Acoustic properties of masking/delayed feedback in the fluency of stutterers and controls

This study examined specific acoustic variables such as auditory masking in the effect of delayed auditory feedback (DAF) on stuttered speech. Eleven stutterers and eleven controls read prose aloud under conditions of modified and masked feedback. The readers' speech was compared under conditions of synchronized and 100-msec delayed speech feedback and under four conditions of synchronized or 100-msec delayed feedback of a low frequency masker or a voice-like masker modulated by the amplitude envelope derived from the speech. Two conditions with continuous envelope masker not thus modulated were also employed. Numbers of syllables read and error frequency were scored. Control subjects were disrupted only by delayed speech feedback, but stutterers' speech was partially ameliorated by all the experimental presentations. In this respect, delayed speech feedback was not superior to the various speech-contingent masking conditions. Modulated masking was more effective than continuous masking, irrespective of delay. The ameliorative effects of DAF therefore appear nonspecific, and models for stuttering based on neural delay loops and the concept of perceptual interference are considered premature.