Between ages 6 months and 9 months, a baby accomplishes a heads-up feat, of sorts. That’s when he or she transforms a budding aptitude for detecting animal faces in general into a proficiency at discerning different human faces. This finding bears on the controversial issue of what types of knowledge a baby comes equipped with at birth.
Infants learn to recognize faces through a process that exchanges perceptual breadth for depth, say psychologist Olivier Pascalis of the University of Sheffield in England and his colleagues. By 9 months of age, daily exposure to people has prepped babies’ perceptual system to identify human-specific facial features so that they no longer detect subtle facial differences between members of other species, Pascalis’ group proposes in the May 17 Science.
“Perhaps we’re looking at how innate knowledge about faces changes over time due to visual experience,” Pascalis says. “But it’s impossible to say for sure, since experience with faces begins as soon as a child is born.”
Pascalis’ group had previously observed brain wave changes in 6-month-olds, indicating that the babies recognized previously seen monkey faces even when presented in new orientations. Adults exhibited no brain wave signatures of recognition on this task.
The researchers then conducted face-recognition tests with 60 babies–half 6 months old and the rest 9 months old–and 11 adults. In a series of trials, each participant first viewed the face of a white man or woman and then saw the same face paired with another of the same sex and race. Further trials presented pairs of macaque monkey faces, one of which had just been seen.
Six-month-olds looked much longer at both novel human and monkey faces than at the just-seen faces, a sign the researchers took for both recognition of and preference for the novel images. Adults and 9-month-olds looked longer at new human faces, but not at new monkey faces.
A similar refining of perception also occurs as infants learn native speech sounds, the researchers note. After being able to discriminate between sounds from various languages, babies by age 6 months notice novel sounds solely from their native tongue (SN: 2/8/92, p. 91).
Subscribe to Science News
Get great science journalism, from the most trusted source, delivered to your doorstep.
Early facial and language perception is probably governed by a common “tuning apparatus,” Pascalis theorizes. These skills usually develop together; infants learn to recognize both their mother’s face and her voice by around 2 months of age.
The new findings on facial perception make sense, comments psychologist Paul C. Quinn of Washington and Jefferson College in Washington, Pa. “With enough experience, some types of expertise can develop in infants,” he says.
However, Quinn suspects that face recognition arises from babies’ innate preferences for certain perceptual features, such as curved contours, rather than from more complex innate knowledge about faces, as other scientists suspect (SN: 7/7/01, p. 10: Faces of Perception).
Harvard University psychologist Jerome Kagan agrees. Although the new study highlights the role of experience in face recognition, it’s difficult to pinpoint what an infant knows based solely on increased time spent looking at previously seen faces, Kagan cautions.
With adults, however, face-recognition proficiency appears firmly grounded in human-specific features. Even primatologists who have long studied monkeys prove unable to discriminate between previously seen and new monkey faces, according to an unpublished study by Odile Petit of the Primate Ethology and Behavioral Ecology Center in Strasbourg, France.