Stuttering is a neurological problem where the brain and the speaker's OWN voice get disrupted. If you speak with another voice the stuttering will usually be greatly diminished. This is why we stutter much less when we whisper, when we sing and when we speak in unison with another person. This is also why we stutter less when we use a fake accent, speak in a falsetto, etc. This is also the basis for successful stuttering programs which emphasize speaking from the diaphragm and other breathing techniques. It is also the basis for successful stuttering devices like the Edinburgh Masker and Delayed Auditory Feedback (DAF). As long as we do not hear our own voice our stuttering will usually show a dramatic decrease.