Short-term plasticity in children's speech motor systems.

Speech production is a highly skilled behavior that requires rapid and coordinated movements of the orofacial articulators. Previous studies of speech development have shown that children have more variable articulatory movements compared to adults, and cross-sectional studies have revealed that a gradual transition to more stable movement patterns occurs with age. The focus of the present investigation is on the potential role of short-term changes in speech motor performance related to practice. Thus we developed a paradigm to examine the influences of phonological complexity and practice on children (9 and 10-year-olds) and adults' production of novel nonwords. Using two indices that reflect the degree of trial-to-trial consistency of articulatory movements, we analyzed the first and last five productions of the novel nonwords. Both children and adults accurately produced the novel nonwords; however, children showed a practice effect; their last five trials were more consistently produced than their first five trials. Adults did not show this practice effect. This study provides new evidence that children show short-term changes in their speech coordinative patterns with practice. In addition, the present findings support the contribution of neuromotor noise or background, inherent variability to speech motor development.