Hypernasality Severity Analysis in Cleft Lip and Palate Speech Using Vowel Space Area

Vowel space area (VSA) refers to a two-dimensional area, which is bounded by lines joining F1and F2 coordinates of vowels. In the speech of individuals with cleft lip and palate (CLP), the effect of hypernasality introduces the pole-zero pairs in the speech spectrum, which will shift the formants of a target sound. As a result, vowel space in hypernasal speech gets affected. In this work, analysis of vowel space area in normal, mild and moderate-severe hypernasality groups is analyzed and compared across the three groups. Also, the effect of hypernasality severity ratings across different phonetic contexts i.e, /p/, /t/, and /k/ is studied. The results revealed that VSA is reduced in CLP children, compared to control participants, across sustained vowels and different phonetic contexts. Compared to normal, the reduction in the vowel space is more for the moderate-severe hypernasality group than that of mild. The CLP group exhibited a trend of having larger VSA for /p/, followed by /t/, and lastly by /k/. The statistical analysis revealed overall significant difference among the three groups (p < 0.05).