Stuttering: a disorder of movement.

Based on the data and discussion in the two preceding papers a preliminary model for disfluency is proposed. Stuttering is identified as movement patterns associated with perceptually judged disfluencies. It is suggested that the speech structures operate within certain ranges of variability in terms of their movement parameters and interarticulator temporal and spatial relations. This variability may be influenced by emotional, perceptual and/or physiological events. When the "normal" ranges are exceeded, the afferent nerve impulses generated alter the gains of associated brainstem reflexes. Altering of the reflex gains throws the articulatory system out of balance and a breakdown in behavior occurs, often manifested as oscillations or static positioning. The influence of physiological and environmental variables on neuromotor processes leading to these patterns is emphasized. The model suggested has been developed from inferences from movement patterns of the upper articulators. Thus, the patterns discussed involve these structures. It is suggested, however, that an understanding of the many behaviors associated with stuttering will be understood only by analyzing the behavioral and neurophysiological interactions among the respiratory, laryngeal, and supraglottal structures.