Phonetic Category Cues in Adult-Directed Speech: Evidence from Three Languages with Distinct Vowel Characteristics

Using an artificial language learning manipulation, Maye, Werker, and Gerken (2002) demonstrated that infants' speech sound categories change as a function of the distributional properties of the input. In a recent study, Werker et al. (2007) showed that Infant-directed Speech (IDS) input contains reliable acoustic cues that support distributional learning of language-specific vowel categories: English cues are spectral and durational; Japanese cues are exclusively durational. In the present study we extend these results in two ways. 1) we examine a language, Catalan, which distinguishes vowels solely on the basis of spectral differences, and 2) because infants learn from overheard adult speech as well as IDS (Oshima-Takane, 1988), we analyze Adult-directed Speech (ADS) in all three languages. Analyses revealed robust differences in the cues of each language, and demonstrated that these cues alone are sufficient to yield language-specific vowel categories. This demonstration of language-specific differences in the distribution of cues to phonetic category structure found in ADS provides additional evidence for the types of cues available to infants to guide their establishment of native phonetic categories. (Contains 2 tables and 8 figures.)