Speech timing of phonologically disordered children: voicing contrast of initial and final stop consonants.

Speech timing of nine phonologically disordered and nine normally developing children was investigated for the voicing contrasts of word-initial and word-final stop consonants. Measurements of voice onset time, vowel duration, consonant closure duration, and voicing during consonant closure were made from spectrograms. In addition, listener transcriptions were employed for perceptual analysis. Results indicated that some phonologically disordered subjects failed to differentiate VOT in word-initial voiced and voiceless stops, whereas others produced much longer VOTs for voiceless stops than did control subjects. In the word-final voicing contrast, the phonologically disordered children evidenced longer consonant closure durations and less voicing during consonant closure than did normal subjects. However, like normal subjects, they demonstrated differential vowel and consonant closure durations in voiced and voiceless contexts. Perceptual analysis indicated significantly more voicing errors in the initial final stops of phonologically disordered children. These various results are interpreted to mean that some phonologically disordered children may have less mature speech timing control. The implications of these data for the description of voicing errors also are discussed.