The adult face-diet: A naturalistic observation study.

Experience plays a fundamental role in the development of visual function. Exposure to different types of faces is an important factor believed to shape face perception ability. Contents of daily exposure to faces, i.e., the face-diet, of infants have been documented in previous studies. While face perception involves a protracted development and continues to be malleable well into adulthood, an empirical study of the adult face-diet has been lacking. We collected first-person perspective footage from 30 adults during the course of their daily activities. We found that adults' exposure to faces is longer and more diverse compared to that of infants. Frequency of exposure were highest for familiar (75%), own-race (81%), and three-quarter pose (44%) faces. Faces in the adult face-diet were relatively large (median 6°) suggesting fairly close viewing distances. Face sizes were significantly larger for familiar (median 7.1°) compared to unfamiliar (median 4.9°) faces, reflecting the closer viewing distances that characterize social interaction. These results are consistent with the view that face recognition processes are tuned to the ecologically relevant values of face attributes that are encountered most frequently in the real-life context to optimize face perception abilities.