Sidetone amplification, noise, and stuttering.

In the present study, 24 stutterers and 24 matched nonstutterers spoke spontaneously under conditions of quiet, noise (60, 80, 100 dB SPL re .0002 dynes/cm2), and amplified sidetone (0, +10, +20 dB SPL re .0002 dynes/cm2). All 24 stutterers and 23 of the 24 nonstutterers experienced a decrease in vocal intensity from quiet to 20 dB amplified sidetone. All the nonstutterers and 23 of the stutterers experienced an increase in vocal intensity from quiet to 100 dB noise. As a group, the stutterers experienced a significant decrease in stuttering in the noise conditions; however, with regard to the amplified sidetone conditions, only those stutterers who experienced noise first showed a significant reduction in stuttering during amplified sidetone.