Kitamura, C. 1 , Burnham, D. 1 , Lee, C. 2 & Todd, N. 3
1 MARCS Institute, University of Western Sydney
2 University of London
3 University of Manchester
Infant-directed speech (IDS) is used in most languages and cultures. Compared to adult-directed speech (ADS), it is characterised by a range of exaggerated prosodic and phonetic features, including higher pitch and wider pitch excursions, slower tempo and hyperarticulated vowels. These features not only assist infants in many of the challenges of early speech perception but also serve an attentional/affective function in mother-infant interactions. The goal of this study was to examine rhythmic cues in IDS using a corpus of Australian English mothers speaking to their infants at birth, 3, 6, 9 and 12 months, and to another adult. Two alternate hypotheses were tested. According to the exaggeration hypothesis, strong-weak stress patterns in English will be exaggerated in IDS for didactic purposes, e.g., word segmentation. Alternatively, according to the developmental hypothesis, stress-based rhythmic cues (as found in English) will be less evident in IDS than ADS, but become more evident as the infant develops. The hypotheses were tested with two methods of rhythmic analysis, one based on a phonetic model, which focuses on measures of durational variability of vocalic and consonantal intervals, e.g., ?V, ?C, nPVI-V rPVI-C; and the other method based on prominence-based theory, which claims the fundamental determinant of a language?s rhythmic structure is variability in prominence of its vocalic/sonorant segments, and focuses on measures such as ?Pson, ?Psyll, rPVI-Pson, rPVI-Psyll. Neither phonetic nor prominence-based models supported the exaggeration hypothesis. According to the phonetic model, there were no differences between IDS and ADS. However, the results of the prominence-based analyses supported the developmental hypothesis and revealed that compared to ADS, suprasegmental cues to stress are reduced in IDS to very young infants but increase from birth to 12 months. We suggest this is due to the overriding importance of the affective/social and mood-regulation roles of IDS in infancy.