excursions and associated tongue and mandible movements, and (c) minimal evidence of change in formant transition rate. CONCLUSIONS Overall, the results suggest that clarity-related changes in diphthong production are accomplished through larger, longer, but not necessarily faster diphthong-related transitions. The clarity-related adjustments in diphthong production observed in this study conform to a simple model that assumes speech clarity arises out of reduced overlap of articulatory gestures.