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UBC Theses and Dissertations

Prosodic modifications in infant-directed speech Church, Robyn


The purpose of the present study was to compare three prosodic features of IDS with ADS using natural conversation. The three prosodic features examined were duration of stressed content words, duration of unstressed syllables, and rate of speech (both spoken and read). The first objective was to determine the proportion of the slower rate of speech of IDS as compared to ADS that was accounted for by the exaggerated final syllable lengthening in IDS. The second objective was to determine if read IDS is slower than spoken IDS. The third objective was to determine if unstressed function word syllables were shorter in duration than unstressed syllables in content words and if the durations of these unstressed syllables were comparable in IDS and ADS. Two mothers participated in the study. Two 45-minute audio recordings were made for each participant; the first recording session the mother was interacting with her preverbal infant and in the second recording session she was conversing with a familiar female friend. The results showed that IDS was not significantly slower than ADS when the exaggeratedly lengthened final syllable was excluded from calculations of speech rate. This suggests that non-phrase-final content words are not lengthened in spontaneous IDS as compared to ADS. Previous studies showing lengthening of non-phrase-final content words in IDS as compared to ADS were done using read speech. In this study, speech was read at a slower rate than spontaneous speech, which suggests lengthening of non-phrase-final content words is perhaps an artefact of speech that is read to young children. Durations of unstressed syllables in content words were significantly longer than unstressed syllables in function words in both ADS and IDS. However, there was considerable variability for both categories of words resulting in a large area of overlap. Apart from the robust finding of exaggerated utterance final syllable lengthening in JDS, these data showed that the other prosodic features examined were not exaggerated in IDS compared to ADS.

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