“Actually, I just had an experience today,” said Marlene Behrmann, a cognitive neuroscientist at Carnegie Mellon University who has spent decades studying the science of facial recognition.
She went to meet a colleague outside the hospital where they collaborate, and didn’t realise the person was sitting right in front of her, wearing a mask. In fairness, “She’s cut her hair very short,” Behrmann said.
Scientists have some ideas about why masks make recognising others’ faces difficult, based on studying the brains of average people, as well as people who struggle to recognise anyone at all. But even when everyone around us is incognito, we still have ways to find each other.
“We use face recognition in every aspect of our social interaction,” said Erez Freud, a psychologist with the Centre for Vision Research at York University in Toronto. In the faces of others, we find clues about their personality, gender and emotions. “This is something very fundamental to our perception. And suddenly, faces do not look the same,” Freud said.
That’s why Freud and co-authors decided to study how masks impair people’s facial recognition skills. They recruited nearly 500 adults to complete a common face memory task online. Participants viewed unfamiliar faces and then tried to recognise them under increasingly difficult conditions. Half the participants saw faces with surgical-style masks covering their mouths and noses.
People scored substantially worse on the test when faces were masked. The authors posted their findings, which have not yet completed peer review, online last month.
Authors at the University of Stirling in Scotland posted a similar study in June that also has not yet been through peer review. In that study, 138 adults completed online face-matching tests. When the scientists superimposed masks onto the faces, people performed worse — even when the faces belonged to familiar celebrities.
In Freud’s study, 13% of participants struggled so much to recognise masked faces that they may as well have suffered from prosopagnosia, or face blindness. Without masks, only 3.5% scored that low.
In the general population, prosopagnosia may affect about 1 in 50 people. Some have face blindness their whole lives; others develop it suddenly after trauma to the brain.
Just because you’re tripped up by face masks doesn’t mean you have true face blindness. Still, “People have got a little sense of what it means to be affected,” Behrmann said.
She added that for most adults, face recognition is an extremely sophisticated process that happens almost instantaneously. That’s especially true when we see people we know well. “Because it’s so good, it’s sometimes hard to get a window in to understand how it works,” she said. So scientists have gained much of their understanding of face recognition by studying people with prosopagnosia.
Other studies have tested people without face blindness. Researchers have challenged subjects’ powers of recognition by presenting faces upside-down, or faces entirely obscured except for one feature, or half-and-half creations of celebrities, such as George Clooney’s mouth and nose fused with Robin Williams’ eyes.
One of the main takeaways has been that facial recognition happens holistically, or all at once. We don’t scrutinise people’s features piecemeal. Rather, we take in the entire face in a glance. When half the face is hidden by a mask, the process suffers.
But all is not lost. Research has shown that out of all facial features, we rely most on the eyes to recognise people. Even if we struggle to know who we’re looking at when only their eyes are visible, we may still pick up information about a person’s identity and emotions. “A lot of information is conveyed by the eye region,” said Richard Cook, a psychologist at Birkbeck, University of London. “We’ve still got access to that information.”
“We also use other cues, and we can fall back on some of those other cues if they are helpful,” Behrmann said. For example, we might recognise people by the way they walk or talk, or by their facial hair or hairstyle (except for Behrmann’s recently trimmed colleague). Prosopagnosics may rely on these external cues already.
The observer’s culture may matter, too. In what researchers call the “headscarf effect,” study participants from Egypt and the United Arab Emirates, where women often cover their hair, outperformed British and American participants at identifying faces when only the eyes, nose and mouth were showing.
In some Asian countries, wearing masks in public to protect against viruses was commonplace before COVID-19. Might people in those parts of the world be more comfortable recognising each other with their faces covered?
“It is indeed an interesting point,” said Katsumi Watanabe, a cognitive scientist at Waseda University in Tokyo.
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