There are a number of circumstances that may significantly alter stuttering disfluencies temporarily. Examples are speaking in sync with a metronome or when excited. This led many to adopt the hypothesis that over-monitoring to our own speech might be the cause, and thus distraction away from our own speech might be the answer. This was a popular theory when I tested this a long time ago (in the seventies!) by having a number of stutterers and a mathched group of nonstutterers produce of speech samples which were recorded.  Distraction was produced by having the respondents follow a pathway on a rotating drum with a wand that recorded on-track accuracy. The slow drum speed was deemed to be "easy" and a speeded up version was rated as "difficult". Trained raters scored each respondent's speech for disfluencies in eack distraction condition.

The results showed that, unsurprisingly, the stutterers produced more disfluencies than the nonstutterers with a ratio above 6 to 1, but neither group showed any statistically significant difference due to the level of distraction! However, even though actual performance accuracy did not vary across conditions, the stutterers rated the difficulty of these conditions in accord with the distraction theory. That is, the stutterers found it easiest to speak in the easy tracking condition, while the nonstutterers found it easier to speak in the condition that had no distraction effect (positive or negative) at all.

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Source: Thompson AH (1985). A test of the distraction explanation of disfluency modification in stuttering. Journal of Fluency Disorders 10, 35-50.   Click here for a copy.