Normal and reduced phonological space in the production of vowels by deaf adolescents

Abstract

The production of the vowels /i/,/a/,/c/, and the diphthong /ai/ was investigated spectrographically in the speech of 36 deaf and 4 normally hearing adolescents. The phonological space defined by the maximum and minimum values of F1 and F2 is found to be reduced for many of the deaf subjects. This reduction of phonological space is due primarily to a restricted range of F2 and secondarily to a restricted range of F1. The degree of F2 variation bears a significant positive correlation (0.76) to the intelligibility of the subjects' connected speech. It is suggested that the phonological space reduced most noticeably in the dimension of the second formant is due to the abnormal auditory and visual feedback imposed upon the deaf child: the deaf child's frequency sensitivity is typically worse in the region of the second rather than the first formant; the articulatory gestures of tongue movement, which exert a strong influence on the movement of the second formant, are among the most difficult for the deaf child to see. [Supported by NINCDS Grant 03856.]