Daliri, A. | Search bioRxiv

bioRxiv2021

Relevance of Auditory Errors Decreases When Errors Are Introduced Suddenly

PurposeWhen the speech motor system encounters errors, it generates adaptive responses to compensate for the errors. We previously showed that adaptive responses to task-irrelevant errors are significantly smaller than responses to task-relevant errors when errors are introduced gradually. The current study aimed to examine responses to task-irrelevant and task-relevant errors when errors are introduced suddenly. MethodWe used an adaptation paradigm in which participants experienced task-relevant errors (induced by formant-shift perturbations) and task-irrelevant errors (induced by formant-clamp perturbations). For one group of participants (N = 30), we applied the perturbations gradually. The second group of participants (N = 30) received the perturbations suddenly. We designed the perturbations based on participant-specific vowel configurations such that a participants first and second formants of /{varepsilon}/ were perturbed toward their /ae/. To estimate adaptive responses, we measured formant changes (within 0-100 ms of the vowel onset) in response to the formant perturbations. ResultsWe found that (1) the difference between adaptive responses to formant-shift and formant-clamp perturbations was the smallest for the suddenly introduced perturbations, and (2) responses to formant-shift perturbations positively correlated with responses to formant-clamp perturbations for the suddenly (but not gradually) introduced perturbations. ConclusionsThese results showed that the speech motor system responds to task-relevant errors and task-irrelevant errors more differently when errors are introduced gradually than suddenly. Overall, the speech motor system evaluates the relevance of errors and uses its evaluation to modulate its adaptive responses to errors.

neuroscience↗

bioRxiv2020

Dissociated development of speech and limb sensorimotor learning in stuttering: speech auditory-motor learning is impaired in both children and adults who stutter

Stuttering is a neurodevelopmental disorder of speech fluency. Various experimental paradigms have demonstrated that affected individuals show limitations in sensorimotor control and learning. However, controversy exists regarding two core aspects of this perspective. First, it has been claimed that sensorimotor learning limitations are detectable only in adults who stutter (after years of coping with the disorder) but not during childhood close to the onset of stuttering. Second, it remains unclear whether stuttering individuals sensorimotor learning limitations affect only speech movements or also unrelated effector systems involved in nonspeech movements. We report data from separate experiments investigating speech auditory-motor learning (N = 60) and limb visuomotor learning (N = 84) in both children and adults who stutter versus matched nonstuttering individuals. Both children and adults who stutter showed statistically significant limitations in speech auditory-motor adaptation with formant-shifted feedback. This limitation was more profound in children than in adults and in younger children versus older children. Between-group differences in the adaptation of reach movements performed with rotated visual feedback were subtle but statistically significant for adults. In children, even the nonstuttering groups showed limited visuomotor adaptation just like their stuttering peers. We conclude that sensorimotor learning is impaired in individuals who stutter, and that the ability for speech auditory-motor learning--which was already adult-like in 3-6 year-old typically developing children--is severely compromised in young children near the onset of stuttering. Thus, motor learning limitations may play an important role in the fundamental mechanisms contributing to the onset of this speech disorder.

neuroscience↗