Changes in variability during intervention for childhood apraxia of speech: implications for therapy.

Typically developing children are variable in their speech production with decreasing variability indicating mastery of speech. Excessive variability which does not change over time may be an indication of unstable motor plans as often seen in children with childhood apraxia of speech (CAS). Dynamic Systems Theory (DST) provides a framework for understanding the role of variability in speech development and disorder. There are few studies that explore the impact of therapy on speech variability. This work explores the impact of therapy on perceptual speech production variability. It is a post-hoc analysis of data collected in two intervention studies of a motor-based treatment approach with children with CAS and explores DST variability effects in speech skill acquisition based on the case data from those studies. There were six participants in total across the two studies. Findings were mixed showing some non-linear changes in variability with larger changes in variability observed in participants who engaged in more extensive therapy. However, the pattern of variability change was not consistent across the participants. These findings suggest that targeting variability in therapy may be an effective way to improve the speech of children with CAS. A model for utilising variability in therapy is presented.