Dept. of Educ., Saitama Univ., 255 Shimo-Okubo, Urawa-shi, Saitama, 338 Japan
Univ. of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113 Japan
Adult attribution of the infant vocalizations was investigated by perceptual rating experiments for 717 voice samples recorded from seven infants at 2, 6, 9, 12, and 17 months of age. Perceptual rating was performed using nine vocalization- and emotion-related reference words by 15 normal heating adult listeners. By a principal factor analysis, three factors representing the emotional contrast of crying/frightened/sad versus laughing/pleased/happy, shout/surprising versus secret-talk/calm, and speaking versus singing were studied. Even at 2 months of age, significant individual differences were observed in the extracted factor scores, although three were less variability compared to those obtained from the elder infants' vocalizations. These results suggest that the ability to express emotion through vocalization seems to be developing during the observed months of age, although infants even at 2 months of age can express some aspects of emotion through vocalization.