[Research:](https://direct.mit.edu/nol/article/2/2/308/98521/The-Role-of-Sensory-Feedback-in-Developmental) ([PDF](https://direct.mit.edu/nol/article-pdf/2/2/308/1925180/nol_a_00036.pdf)): "*The role of sensory feedback in developmental stuttering: A review*" (2021) **Summary:** Sensory feedback processing is possibly disrupted due to: (1) suppressing the processing of auditory feedback in order to prevent the detection of feedback errors that contribute to speech dysfluencies, or (2) prioritizing abnormal early speech-motor activation over external sounds. Abnormal speech sound perception may occur when its attention is moved to abnormal sensorimotor control. PWS use compensatory mechanisms to recognize stuttered sounds with the aim of correcting it. Such disruptions might then result in (1) reduced Auditory-Vocal Gating (the ability to differentiate between self-generated speech sounds and externally heard sounds), (2) impaired perception of speech sounds, or (3) less current density in the right secondary auditory cortex during the N3 time window. A speech motor control system that continued to rely purely on feedback control, however, would be severely limited in the range of movement speeds it could handle; processing of sensory feedback involves delays of up to 150 ms \[delayed formant transitions\], prohibiting rapid speech movements - resulting in instability in motor control, since feedback-based corrections to ongoing movements are likely to be triggered too late in the speech sequence, leading to overshoots and potentially oscillatory behaviour. To compensate for a reduction in motor skill, PWS increase dependence on sensory feedback during speech motor control, such as slowing the rate of speech. Longer movement durations would allow the system to make better use of afferent feedback processing, in the face of faulty modelling of feedback. Negative result of increased reliance on feedback control: * movements are more time-consuming * placing greater demands on attentional resources * the range of movement speeds that can be dealt with effectively by the system is restricted (i.e., slower movements are favoured) Disruption to the learning, retention, and updating of both types of internal models: Disrupted inverse models will result in inaccurate feedforward motor commands, increasing the need for feedback-based correction of errors. Disruption to forward models will result in inaccurate prediction of the expected sensory consequences of those commands within the feedback control system - increasing production errors, and an impairment in the ability of the feedback system to anticipate and correct for such errors. Faulty forward model predictions could result in generating error signals, triggering a correction of otherwise correctly executed movements. Ultimately, the system will be forced to rely more on a purely afferent feedback control strategy (i.e., reliant on actual sensory feedback without any forward modelling or prediction of that feedback) - resulting in increased instability, due to delays inherent in feedback processing *Overreliance on feedback control.* Max (2004) hypothesizes that stuttering involves weakened feedforward control that leads to an overreliance on feedback control. Unlike in the SMS view, this increased reliance on sensory feedback is not considered to help compensate for stuttering, but instead is a cause of stuttering. Guenther (2020) hypothesizes that stuttering is rooted in disruption of the basal ganglia motor loop, from interactions between auditory feedback and the basal ganglia “initiation circuit.” Other theories propose that it is the interactions between the feedback and feedforward control systems that result in disruptions to fluent speech. It is the operation of the feedback controller on these speech errors that results in dysfluencies. A decreased reliance on sensory feedback over time would presumably also affect the adaptation response; that is, sensory errors would not be incorporated into stored inverse models, leaving feedforward commands unchanged to result in no learning (Chang, 2020).