ACOUSTIC CUES TO GRAMMATICAL STRUCTURE IN INFANT-DIRECTED SPEECH - CROSS-LINGUISTIC EVIDENCE

Several theorists have suggested that infants use prosodic cues such a s pauses, final lengthening, and pitch changes to identify linguistic units in speech. One potential difficulty with this proposal, however, is that the acoustic shape of an utterance is affected by many factor s other than its syntax, including its phonetic, lexical, and discours e structure. This has raised questions about how the infant could use timing and pitch as cues to any aspect of linguistic structure without simultaneously factoring out other effects. Acoustic analyses of conn ected samples of spontaneous speech addressed to 13.5-14-month-old inf ants by American English- and by Japanese-speaking mothers revealed th at both utterance- and phrase-level acoustic regularities were large e nough to be detected in spontaneous speech without correcting for othe r influences on the same acoustic features. (1) Utterance-final vowels were lengthened and underwent exaggerated pitch changes in both langu ages, and (2) local acoustic changes in duration (English) or pitch (J apanese) were reliably associated with some phrase boundaries within u tterances. These findings suggest that a naive listener could estimate a rough prosodic template for each language based on robust acoustic patterns in observed sentences. We discuss ways in which the learner c ould combine acoustic and distributional analyses across utterances to acquire language-specific variations in prosodic bracketing cues and to obtain indirect perceptual evidence for the internal structure of u tterances.