Acquisition of the voicing contrast language-delayed and normal-speaking children

Voicing is a phonological contrast which emerges early in the speech of children. However, the acoustic correlates of the voicing contrast for stop consonants are fairly complex. In the initial position, voicing is cued primarily by the relative timing of articulatory versus laryngeal gestures. In the final position, the duration of the preceding vowel is associated with the voicing contrast of stop consonants. The purpose of this study was to examine the pattern of acquisition of the voicing contrast in the speech of ten children diagnosed as language-delayed in comparison with the acquisition of the voicing contrast by normal speaking children. The language-delayed and normal-speaking children were matched according to mean length of utterance (MLU) and placed in one of Brown's five developmental stages. Each participant was first given a short test, using natural speech, to determine his or her ability to identify minimal pairs differing in the voicing of stop consonants. Those who passed the test were recorded under standard recording conditions repeating 12 test words. The test words contrasted voiced and voiceless stop consonants in initial and final positions. Spectrograms of the three best productions of each word were used to examine voice-onset time for stops in initial position and preceding vowel duration for stops in final position. Although the language-delayed and normal-speaking children showed equivalent linguistic sophistication (as measured by MLU), the language-delayed children's control of the acoustic-phonetic details of the voicing contrast was less mature than that of the normal-speaking children.