This research aims to characterize the process by which exposure to the native language results in changes in infants' perception of speech. Properties of the native language sound system affect listeners' perception of speech, a phenomenon that begins during infancy. The proposed studies will form the basis of a research program investigating the interaction of phonetic and phonotactic information in infants' developing language processing system. Experiments 1 and 2 examine the development of familiarity with native language phonetic categories. Experiment 1 asks at what age infants recognize a set of phonetic categories that occur in their language in comparison with phonetic categories that do not occur in the language. Experiment 2 asks the more fine-grained question of whether this developing sensitivity is also present for within-language categories; namely, are infants sensitive to the difference between phonetic categories that occur frequently in their language versus categories that occur with low frequency in their language? Experiments 3 and 4 examine the time course with which infants' developing phonotactic system affects their discrimination of phonetic contrasts. Both experiments compare infants from different language backgrounds (Exp 3, English vs. Japanese; Exp 4, English vs. Spanish) on their discrimination of contrasts that are phonotactically licensed in only one of the two languages. The proposed research is designed to lay the groundwork for a research program examining the interaction of phonetic and phonotactic development. Previous research suggests that both of these aspects of perceptual/linguistic development might arise on the basis of a single computation - a context-specific phonetic learning algorithm. However, before embarking on this research program it is necessary to flesh out our knowledge of the basic time course of development. This data will in turn inform our understanding of the mechanism by which infants' perception becomes attuned to the native language, which provides a foundation from which infants can begin to learn words and grammar. This process exemplifies the ability of the human brain to find structure in the gace of highly variable and noisy input. A fuller understanding of how learners accomplish such a feat may ulitmately lead to advances in the treatment of individuals with disordered language, to more successful methods for second-language instruction, and to the development of better speech recognition systems. ? ? ?
