Observed effects of velopharyngeal orifice size on vowel identification and vowel nasality

This study was designed to investigate possible effects of oral-nasal coupling on the nasality of both voiced and whispered test vowels and on the identification of voiced test vowels. One adult subject with cleft palate was fitted with a specially designed speech appliance that permitted alterations in the size of the velopharyngeal orifice. At each of the seven oral-nasal coupling conditions, the subject produced five repetitions of each of two test vowels (/i/ and /u/), first in a whisper and then with voicing. Magnetic recordings of the test samples were evaluated by a panel of nine listeners. The listeners rated the nasality of each sample and, for the voiced vowels, specified the vowel phoneme they perceived each to represent. The results suggest that listeners may be able to scale nasality more reliably for voiced than for whispered vowel samples. They also suggest that nasality and identifiability for vowels may vary complexly as a function of the size of the oral-nasal orifice.