Challenging the notion of innate phonetic boundaries.

Numerous studies of infants' speech perception abilities have demonstrated that these young listeners have access to acoustic detail in the speech signal. Because these studies have used stimuli that could be described in terms of adult-defined phonetic categories, authors have concluded that infants innately recognize stimuli as members of these categories, as adults do. In fact, the predominant, current view of speech perception holds that infants are born with sensitivities for the universal set of phonetic boundaries, and that those boundaries supported by the ambient language are maintained, while those not supported by the ambient language dissolve. In this study, discrimination abilities of 46 infants and 75 3-year-olds were measured for several phonetic contrasts occurring in their native language, using natural and synthetic speech. The proportion of children who were able to discriminate any given contrast varied across contrasts, and no one contrast was discriminated by anything close to all of the children. While these results did not differ from those reported by others, the interpretation here is that we should reconsider the notion of innate phonetic categories and/or boundaries. Moreover, success rates did not differ for natural and synthetic speech, and so a minor conclusion was that children are not adversely affected by the use of synthetic stimuli in speech experiments.