Vowel areas of children with and without dysarthria

By C.M. Higgins and M.M. Hodge

Vowel quadrilateral areas, based on first (F1) and second (F2) formant measures of /i/, /a/, /ae/ and /u/, were determined from words produced by 6 three year-olds, 6 five year-olds and 6 young women, all with normal speech production, and 6 five year-old children with dysarthria. The subjects’ F1 x F2 vowel areas were used to test hypotheses about 1) effect of age on vowel area in Hz and log_n Hz scales, 2) effect of dysarthria on vowel area, and 3) relationship between speech intelligibility and vowel area. Our results were in agreement with previous research that has shown that vowel area, expressed in Hz², decreases as age increases. When vowel areas using a log_n Hz scale were compared, the three year-olds had significantly larger areas than the women. This was unexpected as it was predicted that the log_n Hz scale would normalize vocal tract size differences for vowels [Nearey, 1992]. Vowel areas of the children with dysarthria were significantly smaller than their age-mates without dysarthria, largely due to a reduction in F2. A moderately strong positive correlation (r= .71) was obtained between vowel areas and scores on a single word intelligibility test for the 12 five year-old children.