Speech Rate Modification and Its Effects on Fluency Reversal in Fluent Speakers and People Who Stutter

A theory has been proposed recently that asserts that the problem that people who stutter have arises when these speakers attempt to execute speech at a faster rate than planning processes allow. This leads speakers to complete words before the following one is ready. Plan unavailability usually happens on the more complex content words rather than the relatively simple function words. There are two ways of dealing with this situation when it arises. Speakers can (1) delay production of a content word by repeating prior function words or (2) carry on and attempt to produce the following content word and gamble that the remainder of the plan arrives while it is being executed. The former strategy does not lead speakers to persist in their dysfluency, while the latter does. It is proposed that the pressure on speech rate that leads speakers to adopt the latter strategy is particularly acute around adolescence. In this article two experiments are reported which test the effects of rate on fluency. In Experiment 1, fluent speakers are induced to produce stuttering-like dysfluencies on content words using a commentary task. A prediction of the theory is that procedures known to induce fluency have to produce local slowing of speech so that planning and execution can get back in synchrony. This prediction is confirmed for frequency-shifted feedback and when speakers who stutter have to sing in Experiment 2. Results are discussed in terms of the model for the etiology of stuttering based on plan unavailability. The implications of the results are also discussed with respect to the diagnosis of the disorder and how it can be treated.