Children's vowel acquisition has long been examined on the basis of transcription-based evaluations of the accuracy rate of the vowel production in children before 5 years of age. This study examines the development of static and dynamic acoustic features in children between 3 and 7 years of age by comparing the acoustic features of children with those of adults. All acoustic analyses were based on the normalized formant frequency values to exclude the effect of different vocal tract size. The increasing compactness of individual vowel categories in the acoustic space evidenced the refinement of phonetic features in children in this age range. In addition, the vowel dispersion pattern of certain vowel plotted on the basis of formant frequency values at 5 temporal locations demonstrated positional change as well as differences in terms of the trajectory length. Results demonstrate that the acoustical development of vowels from children to adult norms is likely a long-term, graduate but not necessarily continuous process.
Bibliographic reference. Yang, Jing / Fox, Robert Allen (2013): "Acoustic development of vowel production in American English children", In INTERSPEECH-2013, 1263-1267.