The perception of speech naturalness of post-therapeutic and altered auditory feedback speech of adults with mild and severe stuttering.

The effect of therapy and altered auditory feedback (AAF) on the perception of speech naturalness of people who stutter was examined. Thirty-five naive young adult listeners rated speech samples from fluent speakers and individuals who stutter. Samples came from normal adults who spoke Standard American English; adults with mild or severe stuttering who spoke under conditions of non-altered feedback (NAF), delayed auditory feedback (DAF), and frequency-altered feedback (FAF); and adults with mild or severe stuttering prior to and following successful completion of a Precision Fluency Shaping Program. Speech produced under AAF was rated as significantly more natural sounding than speech from the same individuals under NAF (p < 0.0001). Speech produced during FAF was judged to be more natural sounding than that produced during DAF for those with mild (p = 0.003) and severe (p < 0.0001) stuttering. Mild stuttered speech was judged to have more natural-sounding speech than severe stuttered speech during AAF (p < 0.0001). Speech from individuals following therapy was rated significantly less natural sounding than that from individuals during AAF for both mild and severe stuttering (p < 0.0001). The speech of individuals prior to therapy was rated significantly more natural than their speech produced after therapy (p < 0.0001). Speech from normal fluent speakers was rated as significantly more natural sounding than all samples produced from the individuals who stutter (p < 0.0001). These findings support the contention that AAF benefits those who stutter through a reduction of stuttering with a gain in perceived speech naturalness.