Vocal effort and intelligibility: a preliminary study with aerodynamic measurements during production of consonants
Résumé
Production of voice during vocal effort has been studied mainly in terms of the subglottic pressure and derivatives formulas during the production of vowels. The study of the production of consonants seems essential to integrate vocal effort in the general framework of hyperarticulation proposed by Lindblom (1990): the use of a "loud" or "clear" voice is accompanied by an increase in various indices of speech intelligibility, especially the contrast between voiced and unvoiced consonants which is the subject of this work. However, indirect methods, being inapplicable here, we conducted a pilot study using the principle of transtracheal direct measurement of subglottic pressure on the lead author of the study. We studied on the same speaker during the same session, 6 successive productions of a series of non-words including the contrast f / v in 12 different vowel contexts and 4 categories of speech (threshold, modal, clear, loud). The productions were performed randomly. Our goal was to show that in loud voice and in clear voice there was an enhancement of the voicing contrast manifested by the increase of the difference of transglottal gradient (TGP) between voiced and unvoiced consonants. SGP, OAF, IOP, Fo, Int, spectrum has been recorded simultaneously using the EVA® device (SQ-Lab, France). Our results are fully consistent with our hypothesis. For sample, on non-word /avafa/ , difference between /f/ and /v/ in TGP is 1.2 hPa at threshold, 2.5 hPa in modal voice, 4 hPa in clear voice and 9 hPa in loud voice. Other results are consistent as well. These results demonstrate that the use of a "clear" voice (that aims to improve intelligibility in certain circumstances) is based on a more energetic process than the modal voice comparable to the loud voice. They confirm that vocal effort must be integrated into a unified approach of speech production and cannot be considered independently. These preliminary results should be confirmed by studies on various normal and pathological subjects.