Contribution of facial and vocal cues in the still-face response of 4-month-old infants

The contribution of contingent facial and vocal information in the still-face effect was investigated. Four-month-old infants either saw and heard their mother, only saw their mother, or only heard their mother interacting with them. These interaction periods were followed by the cessation of the mother's interactive face and/or voice. Only infants who observed their mother's face become still and neutral, showed a still-face effect by decreasing their visual attention and positive affect. The findings provide further support that the mother's interactive voice does not contribute to the still-face effect. The developing sensitivity to vocal information in dyadic and triadic contexts is discussed.