Differential effects of happy, neutral, and sad still-faces on 2-, 4- and 6-month-old infants

The role of facial expression in the determination of infants' reaction to the sudden still-face of a social partner was investigated. In a within subject design, 2, 4 and 6-month-old infants were tested in periods of normal interaction interspersed with periods of prolonged still-face episodes in which the female adult social partner adopted either a happy, neutral, or sad static facial expression while maintaining eye contact with the infant. Proportion of infants' smiling and gazing at the social partner as indices of reaction from the various still-face episodes reveal that, in comparison with same age control groups, four and six-month-old infants did not demonstrate any differential responses depending on either happy, neutral, and sad still-faced expression. In contrast, two-month olds demonstrated some evidence of a reduced still-face effect in the happy still-face condition. These results point to early developmental changes in the mechanisms underlying the still-face phenomenon. We propose that by 4 months, and not prior, the reaction to still-face episodes are essentially based on the detection of social contingencies. Copyright (C) 2002 John Wiley Sons, Ltd.