Compensatory speech motor abilities in normal and phonologically disordered children

Abstract

Many researchers have found that adults can compensate for the effect of a bite-block and produce acoustically normal vowels. The purpose of this study was to determine whether normal and phonologically disordered children also demonstrate similar evidence of motor equivalence during speech. Six normal and four phonologically disordered preschool children were tape recorded while they said the words heat, hit, and hat in three conditions: control, with a 10 mm bite-block, and with clenched teeth. The frequency of the first and second formants for [æ] and of the second formant for [i] and [i] were measured. Acoustic effects of the fixed jaw positions were observed for all of the children. Adult listeners were also asked to identify the children's productions of the words and to rate the “typicality” of the vowels, using a three-point equal interval scale. Perceptual effects of the fixed-jaw position vowels were also observed. These results are consistent with the results of other studies which suggest that motor equivalence for speech develops gradually. The formant patterns of two of the phonologically disordered children resembled those of the normal children. The formant patterns of the other two phonologically disordered children, taken together with the results of the perception experiment, indicated aberrant vowel production in both the control and the experimental conditions.