What does your infant see when they look at you? Do you appear as just a round blob with some dark features? Or can your child already recognize that they are looking at a face, one belonging to the parent who will love and protect them?
Scientists, philosophers—and parents—have asked similar questions about what is innate and what is learned in the infant brain, going all the way back to the ancients. A study conducted using an apparatus specifically designed to inspect the brains of babies may bring an answer one step closer.
A paper published on November 15 in Current Biology suggests that a patch of cells dedicated to identifying human faces, the fusiform face area (FFA), is up and running in infants as young as two months old. And areas of the brain’s visual system that are specialized for recognizing bodies and scenes also show more activity at that age than areas for other observed objects.
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Rebecca Saxe, a professor of brain and cognitive sciences at the Massachusetts Institute of Technology, and her colleagues scanned 42 infants ranging in age from two to nine months using a special functional magnetic resonance imaging (fMRI) helmet designed specifically for babies. The task was not easy. Data from 16 of the infants had to be thrown out because, as anyone who has been around a baby knows, it is extremely difficult to keep them happy, still and awake for long. For the 26 remaining infants, the scientists compared activity in visual areas of the brain while they watched 2.7-second video clips that depicted faces, body parts, landscapes, objects and abstract swirls.
Results showed higher activity in brain regions dedicated to faces, bodies and scenes, compared with the other categories surveyed in the fusiform face area, the extrastriate body area and the parahippocampal place area, respectively.
“The big surprise of these results is that specialized area for seeing faces that some people speculated took years to develop: we see it in these babies who are, on average, five or six months old,” Saxe says. “That’s a pretty surprising story that pushes back our account of how much the structure of our brain depends on learning and experience.”
Developmental psychologists have debated for decades whether certain human behaviors are learned or innate. The most famous of these disputes has been about language, but the one over visual development is just as intense. The stock answer is that such development is almost always the result of a combination of nature and nurture, but figuring out where that balance lies remains a contentious question.
On one side is a “bottom-up” perspective, dubbed the protomap hypothesis and championed by Harvard University neurobiology professor Margaret Livingstone. It posits that infants first perceive only basic properties of visual input, such as where light is coming from, if the image is sharp or blurry, and whether there are straight edges or curves. These properties are combined to create patterns, and as the child ages, some of these patterns turn up more often than others. For the ones that are especially frequent, the brain starts to dedicate real estate in the cortex to process those patterns and give them meaning.
A contrary “top-down” view was first put forward by Nancy Kanwisher, now a professor of cognitive neuroscience at M.I.T. and Saxe’s former Ph.D. supervisor, one of the discoverers of the FFA in the 1990s. It holds that while some capabilities of the visual system take a long time to develop, the key functions of, say, recognizing faces and body parts are so important that babies develop them much faster—on the order of months rather than years—or may even be born with them.
To Saxe, the new study showing more FFA activity in infants in response to faces than to other objects implies the brain prioritizes faces at a very young age. That suggests other higher-up brain regions, such as the frontal cortex, are telling the visual area to pay attention to faces, which quickly leads to the maturation of the region dedicated to detecting them.
“There’s every reason to think that babies are born expecting and looking for their most important social partners,” Saxe says. “Something in their brain makes them interested in faces actually before they’ve had any experience with faces at all. Babies look toward facelike images from hours after birth.”
Other researchers are not convinced by Saxe’s conclusions. To Livingstone, it is the visual component of the faces presented during the study—a curved shape with fine details presented in the center of the screen (the central visual field)—that the infant FFA is picking up on, not the concept of faces itself.
“I don’t believe that there are face patches present at birth. I believe there are curvy-preferring central visual field regions present at birth and that those will be activated by the kinds of stimuli that they used,” Livingstone says. “I don’t disagree with [Saxe and her colleagues’] results. I disagree with the interpretation.”
Seminal work at Livingstone’s lab has shown that experience and learning are essential for the development of the FFA. If baby monkeys are never exposed to faces, the region does not preferentially respond to them. The cells still fire for face-associated properties (curves in the central visual field), but there is not greater activation in the area for faces, compared with that for hands, for instance.
Saxe acknowledges the need to reconcile the two camps, perhaps radically shortening estimates of the time it takes for humans to learn what faces are. “We can’t be claiming there’s no role for visual experience in learning,” she says. “That can’t be the answer because we know visual experience and learning are necessary. And so it demands a story about the combination of visual experience and learning and whatever these prior biases and inputs are.” She hints that her next paper using scans from the same infants will shed more light on what else could be influencing the FFA’s early development.
To Kalanit Grill-Spector, a psychology professor at Stanford University, who also studies vision in young children, the most exciting part of the new paper is not about this question of learned versus innate development. “I think that [the study] is kind of attempting to address this question, but it doesn’t really provide a definitive answer one way or another,” she says.
Instead what Grill-Spector is struck by is the technological capabilities demonstrated in scanning the brains of babies. “What’s really impressive about [the researchers’] paper is the amount of babies that they’ve scanned and with a lot of new innovations in baby fMRI,” she says. “That’s going to push the field forward.”
