An apparatus is described providing an auditory feedback masking noise of variable amplitude and mean frequency, triggered by means of a throat microphone switch and therefore independent of subject control. Evaluation tests of this device made on 53 stammerers demonstrated its effectiveness in reducing stammering and in abolishing gross concomitant movements. Repeated tests on one subject over a period of 22 weeks produced no discernable improvement of hk general speech although, when in use, the apparatus maintained its effectiveness throughout this period. Tests on jive independently diagnosed clutterers demonstrated a significantly reduced response to auditory feedback masking as compared with stammerers.