The acquisition of unrounded vowels in English

This study investigated developmental patterns of acquisition of the unrounded American English vowels /i, I, e, e, ae, a/ by following 6 normally developing children from 22 to 30 months of age. The subjects were examined at approximately 22, 26, and 30 months of age. Results showed that, in general, /i/ and /a/ were mastered early and /I/ and /e/ were least accurate throughout the period of the study. Upon inspection of errors, the following three classes of production errors were identified: (a) intertrial production variability, (b) context-sensitive substitutions, and (c) context-free systematic substitution patterns, or articulatory processes. A decrease in production variability and in the occurrence of articulatory processes with age generally coincided with a gradual improvement in accuracy of production. However, substitutions of lower vowels for /I/ were persistent, and the pattern was observed even at 30 months of age. Individual variation was also evident in the production accuracy, the substitution patterns, and the manner of articulatory improvement.