Implicit and explicit motor learning in children and adults who stutter

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Developmental stuttering is a speech fluency disorder, which typically has its onset in pre-pubescent children. There is significant evidence that speech motor deficits are at the core of the disorder. These deficits, which likely are genetic and neural in nature, are considered fundamental to our understanding of the onset, development and recovery from stuttering. In our previous research, we have investigated the extent to which adults who stutter are deficient in their ability to acquire novel motor skills. Our results have demonstrated that these adults are less proficient than nonstuttering speakers acquiring new speech sequences, even after extensive practice. Early evidence of differences in skill consolidation between the stuttering and nonstuttering adults has suggested that this deficit may reflect both motor execution and motor learning processes. Importantly, our results also have shown clear parallels between deficient performance in both speech and non-speech (finger sequencing) motor skills, supporting the hypothesis that these deficiencies affecting people who stutter are not limited to speech articulation but may reflect a general motor deficit. ***Learning a motor skill is a procedural learning process during which performance improves gradually over many repetitions of the task. This process can be both explicit and implicit. Implicit motor learning refers to learning that is incidental, and in which participants are not aware of what they have learned and of how they perform the task. Explicit motor learning can be intentional, and participants are conscious of their knowledge and can report it. These two learning strategies are suggested to reflect different learning mechanisms that rely on distinct neural substrates. We have hypothesized that both implicit and explicit learning may be involved in the development of stuttering but the relative weight of these two processes has not been investigated. Implicit motor learning clearly is important during the early development of speech and it has been suggested that people who stutter may rely to a larger extent on explicit strategies. In addition, both implicit and explicit learning may be affected by the presence of an unstable sensorimotor speech system. Importantly, it has been proposed that explicit learning relies on the establishment of stable internal motor models. The failure to do so for speech may lead to disrupted speech fluency. Unraveling the unique contributions of implicit and explicit motor learning in the development of stuttering is critical to understanding this speech fluency disorder. The proposed project outlines studies aimed at investigating motor learning skills in children and adults who stutter. The project will contribute significantly to our understanding of the nature and development of stuttering and will inform the ongoing refinement of motor control models for speech.**