| This study was an investigation of voicing acquisition in typically developing children. The research was motivated by the contradictory findings in the literature regarding the acquisition of contrastive voicing. In general, researchers have disagreed about the age at which children develop distinctive voicing categories. Some of the inconsistencies in the voicing literature may have been the result of differences in methodology and data analysis approaches. Therefore, in this study, an attempt was made to re-examine the acquisition of distinct voicing categories, the role of methodology, and the influence of type of data analysis used to determine results. The voicing acquisition of 10 typically developing English-speaking 2-year-old children was examined. The children were recorded every 2 weeks for from 4 to 6 months. Multiple repetitions were elicited for 4 target utterances containing initial /b p d t/. Frequency distributions as well as measures of central tendency and skewness were calculated for each recording session of each child. Additional criteria for assessment of contrastive voicing, including range size, accuracy of VOT productions, overshoot, and discreteness, were also calculated for summary data and full data sets. Overall, the children in this study displayed continuous progress toward the production of distinct voicing categories characterized by a sum reduction in range size, increased accuracy, decreased overshoot overall per target phoneme, and increased discreteness among the voicing categories. The findings of this study support the presence of an overshoot for /p/ and /t/, as previously suggested in the literature, as well as the presence of overshoot for /b/ and many inaccurate /d/ distributions, a characteristic not commonly noted in the existing literature. Furthermore, the differences in findings resulting from the use of mean VOT values or summary statistics in comparison with full data sets, reveals the need to use additional criteria to evaluate contrastive voicing acquisition. |
