An investigation of vowel organization in speakers with severe and profound hearing loss.

Vowel auditory formant distances were obtained from speakers with hearing loss to investigate how perceptual constraints affect the contrastiveness and intelligibility of their spoken vowels. These distances were evaluated in relation to the 3-Bark critical distance principle for vowel height and place as described by Syrdal (1985) and Syrdal and Gopal (1986). Seven speakers with profound hearing loss, 10 with severe hearing loss, and seven with normal hearing produced the vowels /u/, /i/, /I/, /ae/, /a/, and /--/ in an /hVt/ context. Vowel formants and fundamental frequencies were obtained with acoustic spectrographic and LPC analysis and converted to Bark values to establish auditory formant distances. Confusion matrices were constructed from normal listeners' identifications of recorded vowel productions. When frequency data were transformed to a Bark auditory scale, increasing convergence of vowel targets was obtained with increase in hearing loss. Percent correct identifications of the vowels produced by the three groups reflected speaker group differences seen in vowel contrastiveness/overlap in auditory phonetic space. Four levels of performance based on error incidence and type were determined. F1-F0 by F3-F2 Bark distance coordinate plots of a given speaker's vowel space reflected the differential intelligibility scores shown by confusion matrices of individual speakers from the four performance levels. Vowel organization by speakers with hearing loss was influenced by (a) formant critical distance, and (b) formant audibility. The least audible formants, F2 and F3, showed the greatest effects of severe and profound hearing loss. F1 and F0 showed further change with the most profound losses and revealed individual differences as well.