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UBC Theses and Dissertations

Phonological vowel disorders : a case study Pegg, Lauren Jane


The purposes of the present study were: 1) to provide descriptions, both phonological and acoustic, of the vowel system of a child who exhibited a phonological disturbance in his vowel system, and 2) to examine the effects that intervention targeting consonants would have on his vowel system. No specific hypotheses were proposed, although it was implied that there would be some effect. The subject, S, was one of six subjects in a doctoral research study investigating the application of non-linear phonological theory to the assessment and remediation of developmental phonological disorders. The data were selected from the initial assessment session and a reassessment after two blocks of intervention. Both phonological and acoustic analyses of the data were performed. Acoustic measurements included the fundamental frequency and the frequencies of the first and second formants for each phone. The data showed that S had a large phonetic inventory of vowels with a high proportion of vowel errors. Phonemes exhibited considerable variability but one primary phone could usually be identified. Significant in the phonological description were the following: 1) a high front vowel, a back rounded vowel, a low vowel, and a central vowel were among those most accurately produced by S, 2) there were a significant number of errors in the non-high, unrounded phonemes, and 3) /u/ exhibited a high proportion of errors. In general, errors were not sensitive to consonantal context. Acoustically, while the formant patterns for each phone differed from the others, S's vowels were found to be different in some ways from normal. Specifically, the frequency of F2 for his back vowels is higher than expected and the frequency of Fl for /a/ is lower than expected. In addition to some differences in formant frequency, the acoustic data on S's vowels show much more variability than normal. Changes in the data occurred, both phonologically and acoustically, between the pre-and post-treatment assessment Changes included: 1) improvement in the accurate production of /u/, 2) shifts in the phonetic representation of non-high, unrounded vowels, 3) a decrease in random phonemic error, 4) a decrease in the second formant frequency of back vowels and an increase in first formant frequency of /a/, 5) a decrease in variability of both first and second formant frequency, and 6) a decrease in fundamental frequency. While it was possible to describe differences between the pre- and post-treatment data, it was not possible to ascribe these changes solely to intervention. It is difficult to know whether intervention had a direct effect on vowel production or whether the changes which occurred were more general effects of intervention or simply natural events, coincidental with the intervention program.

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