Effects of speech rate on vowels produced by stutterers in fluent speech
Résumé
The purpose of this investigation is to analyze the formant structure of vowels produced by stutterers and treated stutterers, by comparing their data with those of control subjects. Moreover, we will study the effects of speech rate increase on the formant structures of the vowels, and that of the three groups of speakers. We chose to analyze French oral vowels [i, a, u], from spectrographic data, in two speech rate conditions: normal and fast. The three segments were placed in sentences which were repeated ten times by stutterers, treated stutterers and control subjects. Concerning control subjects, several studies have shown that an increase of speech rate could provoke a compression of durations and a reduction of the vowel space, i.e. a certain centralization of vowels in this space. What would the result be for stutterers or former stutterers, knowing that the majority of studies have shown a centralization of the vowel space in normal speech rate condition for stutterers? The present investigation is of double interest: a) it provides additional data concerning a possible reduction of the vowel space of stutterers in normal speech rate; b) it tries to verify whether an "undershoot" phenomenon in fast speech rate would appear or not. Our hypotheses are: a) a more restricted vocalic space should be noticed in stutterers‟ fluent speech; b) consequently, no further vowel centralization should be observed when stutterers speak faster. Results show that the formant structure of vowels [i, a, u] is comparable for treated stutterers and for control subjects, whereas it is different for stutterers. F2 is especially responsible for this configuration: it suggests fronting of the tongue. Furthermore, an "undershoot" phenomenon has been observed for controls and treated stutterers in a fast speaking condition. This centralization is not noticed in non-treated stutterers‟ speech, since area of the vowel is similar in the two rate conditions.