The ontogeny of face recognition: eye contact and sweet taste induce face preference in 9- and 12-week-old human infants.

Nine and 12-week-old infants (N = 140) who were either calm or crying sat facing a researcher for 3.5 min. The researcher gazed into the infant's eyes with a smiling face or looked above the infant's forehead. She delivered a 12% sucrose solution via a syringe or a pacifier, or she did not deliver anything. After the exposure period, the mother held her infant over her shoulder. Infant gaze direction was recorded while the infant faced the same researcher and a stranger. The confluence of sweet taste and eye contact was necessary and sufficient for calm 9- and 12-week-olds to form a preference for the researcher. Crying infants never did so, even though eye contact and sweet taste arrested crying. Different visual-gustatory combinations induced unanticipated affective states and are discussed within the contexts of cognitive mechanisms that mediate face learning and preference, the proximate mechanisms involved, and the evolutionary significance of face recognition.