A NOTE ON VOWEL CENTRALIZATION IN STUTTERING AND NONSTUTTERING INDIVIDUALS

Inferences were made regarding vocal tract vowel space during fluently produced utterances through examination of the first two formant freq uencies, Fifteen adult males served as subjects, representing separate groups of untreated and treated individuals who stutter and nonstutte ring controls. The steady-state portion of formant one (F1) and forman t two (F2) was examined in the production of various CVC tokens contai ning the vowels /i/, /u/, and /a/. Vocal tract vowel space was estimat ed three ways. The first analysis scheme involved measurement of forma nt frequency spacing. The second measure involved calculating the area of the vowel space triangle. The third measure was based on calculati ng the average Euclidean distance from each subiect's midpoint ''centr oid'' vocal tract position to the corresponding /i/, /u/, and /a/ poin ts on the vowel triangle. The formant frequency spacing measures prove d to be most revealing of group differences, with the untreated stutte rers showing significantly greater vowel centralization than the treat ed group and control group. Discussion focuses on the vocal tract arti culation characterizing fluent speech productions and possible treatme nt implications for persons who stutter.