Spectral and cepstral properties of vowels as a means for characterizing velopharyngeal impairment in children.

This study investigated spectral differences in the phonation of vowels between a group of 21 children with velopharyngeal impairment and a paired control group of 42 subjects. The speech material was composed of the isolated vowels /a/, /i/, and /u/, a sustained vowel /a/, and four vowels included in spoken words: two nasals /in/ and /on/ in "dindon," and two orals /a/ and /o/ in "gâteau." A bottom-up discriminant function analysis indicated that the cepstrum coefficients and the linear-FFT were the most efficient tools in the test to classify the set of children. They were superior to the results obtained with the formant-representation of the vowels. The use of a perceptive scale (barks) did not improve the results. Discrimination over the total group showed percentages lower than those obtained when boys and girls were assessed separately. The best discriminating results were obtained with the /a/ of "gâteau" for the girls and with the isolated /i/ for the boys.