I'll take the lead and kick things off, sharing my ideas what I read in various research studies. My ideas that attribute to stuttering: ​ * Perceiving a mismatch between intended/predicted and actual sensory consequences of speech production * Stuttering involves disruption to sensorimotor (and possibly somatosensory) integration * PWS may try to suppress processing of auditory feedback in order to prevent the detection of feedback errors that contribute to speech dysfluencies. This viewpoint predicts a gradual reduction in reliance on feedback with experience of stuttering, as a learnt compensatory strategy * PWS prioritize abnormal early speech-motor activation over external sounds * PWS “learned” to associate their own voice with involuntary motor control, not initiating motor commands, and not activating motor programs * Abnormal speech sound perception may occur when its attention is moved to maladaptive (excessive abnormal) sensorimotor control * Abnormal speech sound perception may negatively affect the “internal” motor timing * Background noise, other people's reactions \[auditory feedback\], and one’s own voice could all be triggers, leading PWS to reduce auditory processing * Compensatory mechanisms to recognize stuttered sounds with the aim of correcting it * PWS who reinforce a speech motor control system that continues to rely purely on feedback control 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 * PWS may reinforce a “monitoring subsystem” detecting excessive errors * Disruptions in corrective commands sent to the articulators * Compensation responses: Unexpected perturbations engage the feedback control system, which supports the online correction of sensory errors during production of the perturbed utterance (aka compensation responses) * Impaired adaptation responses: Sustained perturbations induce sensorimotor learning via the feedforward system, in which there is a gradual updating of stored motor plans based on the consistent errors in sensory feedback (aka adaptation responses) * Disruption in the forward model's comparison between the intended and actual incoming sensory feedback * Disruptions to the normal use of auditory feedback in speech motor control in stuttering * Being error prone to speech motor movements, more motor variability, slower execution, limited improvement with practice. To compensate for these reductions in motor skill, PWS increase dependence on sensory feedback during speech motor control - resulting in placing greater demands on attentional resources, or unstable or insufficiently activated internal models * Making worse use of afferent feedback processing, in the face of faulty modelling of feedback * Disruption to the internal models that facilitate the transformation between motor commands and sensory consequences * Disruption to cerebellar or basal ganglia based learning * 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 * Stuttering involves inaccurate forward predictions of the sensory consequences of a speech gesture - attributed to noisiness (caused by disruption to area Spt (parietal-temporal boundary in the left posterior Sylvian fissure)) in the mapping between an internal estimate of the state of the vocal tract and the sensory system * Stuttering involves weakened feedforward control that leads to an overreliance on feedback control. This is considered a cause of stuttering * The nature of the disruption to the feedforward system may involve either a disconnection of cortico-striatal pathways or a dysregulation of the dopamine system \[due to delayed readout of the motor program\] * Impaired left-hemisphere basal ganglia motor loop. Stuttering is rooted in disruption of the basal ganglia motor loop, from interactions between auditory feedback and the basal ganglia “initiation circuit.” When the basal ganglia detect a match between the current context and that required by an upcoming speech gesture, they signal the SMA to initiate the next phoneme in the sequence * The core deficit in stuttering is in left hemisphere cortical areas involved in feedforward control, which results in small articulatory errors in speech. These errors affect the fluid initiation and termination of speech motor commands by the basal ganglia. Specifically, detection of these errors in auditory feedback means that the current sensory context does not match that required for initiating the next motor program * Disrupted auditory prediction and feedback monitoring. Stuttering involves a disruption in the use of auditory prediction to prime the auditory system prior to onset of a speech movement. A failure to prime may lead to aberrant feedback-driven corrective commands, triggering unnecessary repairs of speech movements * PWS lack pre-speech auditory modulation (PSAM). The auditory evoked potential (AEP) measured in response to an auditory probe is significantly higher when presented during a period of speech motor planning - resulting in enhancement of its sensitivity to auditory feedback, and specifically, to errors in that feedback. Reduced PSAM in PWS reflects a general disruption to prediction of upcoming auditory inputs, whether self- or externally-generated, rather than a disruption to motor command planning. The mechanisms involved in PSAM may contribute more to online feedback-driven corrections, being less involved in longer-term speech adaptation and updating of stored internal models * Placing greater demands on feedback monitoring and error correction * Dysfluencies are the result of the impaired functioning of one of the two control subsystems in isolation; that is, the faulty operation of the feedforward or feedback control system directly causes stuttered speech * 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 * Disruption to the readout of feedforward motor commands leads to the detection of sensory errors in feedback that prevent the proper generation of initiation and termination signals by the basal ganglia