Rhythmic Versus Phonemic Interference in Delayed Auditory Feedback

Purpose: Delayed auditory feedback (DAF) of a speaker's voice disturbs normal speech production. Various traditional theories assume that the content of the delayed feedback signal interferes with the actual production of a particular speech unit (phonemic content hypothesis). The displaced rhythm hypothesis as an alternative explanation suggests that speech disturbances arise from a disruptive rhythm that is produced by the delayed speech signal. The present experimental study directly contrasted the role of rhythm and speech content in a DAF task using speech units as stimuli. Method: One hundred fifty-one participants read aloud 4 different sequences of double syllables that varied in phonemic content and rhythm while auditory feedback was either nondelayed or delayed by 200 or 400 ms. Results: In line with previous studies, the authors found a peak of disturbances at a delay of about 200 ms, independent of speech rate. More important, the present results clearly support the displaced rhythm hypothesis. A speech rate dependency of this effect was also found. Conclusion: Rhythm seems to be a significant criterion of speech monitoring, and hence a mismatch between spoken words and auditory feedback realized by DAF induces obvious speech problems on rhythmic level regardless of phonemic discrepancy at the same time.