Have you ever had a friend totally blank you even though you were sure they looked right at your face?
Maybe they didn't actually see you, maybe they secretly hate you, or maybe they have something called prosopagnosia, also known as face blindness.
Prosopagnosia is a cognitive disorder that means some people struggle to recognise faces – sometimes even those of people they know very well (including themselves!).
"You often hear the phrasing 'I'm really bad with names', but when you think about it, being bad with names is actually having difficulty putting a name to a face," says Dr Punit Shah, a psychology lecturer at Anglia Ruskin University. "Everyone has this to some extent, nobody's perfect, but some people seem particularly bad at being able to do this, and that seems to be what prosopagnosia is."
Around 1 in 50 people in the UK have it. Most cases are developmental, which means people are born with or develop this inability to recognise faces, rather than acquiring it after an accident.
People with face blindness tend to come up with coping mechanisms – relying on someone's voice, their clothes, or something else to work out who they are.
To be properly diagnosed with face blindness involves an in-depth face recognition test. But Shah and his colleagues have come up with a 20 question test that he says provides a good indication of someone's ability to recognise faces. Their test was published today in the Quarterly Journal of Experimental Psychology.
You can take the 20-question test here. Ready?
Try to answer as honestly as you can for the best results. A new question will appear once you select each answer.
If you want to get in touch with Dr Shah or take part in his research, go to his website.
Kelly Oakes is science editor for BuzzFeed and is based in London.
Contact Kelly Oakes at email@example.com.
Got a confidential tip? Submit it here.