Approval and disapproval: infant responsiveness to vocal affect in familiar and unfamiliar languages

In a series of 5 auditory preference experiments, 120 5-month-old infants were presented with Approval and Prohibition vocalizations in infant-directed (ID) and adult-directed (AD) English, and in ID speech in nonsense English and 3 unfamiliar languages, German, Italian, and Japanese. Dependent measures were looking-time to the side of stimulus presentation, and positive and negative facial affect. No consistent differences in looking-time were found. However, infants showed small but significant differences in facial affect in response to ID vocalizations in every language except Japanese. Infants smiled more to Approvals, and when they showed negative affect, it was more likely to occur in response to Prohibitions. Infants did not show differential affect in response to Approvals and Prohibitions in AD speech. The results indicate that young infants can discriminate affective vocal expressions in ID speech in several languages and that ID speech is more effective than AD speech in eliciting infant affect.