This paper investigates the hypothesis that stuttering may result in part from impaired readout of feedforward control of speech, which forces persons who stutter (PWS) to produce speech with a motor strategy that is weighted too much toward auditory feedback control. Over-reliance on feedback control leads to production errors which, if they grow large enough, can cause the motor system to "reset" and repeat the current syllable. This hypothesis is investigated using computer simulations of a "neurally impaired" version of the DIVA model, a neural network model of speech acquisition and production. The model's outputs are compared to published acoustic data from PWS' fluent speech, and to combined acoustic and articulatory movement data collected from the dysfluent speech of one PWS. The simulations mimic the errors observed in the PWS subject's speech, as well as the repairs of these errors. Additional simulations were able to account for enhancements of fluency gained by slowed/prolonged speech and masking noise. Together these results support the hypothesis that many dysfluencies in stuttering are due to a bias away from feedforward control and toward feedback control. EDUCATIONAL OBJECTIVES The reader will be able to (a) describe the contribution of auditory feedback control and feedforward control to normal and stuttered speech production, (b) understand the neural modeling approach to speech production and its application to stuttering, and (c) explain how the DIVA model accounts for enhancements of fluency gained by slowed/prolonged speech and masking noise.Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers

Studies of normal and disordered articulatory movement often rely on the use of short, simple speech tasks. However, the severity of speech disorders can be observed to vary markedly with task. Understanding task-related variations in articulatory kinematic behavior may allow for an improved understanding of normal and disordered speech motor behavior in varying communication contexts. This study evaluated how orofacial kinematic behavior varies as a function of speaking task in a group of 15 healthy male speakers. The speech tasks included a nonsense phrase with a high frequency of stop consonants, a sentence, an oral reading passage, and a spontaneous monologue. In addition, rate and intensity conditions were varied for the nonsense phrase and sentence. The articulatory positions of the upper lip, lower lip, tongue blade, and mandible were recorded, and measures reflecting (a). average features of individual movements or strokes (i.e., peak speed, distance, and duration) and (b). overall spatial variability of the articulators for each task were extracted, derived, and analyzed. Results showed a number of task- and condition-related differences in speech kinematic behavior. The most prominent result from the task comparison was that the nonsense speech task exhibited larger, faster, and longer movement strokes than the other speech tasks. For some articulators (lower lip and tongue), there were task-related differences in spatial variability. Changes in loudness and rate revealed variation in kinematic measures that were often complicated by articulator identity and task type. The results suggest that an expanded range of speech tasks and conditions may aid in the study of normal and disordered speech motor behavior.

Overall, the results suggest that clarity-related changes in diphthong production are accomplished through larger, longer, but not necessarily faster diphthong-related transitions. The clarity-related adjustments in diphthong production observed in this study conform to a simple model that assumes speech clarity arises out of reduced overlap of articulatory gestures.

This study sought to develop a quantitative kinematic description of tongue movement for liquid swallowing in a group of 12 healthy subjects. X-ray microbeam technology was used to track the positions of six small pellets attached to the tongue and jaw while subjects swallowed water at 2- and 10-mL bolus volumes. A feature common to all subjects was a prominent rostral movement of the dorsal region of the tongue. In addition, all subjects consistently increased the displacement and maximum speed of this tongue movement with increased bolus volume. However, detailed movement analysis showed a variety of tongue movement patterns for the group. This variability across subjects was large enough that it was surprisingly difficult to provide a low-dimension quantitative description of the tongue kinematics during liquid swallowing.

This study was intended to replicate and extend previous findings that (a) during fluent speech persons who stutter (PS) and those who do not (NS) differ in their vocal tract closing movements (L. Max, A. J. Caruso, and V. L. Gracco, 2003) and (b) ratios relating lip and tongue speed to jaw speed increase with stuttering severity (M. D. McClean and C. R. Runyan, 2000). An electromagnetic system was used to record movements of the upper lip, lower lip, tongue, and jaw of 43 NS and 37 PS during productions of a nonsense phrase and a sentence. Measurement and analysis of movement speeds, durations, and ratios of lip and tongue speed to jaw speed were performed on fluent productions of a nonsense phrase and sentence. Statistical comparisons were made between PS with low and high stuttering severity levels (LPS and HPS) and NS. Significant variations across groups in movement speed and duration were observed, but the pattern of these effects was complex and did not replicate the results of the two earlier studies. In the nonsense phrase, significant reductions in lower lip closing duration, jaw closing duration, and jaw closing speed were seen in PS. In the sentence task, HPS showed elevated tongue opening and closing durations. For tongue opening in the sentence, LPS showed elevated speeds and HPS showed reduced speeds. The elevated speeds for LPS are interpreted as a contributing factor to speech disfluency, whereas the reduced speeds and increased durations in HPS are attributed to adaptive behavior intended to facilitate fluent speech. Significant group effects were not seen for the speed ratio measures. Results are discussed in relation to multivariate analyses intended to identify subgroups of PS.