Unstable or Insufficiently Activated Internal Models and Feedback-Biased Motor Control as Sources of Dysfluency: A Theoretical Model of Stuttering

This article presents a theoretical perspective on stuttering based on numerous findings regarding speech and nonspeech neuromotor control in individuals who stutter in combination with recent empirical data and theoretical models from the literature on the neuroscience of motor control. Specifically, this perspective on stuttering relies heavily on recent work regarding feedforward and feedback control schemes; the formation, consolidation, and updating of inverse and forward internal models of the motor systems; and cortical, subcortical, and cerebellar activation patterns during speech and nonspeech motor tasks. Against this background, we propose that stuttering may result when producing speech (a) with unstable or insufficiently activated internal models or (b) with a motor strategy that is weighted too much toward afferent feedback control. We discuss how these two hypotheses can account for the specific dysfluencies that form the primary characteristics of stuttering, and we suggest that the hypotheses are compatible with several of the phenomena associated with the disorder (e.g., age of onset, fluency-enhancing conditions, treatment effects). For one of the hypotheses, we also describe a computer simulation implemented in the DIVA (directions into velocities of articulators) model---a neural network model of the central control of speech movements.