A phonetic analysis of vowel errors during the course of treatment

The vowel patterns displayed by one phonologically disordered child were evaluated during the course of a 10-week treatment period using a combination of acoustic and transcriptional methods. At the conclusion of treatment the size of the child's vowel inventory and overall vowel accuracy improved. Although the child's vowel inventory increased, a chronological mismatch in vowel mastery occurred, whereby vowels that were expected to be mastered early [i, o, a] were the least accurate, while vowels that were not expected to be mastered [I, ae] were highly accurate. Those vowels with the highest accuracy also showed the most significant acoustic changes with regard to fundamental frequency and vowel duration. Vocal tract resonance measures of formant frequency were not discriminating of changes in vowel accuracy across the course of treatment. Discussion focuses on the nature of vowel development in phonologically disordered children, as depicted along transcriptional and acoustic phonetic domains.