Slower and incomplete retrieval of speech motor plans is the proximal source of stuttering: stutters occur when syllable motor plans stored in memory are concatenated to produce the utterance motor plan

Abstract

This paper describes a hypothesis about stuttering that distinguishes between two methods of assembling the speech motor plan for an utterance – speech construction, which involves real-time preparation of the speech motor plan and speech concatenation, which involves retrieval and chaining of syllable motor plans stored in memory. It is hypothesized that stutters are significantly reduced when people who stutter (PWS) speak in novel speaking patterns such as whispering and prolonged speech because these unaccustomed speaking tasks require speech construction. In contrast, when PWS speak in their habitual speech pattern, concatenating syllable motor plans stored in memory, they stutter. Reaction time studies and the effect of word frequency on stutter rate show that PWS are slower in retrieving stored motor plans during speech concatenation. On the other hand, conditions that positively prime the retrieval of motor plans – phonological priming, reading, production of serial speech, speech shadowing, and stuttering adaptation tasks – speed up the retrieval of motor plans and, therefore, reduce the amount of stutters. The slower retrieval of syllable motor plans may lead to an incomplete specification of the utterance motor plan. Stutters result when the articulatory system attempts to execute an underspecified utterance motor plan.