The effects of data reduction in determining the schedule of voicing acquisition in young children.

PURPOSE In this study, multiple measures of voicing acquisition were used to evaluate the extent to which developmental patterns based on voice onset time (VOT) mean data differed from those based on token-by-token analyses in typically developing 2-year-olds. METHOD Multiple repetitions of words containing initial /b p d t/ were elicited from 10 English-speaking children biweekly for 4 months. VOT was measured for each stop. For each child, consonant, and recording session, means and ranges were obtained, as were measures of accuracy, discreteness, and overshoot calculated for session means and for individual tokens. RESULTS The token-by-token analyses suggested lower accuracy and more category overlap than the session means and revealed an overshoot phase for all children. They also showed examples of both abrupt and gradual changes that were not always evident in the means. Measures of range, accuracy, discreteness, and overshoot all continued to change after statistically significant VOT differences were observed. CONCLUSIONS The findings suggest that some aspects of voicing development may not be evident in analyses that rely on VOT mean data and patterns of statistical significance. Token-by-token measures provide a more complete picture of stages of voicing development than those based solely on mean VOT values.