Grosser, J., Natke, U., Langefeld, S., & Kalveram, K. Th. (2001) Reduction in stuttering by delayed and frequency shifted auditory feedback: Effects of adaptation and sex differences. In H. G. Bosshardt, J. S. Yaruss & H. F. M. Peters (Eds.), Fluency Disorders: Theory, Research, Treatment and Self-help. Proceedings of the Third World Congress of Fluency Disorders in Nyborg, Denmark. Nijmegen: Nijmegen University Press, 422-426.
Eleven women and eleven men who stutter had to read five text passages, each with non altered, delayed (53 msec) and frequency shifted (-1/2 octave) auditory feedback, provided by headphones. Stuttering was measured as Percentage of Discontinuous Speech Time, by which durations of all stuttering moments are determined and related to the entire duration of the speech sample. For both sexes stuttering was reduced by delayed and also by frequency shifted auditory feedback. No substantial increases in stuttering over the time within the conditions with modified feedback were found. Furthermore, the results show that male subjects reacted with reduced speech rate under delayed auditory feedback while women did not. Neither group exhibited a reduction in speech rate under frequency shifted auditory feedback. It is concluded that a reduction of speech rate is not necessarily associated with fluency enhancement by DAF and FAF. Future studies should address adaptation effects to provide more information about underlying mechanisms in fluency enhancement.