Token-to-token variability in developmental apraxia of speech: three longitudinal case studies.

Variability in the speech production patterns of children with developmental apraxia of speech (DAS) was investigated in a three-year longitudinal study of three children with DAS. A metric was developed to measure token-to-token variability in repeated word productions from connected speech samples. Results suggest that high levels of total token and error token variability and low levels of word target stability and token accuracy characterize the disorder. Overall levels of variability and patterns of change over time differed between participants. Longitudinal patterns were indicative of decreasing total token variability and increasing token accuracy. However, change was not consistently unidirectional for two of the three children in the study, suggesting day-to-day performance differences in addition to within-session variability.