Vowel duration in mothers\u27 speech to young children

The purpose of this investigation was to determine whether the duration of vowels in mothers\u27 speech to children contributes to the telegraphic nature of young English-speaking children\u27s speech. This was accomplished by determining whether the known duration differences between content words and function words are exaggerated in mother\u27s speech to young children. Fifteen mother-child dyads served as subjects. All children (CA = 1:6-2:4) were female and had a mean length of utterance between 1.00 and 1.40 morphemes. Each mother was asked to read five experimental stories aloud to her child, and to an adult. The stories contained 96 experimental sentences. In these sentences, the content words were examined in phrase-nonfinal and phrase-final positions; the function words in phrase-nonfinal position. The results indicated that content word vowels were longer in child-directed than in adult-directed speech for both phrase-nonfinal (15 ms longer on average) and phrase-final (27 ms longer) positions. Vowel-by-vowel analyses revealed significant effects for each of the four content word vowels employed. The results also showed that function word vowels were only 4 ms longer in child-directed than in adult-directed speech. Word-by-word analyses showed no significant effects for any of the seven function word vowels employed. The 4 ms increase shown for the function word vowels is less than the just noticeable difference (JND) level for speech. In contrast, the increases shown for the content word vowels are probably greater than the JND level. Taken together, these findings indicate that content words--but not function words--might be made more salient in child-directed speech. Thus, the prosodic characteristics of motherese could well contribute to the telegraphic nature of young children\u27s speech. The finding that only content words are considerably longer in mother-to-child speech also suggests that mothers highlight predicate-argument structures when speaking with their children. Thus, the acoustic modifications in child-directed speech may facilitate the acquisition of predicate-argument structure, but probably not the perception and hypothesis of the shorter-duration syllables that serve as grammatical morphemes in English