The development of the still-face effect: mothers do matter.

The Face-to-Face Still-Face paradigm (FFSF) has been used to investigate how infants react to stressful events. However, there is little developmental data on the FFSF effect, and whether it connects to a specific relationship (e.g., to a mother versus a stranger). This prospective longitudinal study aims to evaluate developmental changes in infant reaction to the FFSF presented by the mother or a stranger at 2, 4, 6, and 8 months of age (n=39). Results show that infant negativity was expressed less in relation to a stranger, the identity effect. Results further suggest that from 6 to 8 months of age, stranger induced protest flattens out; whereas mother induced protest decreases. The results are discussed in relation to different theories regarding infant responsiveness.