This study investigated the developmental patterns of variability in the speech parameter voice onset time (VOT) in forty six children. Five groups of children participated in the study as follows: i) Group 1 -aged 5 years 8 months (n=6); ii) Group 2 -7 years 10 months (n=10); iii) Group 3 -9 years 10 months (n=10); iv) Group 4 -11 years 10 months (n=10), and v) Group 5 -13 years 2 months (n=10). Coefficient of variation (COV) values were examined for the VOT values of both "voiceless" (/p t k/) and "voiced" (/b d g/) plosives to determine patterns of variability. Significant effects of age were revealed for both the voiceless and voiced plosives, and levels of variability leveled off for Group 4. The data suggest that although variability in VOT decreases with age, the presence of residual variability may be a prerequisite for the further refinement of motor speech skills.

Voice onset time (VOT) data for the plosives /p b t d k / in two vowel contexts (/i /) for 5 groups of 46 boys and girls aged 5;8 to 13;2 years were investigated to examine patterns of sex differences. Results indicated that there was some evidence of females displaying longer VOT values than the males. In addition, these were found to be most marked for the data of the 13;2-year olds. Furthermore, the sex differences in the VOT values displayed phonetic context effects. For example, the greatest sex differences were observed for the voiceless plosives, and within the context of the vowel /i/.