Delayed Auditory Feedback (D.A.F.), sometimes known as delayed side-tone, is the name given to the technical process in which a subject's speech is recorded, delayed, amplified and returned to his ears through a headphone at such power as to prevent him hearing it through the normal channels of direct air and bone conduction. This process has been found to produce marked disturbance of speech, the main changes found being the production of an artificial stutter, marked slowing of speech, increase in loudness of speech and development of a flatness of intonation or decrease in vocal intensity variation (Lee, 1950/1951). The slowing and increase in intensity have been found by Black (1951) to be related to the variation in delay and amplification, but even when these factors are held constant there is considerable individual variation in the response to D.A.F.