Individual Differences in Face Processing: Infants' Scanning Patterns and Pupil Dilations are Influenced by the Distribution of Parental Leave.

Fourteen-month-old infants were presented with static images of happy, neutral, and fearful emotional facial expressions in an eye-tracking paradigm. The emotions were expressed by the infant's own parents as well as a male and female stranger (parents of another participating infant). Rather than measuring the duration of gaze in particular areas of interest, we measured number of fixations, distribution of fixations, and pupil diameter to evaluate global scanning patterns and reactions to emotional content. The three measures were differentially sensitive to differences in parental leave, emotional expression, and face familiarity. Infants scanned and processed differently happy, neutral, and fearful faces. In addition, infants cared for by both father and mother (divided parental leave) distributed their gaze more across faces than did infants primarily cared for by one parent (in this study, the mother). Pupil diameter complemented these findings, revealing that infants had larger pupil diameter during observation of neutral emotions expressed by the parent who is not currently the primary caregiver. This study demonstrates how conclusions differ as a function of the particular eye-tracking measure used and shows that the three measures used here converge on the conclusion that 14-month-old infants' processing of emotional expressions is influenced by infants' exposure to fathers and mothers.