Imagine not being able to recognize your mother, your spouse or your own children. Imagine seeing a stranger and realizing it's your reflection.
For people with prosopagnosia, this is part of everyday life.
Prosopagnosia, or face blindness, is an incurable neurological disorder that impairs the ability to recognize faces — even those that should be familiar.
Sometimes the impairment affects only facial recognition, but some people with prosopagnosia also have difficulty identifying objects and places. Many report problems with other aspects of face processing: They find it difficult to distinguish age or gender, understand expressions or follow a person's gaze.
While many people may have trouble putting faces to names, prosopagnosics often can’t recognize someone they've just met. They can’t follow movies or TV shows because characters all look the same. They can’t even recognize their own family members.
Linda Catterall, a prosopagnosic from Scotland, wrote about one such experience inThe Guardian newspaper.
"A young boy ran towards me. He appeared to be the same size and build as my elder son, but as I looked more closely, I realized it wasn't him. I turned away, but he kept running to me, joy and excitement on his face. Then I realized it was my son. I just didn't recognize his face."
It can be difficult to understand how someone can see a familiar face but not recognize it. Brad Duchaine, a Dartmouth College professor who's been studying face blindness for more than 15 years, demonstrates it by taking familiar faces and turning them upside down.
See for yourself: Can you easily identify the well-known people below?
From top left to right: Sandra Bullock, Justin Timberlake, Bill Clinton, Prince Harry, Michael Jordan and Lucy Liu.
"On several occasions I have apologized for almost bumping into a large bearded man, only to realize that the large bearded man was myself in a mirror," he writes.
Sacks says he's learned to identify his reflection because he knows that he has large ears. Prosopagnosics tend to focus on individual parts of faces, so Sacks looks to his ears to determine if the man in the mirror is himself.
Other people with face blindness say they'll make strange faces in the mirror so they know which reflection is their own.
Being unable to recognize people can make socialization difficult. Prosopagnosics can walk right past a friend or co-worker without realizing it, and they worry about being pegged as rude or antisocial.
Depression and social anxiety are common in people with face blindness, but they find ways to cope with their disorder.
They often rely on non-facial information like hair color, gait and tone of voice to distinguish people. However, if a person changes his hairstyle or shaves a beard, that person can suddenly become unrecognizable.
"Imagine walking into a place where everyone looks like identical twins. That’s what I have to go through at social gatherings," prosopagnosic Glenn Alperin told The Atlantic.
Alperin says he doesn’t look at people until they speak to him, and when they do, he'll try to pick up on context clues to figure out if he knows them.
What causes prosopagnosia?
There are only about 100 documented medical cases of face blindness, but researchers at Dartmouth College, Harvard University and University College London say the disorder isn’t that uncommon.
"2.5 percent of the world’s population has the disorder. That’s one person in every 50. That is not rare at all," said Garga Chatterjee, who conducts prosopagnosia research at Harvard.
It's likely you know someone with prosopagnosia even if they don't realize it themselves. Many famous people say they suffer from it, including Brad Pitt and artist Chuck Close.
Some people are born with face blindness. Developmental prosopagnosia often runs in families, and researchers believe it’s caused by a genetic mutation or deletion. Often, people with this type of face blindness don’t realize they have the disorder.
"It’s like colorblindness," prosopagnosic Dori Frame told The New York Times. "You don’t realize you see colors differently than anyone else until someone points it out to you."
Acquired prosopagnosia — when a patient suffers brain damage from an injury or stroke — is better known because patients have a sense of their impairment and remember what it was like to recognize faces.
People with damage to a certain part of the brain often lose the ability to recognize faces, and numerous studies have been conducted that monitor blood flow to brain regions when subjects view faces. Still, how the brain perceives faces remains a mystery.
"Just because you see some part of the brain turn on when you look at faces, it doesn't mean that it’s necessary for face recognition," said Nancy Kanwisher, a scientist at MIT.
Though researchers have searched for cures or even prosopagnosia therapies, none have demonstrated lasting improvements in people with the disorder.
People who never forget a face
At the other end of the spectrum are what scientists call "super recognizers." They have an extraordinary ability to remember people they’ve seen or met only briefly — even after years have passed and the person’s appearance has changed.
Studies of super recognizers are just getting underway, but findings suggest that about 1 percent of people are super recognizers.
Josh P. Davis, a University of Greenwich psychologist, is studying a group of London police officers to see how perceptional ability aids in recognizing faces pulled from security footage.
He suspected some of the officers could be super recognizers after hearing that 20 of them were able to identify more than 600 suspects from grainy images taken from security cameras during the London riots — even though, in many cases, rioters' faces were partially covered.
Davis' tests have confirmed that at least five of the officers are super recognizers. One cop alone accounted for 190 identifications.
Scientists aren’t sure what makes super recognizers' brains so effective at distinguishing details in faces, but one possibility is that their brains are better at holistic processing, or viewing faces as a single unit. People with prosopagnosia see facial features, but they have trouble viewing a face in its entirety.