Acquisition of vowel contrasts in Dutch

The aim of this research is to disentangle the contributions of anatomical development of the vocal tract and articulatory learning to the acquisition of vowel contrasts. Four groups of subjects were selected: normal 2-year-olds, normal 4-year-olds, 4-year-olds with a delay in phonological development of approximately 2 years, and adults. Elicited renditions of three Dutch vowels, /u/, /a/, and /a/ were acoustically analysed. The F1 and F2 values of the two vowels constituting a large contrast (/a/ versus /u/) were significantly different in all subject groups. On the other hand, the extent to which the spectra of /a/ and /a/ differed appeared to be affected by age. The 2-year-olds, in contrast to the normal 4-year-olds and adults, produced nondistinctive F2s for these two vowels. The results from the phonologically delayed 4-year-olds paralleled those of the 2-year-olds, which suggests that the acquisition of subtle vowel contrasts is primarily dependent on articulatory learning, rather than the purported anatomical development of the vocal tract.