“If you have experiences where you often recognise people out of context, that's an indicator. If you’re more likely to recognise someone else than they are to recognise you, then that's an indicator,” says psychologist Richard Russell of Gettysburg College in Philadelphia, who first coined the term ‘super-recogniser’ in a paper he published in 2009. “Many describe not being sure whether to go up to someone – often it’s someone they knew only incidentally, and they fear they may come across as a stalker. Some report just faking not to know people.”

Russell became curious about super-recognisers in 2006, when he was at Harvard University studying prosopagnosics: people with very poor ability to recognise faces. He discovered it was a far more common affliction than he expected; about 2% of people he tested fell somewhere on the low end of the spectrum. “So I thought that suggested there were people on the other end of the scale too – with extraordinary abilities,” he says.

When he started looking, he found super-recognisers across the United States. One of his subjects, Jennifer Jarett, is a 44-year-old police misconduct investigator in New York City. Her first memory of her talent was when she was 15 and on a family vacation in Hawaii. “I spotted a man sitting a few rows ahead on our plane. I told my family he was famous and had been on a tonne of TV shows, like Murder She Wrote and the Bionic Woman. They just laughed at me because no one recognised him,” she says. Later that summer, the man she had spotted, Granville Van Dusen, played a bit part in the show Family Ties. “So it became a family joke. That's when they realised I was unimpeachable when I recognised someone,” she laughs.