Spectrographic study of vowels in stutterers' fluent speech.

Measurements were made of the formant frequencies and formant transitions associated with the vowels /i/, /ae/ and /u/ produced by seven moderate-to-severe stutterers when they read fluently in a control (normal) condition and under four experimental condition: masking noise, delayed auditory feedback, rhythmic pacing, and whispering. The first and second formant frequencies in an isolated /hVd/ context were more centralized than those reported for nonstutterers. The formant frequencies were centralized even more in reading, but varied little across conditions despite changes in fluency, speaking rates, and vowel duration. Duration and rate of formant transitions also were essentially the same across conditions. These findings and those reported in other studies indicate that stutterers' vowel production is more restricted, spatially and temporally, than nonstutterers'.