Definition reprinted with permission from Hood, Stephen B. (editor) available from Stuttering Foundation of America: Stuttering Words (Publication No 2: Speech Foundation of America)
An interference with perception of a sound or pattern of sounds by simultaneously presenting another of a different frequency, intensity, quality, or pattern to one or both ears of the subject. Masking is usually presented via head phones and is used to interfere with the stutterer's perception of his own voice. The usual effect, especially at sufficiently high levels of loudness, is increased fluency.