Acoustic correlates and listener ratings of function word reduction in child versus adult speech.

The present study investigated "the" reduction in phrase-medial Verb-the-Noun sequences elicited from 5-year-old children and young adults (18-22 yr). Several measures of reduction were calculated based on acoustic measurement of these sequences. Analyses on the measures indicated that the determiner vowel was reduced in both child and adult speech relative to content word vowels, but it was reduced less in child speech compared to adult speech. Listener ratings on the sequences indicated a preference for adult speech over children's speech. Acoustic measures of reduction also predicted goodness ratings. Listeners preferred sequences with shorter and lower amplitude determiner vowels relative to content word vowels. They also preferred a more neutral schwa over more coarticulated versions. In sequences where ratings differed by age group, the effect of coarticulation was limited to adult speech and the effect of relative schwa duration was limited to child speech. The results are discussed with reference to communicative pressures on speech, including the rhythmic and semantic pressures towards reduction versus the pressure to convey adequate information in the acoustic signal. It is argued that these competing pressures on production may delay the acquisition of adult-like function word reduction.