Humans’ unique ability to perceive faces – a process that occurs in the right hemisphere of the brain – occurs much earlier in life than scientists have previously thought, according to researchers from the University of Louvain in France.
“Just as language is impaired following damage to the brain’s left hemisphere, damage to the right hemisphere can impair our ability to distinguish faces so it is critical to understand how it develops,” says co-author Bruno Rossion, of why the team were so interested in identifying at what point this face-recognition ability develops.
Previously, scientists had thought that the ability to perceive faces, which sets us apart from non-human primates, develops as children learn to read, but the study from Rossion and colleagues – published in the journal eLife – suggests that this ability is already “highly evolved” in infants as young as 4 months old.
Older studies had reported that babies seem to have a preference for face-like images over non-face-like images from birth, and that at a few months of age, infants are more likely to pay attention to faces over meaningless patterns.
However, there has been no evidence until now that infants possess the neural systems that confer the ability to place faces in a distinct category of their own.
“Parents and carers are already aware of how quickly babies’ brains develop but, until now, gathering evidence has been hard due to the limitations of the methods used,” says Rossion.
The Louvain team monitored the brain activity of 15 babies using caps fitted with electrodes. In the experiment, the babies were shown a rapid succession of images as they sat on their mothers’ laps, which consisted of 48 images of faces interspersed with 200 images of animals, plants and man-made objects.
Each image was only shown for 166 milliseconds and the images of faces varied in perspective, color, lighting and background.
The researchers found that when the babies saw a picture of a face, there was a corresponding spike in activity in the right hemispheres of the infants’ brains. Interestingly, comparing the results from the infants to the results of the same study conducted in adults, the difference in activity between the right and left hemisphere was even more pronounced in the babies.
Rossion explains that humans far outperform computer algorithms when categorizing visual images:
“Given the enormous resources devoted to digital face recognition, the babies’ brain accomplishment is not trivial. The success of this research method in babies demonstrates that it can be used in all ages to improve our understanding of how we develop the ability to perceive complex images.”
The authors argue that as the face is such a frequent and socially important stimulus across human development that it makes the ideal area of study for attempting to understand how the ability to visually categorize objects develops.
Next, the team will apply the same methods to studying when the ability to tell individuals apart emerges and how this ability develops with age.