Experimental investigation of the effects of frequency-altered auditory feedback on the speech of adults who stutter

A series of single-subject experiments evaluated the effects of frequency-altered auditory feedback (FAF) on the speech performance of four adult males who stutter. Using alterations of plus or minus one octave, FAF was compared with normal auditory feedback (NAF) in oral reading and spontaneous speech with measurements made of stuttered intervals, stutter-free speech rate, and speech naturalness. The effects of extended FAF conditions on spontaneous speech were also evaluated for two subjects who demonstrated a positive response to FAF. Results showed no consistencies across subjects in responses to FAF: One subject showed no response, another produced an initial temporary response, a third showed a deterioration in speech quality with minimal reductions in stuttering, and a fourth displayed substantial and sustained improvements in speech performance. Some implications of these findings for current research and theory about the relationship between stuttering and FAF are discussed.