Speech kinematic variability in adults who stutter is influenced by treatment and speaking style

Aim: We tested whether completion of the Comprehensive Stuttering Program (CSP) is associated with a reduction in speech kinematic variability relative to pre-treatment when adults who stutter (AWS) use a casual speaking manner or fluency skills. Rational: Kinematic variability is higher in AWS suggesting a sensorimotor vulnerability; however, it is not clear whether high variability is a trait related to the underlying disorder or reflects the mutable state of stuttering. Speech restructuring intervention such as the CSP could support more consistent articulatory control and stable movement patterns. Methodology: Thirteen AWS were tested before and after completing the CSP while 11 adults who do not stutter (AWNS) completed a single session. Participants were instructed to use a casual manner of speaking in the first post-treatment session. In the second post-treatment condition, the AWS employed their fluency skills at a control speaking rate. An optical tracking system captured lower lip movements while participants spoke two English phrases and a complex nonword. Across-utterance kinematic variability was measured using the spatiotemporal index (STI) and within-utterance variability was measured with recurrence quantification analysis (RQA). Results: There was a positive treatment outcome based on significant reductions in percentage syllables stuttered (%SS) during speaking and reading, decreases in stuttering severity and improved perceptions of stuttering and communication confidence. The STI of the AWS decreased significantly after treatment for both speaking styles. The RQA variables indicated that AWS used a less stereotyped and more flexible manner of speaking in the casual condition after treatment, but speech movement regularity increased when using fluency skills. Conclusions: The AWS showed a significant decrease in labial kinematic variability alongside a successful treatment outcome involving speech restructuring and cognitive behavioral techniques. These changes in across-utterance and within-utterance kinematic indices demonstrate that effective stuttering treatment can promote speech motor stability along with fluent speech.