Patterns of developmental change in phonetic perception are critical to theory development. Many previous studies document a decline in nonnative phonetic perception between 6 and 12 months of age. However, much less experimental attention has been paid to developmental change in native-language phonetic perception over the same time period. We hypothesized that language experience in the first year facilitates native-language phonetic performance between 6 and 12 months of age. We tested 6-8- and 10-12-month-old infants in the United States and Japan to examine native and nonnative patterns of developmental change using the American English /r-l/ contrast. The goals of the experiment were to: (a) determine whether facilitation characterizes native-language phonetic change between 6 and 12 months of age, (b) examine the decline previously observed for nonnative contrasts and (c) test directional asymmetries for consonants. The results show a significant increase in performance for the native-language contrast in the first year, a decline in nonnative perception over the same time period, and indicate directional asymmetries that are constant across age and culture. We argue that neural commitment to native-language phonetic properties explains the pattern of developmental change in the first year.

The developmental change in auditory preferences for speech stimuli was investigated for Japanese infants aged 4-14 months old. We conducted three experiments using two speech pairs in the head-turn preference procedure. Infant-directed (ID) speech and adult-directed (AD) speech stimuli were used in a longitudinal study (Experiment 1) and a cross-sectional study (Experiment 2). Native (Japanese) and non-native (English) speech stimuli were used in a cross-sectional study (Experiment 3). In all experiments, infants demonstrated a developmental change in their listening preference. For the ID/AD speech pair used in Experiments 1 and 2, infants show a U-shaped developmental shift with three developmental stages: Stage 1, in which very young infants tend to prefer ID speech over AD speech; Stage 2, in which the preference for ID speech decreases temporarily; and Stage 3, in which older infants again show a consistent preference for ID speech. For the native/non-native speech pair, there is a tendency for an increased preference for native speech over non-native speech, although infants did not demonstrate a U-shaped pattern. The difference in developmental pattern between the two types of speech pairs was discussed.

Regional cerebral blood flow was measured in six healthy volunteers by positron emission tomography during identification of speaker and emotion from spoken words. The speaker identification task activated several audio-visual multimodal areas, particularly the temporal poles in both hemispheres, which may be involved in connecting vocal attributes with the visual representations of speakers. The emotion identification task activated regions in the cerebellum and the frontal lobe, suggesting a functional relationship between those regions involved in emotion. The results suggest that different anatomical structures contribute to the vocal identification of speaker and emotion.

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