Acoustic estimates of vowel centralization in persons who stutter

The magnitude of tongue movement for fluently produced utterances of persons who stutter and those of normally fluent controls was inferred through examination of the vocal tract vowel space. Fifteen adult males served as subjects comprising separate groups of untreated stutterers, stutterers who had completed a fluency-shaping treatment program, and nonstuttering controls. The steady-state portion of formant one (F1) and formant two (F2) was examined in the production of various CVC tokens embedded in a carrier phrase. Average F1 and F2 values for |i|, |a|, and |u| were plotted in an F1−F2 vowel space triangle for each subject. The corresponding vowel space was measured by determining the area (Hz2) of the triangle. Results indicated the untreated group of persons who stutter had the smallest average vowel space, while the largest vowel space was observed in the control group. Discussion focuses on the vocal tract articulation characterizing fluent speech production.