Stuttering: Imagining a Solution to the Riddle

The old saying by Van Riper (with a nod to Winston Churchill), that stuttering is a riddle wrapped in a mystery inside an enigma, is well known. While it would be preposterous for any of us to state that, 40 years later, we now have solved the riddle, we can say with a great degree of confidence that advances in scientific inquiry have brought us closer to understanding the factors that may trigger the onset, development, and/or maintenance of stuttering. Nevertheless, much still needs to be learned, because the riddle still poses many challenges. For instance, we do not fully understand why developmental stuttering starts somewhere between 2 and 9 years of age, but onset after puberty is rarely if ever seen (other than neurogenic stuttering, but that is a different story), or why boys are more likely to develop chronic stuttering than girls are. Another unsolved question is the variability seen in stuttering severity. Individuals who stutter often will report having more stuttering in some situations than others, or when talking to some listeners, or even simply from day to day. Similarly, someone with very severe stuttering typically will not stutter on more than approximately 40% of their words. So, what happens with or during the other 60%? And while we have learned a lot about treatment efficacy for children and adults who stutter, we still cannot explain why some clients do well in maintaining their fluency following treatment, while others relapse. These are only a few of the questions that remain to be answered. Over the past 10 to 15 years, my colleagues and I slowly have chipped away at some of the facets of the riddle, as have many other researchers across the world. In this article, I will share some of our findings and the tentative conclusions we have drawn so far. In the following sections, I will review three main themes in our research: (a) people who stutter have a reduced ability to incorporate proprioceptive feedback in their movement execution, (b) people who stutter demonstrate difficulty acquiring new motor skills, and (c) behavioural differences in sensory and motor skills between stuttering and nonstuttering individuals may be related to distinctions in their functional and structural organization of the cortical and subcortical processes. The Role of Proprioceptive Feedback in Stuttering One of the central tenets in the research efforts of my colleagues and I has been that stuttering can be understood best as a speech motor disorder (De Nil, 1999a) while still acknowledging the potential influence of language (Sasisekaran & De Nil, 2006), psychological