Nonword repetition in children and adults: effects on movement coordination.

Hearing and repeating novel phonetic sequences, or novel nonwords, is a task that taps many levels of processing, including auditory decoding, phonological processing, working memory, speech motor planning and execution. Investigations of nonword repetition abilities have been framed within models of psycholinguistic processing, while the motor aspects, which also are critical for task performance, have been largely ignored. We focused our investigation on both the behavioral and speech motor performance characteristics of this task as performed in a learning paradigm by 9- and 10-year-old children and young adults. Behavioral (percent correct productions) and kinematic (movement duration, lip aperture variability - an index of the consistency of inter-articulator coordination on repeated trials) measures were obtained in order to investigate the short-term (Day 1, first five vs. next five trials) and longer-term (Day 1 vs. Day 2, first five vs. next five trials) changes associated with practice within and between sessions. Overall, as expected, young adults showed higher levels of behavioral accuracy and greater levels of coordinative consistency than the children. Both groups, however, showed a learning effect, such that in general, later Day 1 trials and Day 2 trials were shorter in duration and more consistent in coordination patterns than Day 1 early trials. Phonemic complexity of the nonwords had a profound effect on both the behavioral and speech motor aspects of performance. The children showed marked learning effects on all nonwords that they could produce accurately, while adults' performance improved only when challenged by the more complex nonword stimuli in the set. The findings point to a critical role for speech motor processes within models of nonword repetition and suggest that young adults, similar to children, show short- and longer-term improvements in coordinative consistency with repeated production of complex nonwords. There is also a clear developmental change in nonword production performance, such that less complex novel sequences elicit changes in speech motor performance in children, but not in adults.