Why are faces denser in the visual experiences of younger than older infants?

Recent evidence from studies using head cameras suggests that the frequency of faces directly in front of infants declines over the first year and a half of life, a result that has implications for the development of and evolutionary constraints on face processing. Two experiments tested 2 opposing hypotheses about this observed age-related decline in the frequency of faces in infant views. By the people-input hypothesis, there are more faces in view for younger infants because people are more often physically in front of younger than older infants. This hypothesis predicts that not just faces but views of other body parts will decline with age. By the face-input hypothesis, the decline is strictly about faces, not people or other body parts in general. Two experiments, 1 using a time-sampling method (84 infants, 3 to 24 months in age) and the other analyses of head camera images (36 infants, 1 to 24 months) provide strong support for the face-input hypothesis. The results suggest developmental constraints on the environment that ensure faces are prevalent early in development. (PsycINFO Database Record