COMPENSATION STRATEGIES FOR THE PERTURBATION OF THE ROUNDED VOWEL [U]USING A LIP TUBE - A STUDY OF THE CONTROL SPACE IN SPEECH PRODUCTION

A labial perturbation of the French rounded vowel [u] was used to exam ine the respective weights of the articulatory and acoustic levels in the control of vowel production. A 20-mm-diam lip tube was inserted be tween the lips of the speakers. Acoustic and x-ray articulatory data w ere obtained for isolated vowel productions by 11 native French speake rs in normal and lip-tube conditions. Compensation abilities were eval uated through accuracy of the F1-F2. pattern. Possible compensations w ere examined from nomograms using the new model of Fant [ISCLP 92 Proc eedings (University of Alberta, Edmonton, 1992)]. Acoustic interpretat ions of the articulatory changes were made by generating area function s from midsagittal views, used together with a harmonic acoustic model . For the first perturbed trial, immediately after the insertion of th e tube, no speaker was able to produce a complete compensation, but cl ear differences between speakers were observed: Seven of them moved th e tongue and hence limited the deterioration of the F1-F2 pattern, whe reas the remaining four did not show any pertinent articulatory change . These data support the idea of speaker-specific internal representat ions of the articulatory-to-acoustic relationships. The results for th e following 19 perturbed trials indicate that speakers used the acoust ic signal in order to elaborate an optimal compensation strategy. One speaker achieved complete compensation by changing his constriction lo cation from a velo-palatal to a velo-pharyngeal region of the vocal tr act. Six others moved their tongues in the right direction, achieving partial acoustic compensation, while the remaining four did not compen sate. The control of speech production thus seems to be directed towar d achieving an auditory goal, but completely achieving the goal may be impossible because of speaker-dependent articulatory constraints. It is suggested that these constraints are due more to speaker-specific i nternal representation of articulatory-to-acoustic relationships rathe r than to anatomical or neurophysiological limitations. Speech control could thus be ensured partly with the use of this internal representa tion, and partly - particularly under perturbed conditions - by monito ring the acoustic signal. (C) 1995 Acoustical Society of America.