Babies Develop Face Recognition through Practice
Scientists have long considered the ability to recognize faces innate for human and primate babies; they just know how to find and fixate on faces immediately from birth. But a new study suggests the only reason babies know how to look at faces is because they have experience face-timing.
Working with macaques temporarily deprived of seeing faces while growing up, a Harvard Medical School team led by neurobiologists Margaret Livingstone, Michael Arcaro, and Peter Schade has found that regions of the brain critical to facial recognition form only through experience and are absent in primates who don’t encounter faces while growing up. (Granted it’s an animal study, but it’s as close as scientists can come to studying humans in this case; what kind of monsters would they be to intentionally deprive an infant of face-to-face contact?)
The finding, the researchers say, sheds light on a range of neuro-developmental conditions, including those in which people can’t distinguish between different faces or autism, marked by aversion to looking at faces. Most importantly, however, the study underscores the critical formative role of early experiences on normal sensory and cognitive development, the scientists say.
Livingstone explains that macaques — a close evolutionary relative to humans, and a model system for studying human brain development — form clusters of neurons responsible for recognizing faces in the superior temporal sulcus (an area of the brain and not, in fact, a Harry Potter spell) by 200 days of age (roughly equivalent to a little more than 2 years for humans). Yet, both humans and primates develop areas in the brain that respond to specific, evolutionarily ‘newer’ visual stimuli, like text as well. And while it’s not clear if all of these regions that respond to different visual stimuli develop at the same time — why would facial recognition be inborn, but something like textual recognition be learned?
Livingstone, Arcaro and Schade raised two groups of macaques. The first one, the control group, had a typical upbringing, spending time in early infancy with their mothers, other juvenile macaques, and human handlers. The other group grew up raised by humans who bottle-fed them, played with and cuddled them — all while the humans wore welding masks. For the first year of their lives, the macaques never saw a face — human or otherwise. At the end of the trial, all macaques were put in social groups with fellow macaques and allowed to see both human and primate faces.
When both groups of macaques were 200 days old, the researchers used functional MRI to look at brain images measuring the presence of facial recognition patches and other specialized areas, such as those responsible for recognizing hands, objects, scenes and bodies.
The macaques who had typical upbringing had consistent “recognition” areas in their brains for each of these categories. Those who had grown up never seeing faces had developed areas of the brain associated with all categories — except faces.
Next, the researchers showed both groups images of humans or primates. As expected, the control group preferentially gazed at the faces in those images. In contrast, the macaques raised without facial exposure looked preferentially at the hands. The hand recognition domain in their brains, Livingstone said, was disproportionally large compared to the other domains.
The findings suggest that sensory deprivation has a selective effect on the way the brain wires itself. The brain seems to become very good at recognizing things that an individual sees often, Livingstone said, and poor at recognizing things that it never or rarely sees.
“What you look at is what you end up ‘installing’ in the brain’s machinery to be able to recognize,” she added.
Normal development of these brain regions could be key to explaining a wide variety of disorders, the researchers said. One such disorder is developmental prosopagnosia–a condition in which people are born with the inability to recognize familiar faces, even their own, due to the failure of the brain’s facial recognition machinery to develop properly. Likewise, Livingstone said, some of the social deficits that develop in people with autism spectrum disorders may be a side effect stemming from the lack of experiences that involve looking at faces, which children with these disorders tend to avoid. The findings suggest that interventions to encourage early exposure to faces may assuage the social deficits that stem from lack of such experiences during early development, the team said.
Justin Vincent and Carlos Ponce, of Harvard Medical School, also contributed to the research, which was published in the journal Nature Neuroscience.