ABSTRACT
This chapter argues that the physiological factors underlyingly constrain the developmental characteristics of the primary vowels and provide preliminary analyses and explanations using the quantitative theory. The development of the main acoustic features of primary vowels in early childhood phonetic acquisition reflects both the robustness of human language systems and the variations restricted by biomechanical constraints. The chapter examines the relevant experimental results and discusses the primary vowels from the basis of the development of fundamental frequency, the development of formants, and the development of acoustic space for the nine different age groups. Through the analysis of the absolute value of F0 in regard to the acquisition of different vowels in the young children groups, it is shown that the three vowels are equally affected by constraining factors, such as age and gender, in terms of duration and level of impact.
