Developmental change in auditory preferences for speech stimuli in Japanese infants.

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.