ACOUSTIC PROPERTIES THAT DETERMINE ADULTS PREFERENCES FOR 3-MONTH-OLD INFANT VOCALIZATIONS

When videotapes of 3-month-old infants who engaged in social vocalization are presented, the quality of their vocalizations affects the viewing adult's perceived favorableness of infants. In general, adults prefer infants who produce so-called ''syllabic'' as compared with ''vocalic'' sounds. In this study, we attempted to quantitatively determine the acoustic properties that distinguished these two types of vocalizations. Results of our acoustical analysis of Canadian infants reveal that syllabic and vocalic sounds differ from one another in two parameters, duration and degree of nasality of vocalizations. Naturalistic observations of Japanese mother-infant vocal interactions suggest that those acoustical properties indeed differentially affect responses of the mother to infant vocalizations. When listening to those vocalizations that vary in degree of nasality but do not differ in duration, Japanese adults perceive less nasal sounds as more favorable. Adults' preference for 3-month-old infants' vocalizations appear to be determined largely by differences in nasality, and the phenomenon could be cross-linguistically universal.