The development of expert face processing: are infants sensitive to normal differences in second-order relational information?

Sensitivity to second-order relational information (i.e., spatial relations among features such as the distance between eyes) is a vital part of achieving expertise with face processing. Prior research is unclear on whether infants are sensitive to second-order differences seen in typical human populations. In the current experiments, we examined whether infants are sensitive to changes in the space between the eyes and between the nose and the mouth that are within the normal range of variability in Caucasian female faces. In Experiment 1, 7-month-olds detected these changes in second-order relational information. Experiment 2 extended this finding to 5-month-olds and also found that infants detect second-order relations in upright faces but not in inverted faces, thereby exhibiting an inversion effect that has been considered to be a hallmark of second-order relational processing during adulthood. These results suggest that infants as young as 5 months are sensitive to second-order relational changes that are within the normal range of human variability. They also indicate that at least rudimentary aspects of face processing expertise are available early in life.