Imagine scanning a crowd, looking for a familiar face, but everyone has the face of a stranger. That's what happens every time Heather Sellers walks into a restaurant.
"I am known to everybody else, and I don't know if I know them or not," Sellers said.
Some people never forget a face. But for 40 years, Sellers, a college English professor, has never been able to remember one. Even a face she's known since birth.
"I wouldn't be able to recognize my mother out of context if she was walking down the street. And then, along with that, I mistake people for her," Sellers said.
Growing up, Sellers had difficulty making friends. Later in life, not being able to recognize her co-workers, she said, strained relationships and hurt her career.
"I avoided a lot of committee meetings and a lot of my duties at my college, because it was so confusing to go into a room after five years and still not know who these people are," Sellers said.
She avoided parties and social gatherings altogether, because they were torture for her. Amid a sea of faces, she'd have trouble picking out even her closest loved ones.
"I could not recognize my husband, my then-husband, in the grocery store [or] in my own backyard," Sellers said.
Sellers suffers from a neurological disorder called prosopagnosia, or face blindness. The instant someone leaves her sight, the image of that person's face fades from her memory.
It's not that Sellers has a bad memory -- she can recall names, phone numbers, even a book she's read with ease. But mysteriously, she is unable to recall faces. Even her own image in a mirror throws her off.
"There is just a sea of faces that are reflected," Sellers said. "I won't know which one is me. It's frightening, and it's confusing. And I didn't want anyone to know. I thought I was crazy. "
Pretending to Know People
Sellers isn't alone. Jim Heard, a retired art teacher, has spent his entire life pretending to recognize faces when often he can't.
"You hide it. ... You think you're the only person with the problem," said Heard.
"I recognize people -- it's just faces I don't recognize. So I will recognize voices, I will recognize the way somebody walks, all those kinds of little things that you put together that makes a person an individual."
Among the faces Heard struggles to recall are those in his own family. But that problem is shared by other family members. Two of his daughters -- Catherine, an artist, and Jayne, a neuroscientist and mother of two small children -- have trouble recalling his face, too, as well as their mother's.
"It was always common family knowledge that Jayne and my father and I were very bad at recognizing people," Catherine said.
"We'd meet somebody in public, and Mom would have to tell Dad, 'Oh, I think that's one of your students, Jim,'" Jayne added.
Heard said he just thought he was an absent-minded professor. "I didn't have a clue as to why I was like that."
It's not that prosopagnosics have difficulty with vision. They can see faces perfectly well. They just don't know whose face they are looking at, and they won't remember it once they look away.
Nancy Kanwisher investigates visual perception and cognition, and runs a brain research lab at MIT.
"Prosopagnosia subjects can see the face. They know it's a face. They just don't know which face it is. They don't know who it is," Kanwisher said.
Until recently, most prosopagnosia cases that have been studied have been the result of a stroke or a brain injury.
But a new study in the August issue of American Journal of Medical Genetics has found that it's far more common for people to be born with the disorder. Approximately 2 percent, or one in every 50 people, may have some degree of it. Now, researchers say, there may be a single, dominant gene to blame -- a child may inherit prosopagnosia, even if only one parent has it.
It never occurred to Jayne that her face-blindness was something to be alarmed about until the day she went to her son Gabriel's day care center and, to her horror, picked up the wrong child.
"I got a sense that something wasn't right. I picked him up and I took his hood off and I was staring really hard and at that point, I was sort of in a panic and feeling embarrassed, and I eventually had to ask," Jayne said.
Jayne knew something was terribly wrong, but she didn't know what. Panicked and confused, she searched for answers that could unlock the mystery.
Searching for Answers
Desperate for answers, Jayne went online and began researching terms like "facial recognition" and "disorder." She found the Prosopagnosia Research Center at Harvard University, run by Ken Nakayama, a psychology professor.
Nakayama created a number of face-perception tests to diagnose prosopagnosia.
"We have found that prosopagnosics cannot recognize faces. They cannot recognize famous faces very well, like celebrities," Nakayama said.
Within weeks, the entire Heard family underwent a variety of recognition tests, which included recognizing famous faces without the benefit of hair or other features.
The Heards recognized, on average, only 19 out of 60 famous faces, compared with 53 faces recognized by nonprosopagnosics.
After 40 years of self-doubt, with doctors telling her she was depressed and even bipolar, Sellers also finally found Nakayama.
According to Nakayama's tests, many prosopagnosics, like Sellers, can process subtle information about a face, such as whether a face is happy or sad, angry or puzzled. Plus, they can often detect ethnicity, gender and beauty.
But in tests that require a subject to pick out a face in a group, or match a pair of similar faces, Sellers scored poorly. But she said she was relieved to finally be able to put a name on her condition.
Yet much about people born with prosopagnosia remains a mystery.
At MIT, a team of researchers found something startling. They expected born prosopagnosics to be missing the area of the brain that recognizes faces, called the fusiform face area.
But what they discovered is that prosopagnosics not only retain this region of the brain, but it appears to be perfectly normal.
"It leaves us with a real scientific puzzle. Either that region is not functioning normally, or it is working normally and the signal is just not getting out of that region of the brain to other areas where it needs to go," Kanwisher said.
What's even more confounding is the signal affects only faces. Catherine, an artist, can't paint a face from memory, but she can paint Monet's "Water Lilies" in great detail.
"I can visualize a work of art in detail; I can describe it in detail. I sketch it from memory," she said.
We've all had the experience of failing to recognize someone we've met at some point in the past. But, scientists caution, there's a difference -- prosopagnosics make that mistake far more often and with nearly everyone they know.
There's no known cure for prosopagnosia, but for Sellers, just getting the diagnosis changed everything. Now she's no longer ashamed and she comes clean about her condition with just about everyone she meets.