Does babbling sound native? Listener responses to vocalizations produced by Swedish and American 12- and...

Previous studies of infants' babbling have reported contradictory results as to the extent and timing of discernible phonetic influences of the ambient language. In the present experiment, five experienced phoneticians were asked to listen for ambient language effects on vocalizations produced by American and Swedish 12- and 18-month-olds (with 8 children in each language and age group), and to motivate their decisions in terms of word or phonetic cue perception. Group results indicated that listeners did not perceive effects of ambient language on pure babbles for either of the two age groups, whereas a clear effect appeared in both age groups given a more liberal definition of babbling. This is taken to suggest that results of ambient language listening tests may depend crucially on judgments of vocalizations' word status. As compared to the group trends, listener responses to individual children's vocalizations did not indicate that a majority of either 12- or 18-monthers were sufficiently native-sounding to be reliably identified on the basis of ambient language. A closer analysis of listeners' use of phonetic cues indicated that one single phonetic property, the grave tonal word accent, was discerned by most listeners in vocalizations produced by the Swedish 18-monthers; this property was also discerned by one listener in vocalizations produced by Swedish 12-monthers. This result is consistent with the generally held belief in the primacy of tonal features in phonetic acquisition, and with experimental evidence indicating that Swedish mothers tend to enhance word accent contours in baby talk. In the final section of the paper, the results are discussed with a view to reconcile competing theories of babbling development, notably the 'babbling drift' and the 'independence' hypotheses.