Yoko Shimura

Listener and context dependency in the perception of emotional aspects of infant voice

Developmental aspects of an infants ability to express emotions through vocalizations were studied based on perceptual rating experiments against 12 vocalization‐ and emotion‐related reference words. Three groups of listeners, students, mothers with infants, and nursery governesses, rated 28 voice samples recorded from a male infant at 6, 9, 12 and 17 months of age, under a positive or negative context. Among three factors extracted by a factor analysis, one representing the emotional contrast of frightened/angry versus happy was found to be independent of listener group, infant age and context. The other two, one representing contrast between pleased/happy versus demanding/sad and the other seeking affection and rejecting/angry were dependent on infant age and context. These results may indicate that infants even at 6 months of age can express the emotional contrast of ‘pleasure’ versus ‘discomfort’ through vocalization, which listeners perceive independently in context.

The acoustic characteristics of infant cries

The present study measured the acoustic characteristics of infant cries. Twenty‐eight infants participated, ranging from 2 to 23 months of age. Crying was elicited when their mother moved to a distance, leaving them in the lap of unknown person. The cries were recorded with a microphone placed 1 m from the infant’s mouth in an anechoic room. Analysis of the recorded cries revealed four patterns: cries were classified as either voiced or breathy, and as higher or lower than 7 kHz. Certain cry characteristics were later rated as more stress‐causing, suggesting they could potentially elicit more abuse reactions. The recorded cries were presented to adults and breathy cries with a high‐frequency component were labeled as emergency cries and as likely to cause high stress levels in parents and caregivers. In Japan, living spaces have recently begun changing such that environments are more echoic, perhaps exacerbating negative reactions to high‐frequency components of infant cries.

Adult attribution of the infant vocalizations

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.

Development of infants’ expression and perception of emotion through vocalization

Voice samples produced by six infants at 6, 9, 12, and 17 months of age were perceptually evaluated by 79 adults (aged 20–22) and 31 children (aged 2–6) using 9‐point‐rating dipole scales representing emotions. The following results were obtained. (1) Both the adult and child listeners perceived rich contents of emotions from the voice samples recorded even at 6 month of age. (2) More factors were extracted from the rating scores given by the children than by the adults via factor analyses, though many characteristics of the extracted factors were common between the two listener groups. These results indicate the following. (1) Even 6‐month‐old infants who have not yet developed a language can produce voice necessary for emotional communication through nonlinguistic elements of voice. (2) Children are more sensitive in perception of emotions from infants’ vocalization than the adults. Children seem to perceive richer emotions from infants’ vocalizations than the adults.