The perceived clarity of children's speech varies as a function of their default articulation rate.

The current study investigated whether variation in children's default articulation rate might reflect individual differences in the development of articulatory timing control, which predicts a positive correlation between rate and perceived clarity (motor skills hypothesis), or whether such variation is better attributed to speech external factors, which predicts that faster rates result in poorer target attainment (undershoot hypothesis). Two different speech samples were obtained from 54 typically developing children (5;2 - 7;11). Six utterances were extracted from each sample and measured for articulation rate and segmental duration. Fourteen adult listeners rated the utterances for clarity (enunciation). Acoustic correlates of perceived clarity, pitch, and vowel quality were also measured. The findings were that age-dependent and individual differences in children's default articulation rates were due to segmental articulation and not to suprasegmental changes. The rating data indicated that utterances produced at faster rates were perceived as more clearly articulated than those produced at slower rates, regardless of a child's age. Vowel quality measures predicted perceived clarity independently of articulation rate. Overall, the results support the motor skills hypothesis: Faster default articulation rates emerge from better articulatory timing control.