Abstract:
Research has shown that exposure to a specific language alters infants' perception of vowel sounds by 6 months of age. Language spoken to infants may exert an important influence on the development of language-specific patterns of vowel perception. This study compares the acoustic structure of vowels produced by ten American mothers in conversation with their infant and another adult. In both conversations, mothers were instructed to use seven words which contained either /i/, /u/, or /a/ (``bead, sheep, boot, shoe, pot, sock'' and ``top''). Results indicate that mothers consistently increased the degree of acoustic separation between vowel categories in their speech to infants, in comparison with their speech to adults. It is speculated that the acoustic structure of vowels in motherese speech contributes to infants' acquisition of native-language vowel categories by increasing between-category acoustic differences and by highlighting the features that distinguish these vowels. Currently an attempt is being made to confirm whether this pattern is universal in infant-directed speech with collaborators in Sweden and Russia. Preliminary results suggest that the expansion of the ``acoustic envelope'' seen in American mothers' speech to infants holds cross-linguistically. [Work supported by the Social Sciences & Humanities Research Council of Canada and NIH.]