The effect of manipulating phonation duration on stuttering.

Two single-subject experiments with two adult stutterers were conducted to assess the effect of changing the frequency of phonation intervals that were shorter or greater than prescribed durations during spontaneous speech. Both subjects modified the frequency of prescribed phonation intervals and showed changes in the frequency of these intervals that were positively related to decreases and increases in stuttering frequency. A perceptual analysis of the subjects' speech quality during phonation control conditions showed that when stuttering frequency was reduced, listeners could detect changes in the speech quality of both subjects; however, only one subject's speech during these conditions was described as nonnormal sounding. The therapeutic and theoretical implications of these findings are discussed.