It's hard for me to walk into a room without embarrassing myself. Only the other day, I was at a residential conference where I'd eaten breakfast with a group of fellow participants. I went back to my bedroom before heading to the auditorium. Plonking myself down next to a stranger, I smiled, stuck out my hand and said, "Hi. I'm Mary Ann Sieghart." "I know," he replied. "We've just spent the past half-hour talking to each other."
It was mortifying - but this is, I'm afraid, the story of my life. A life spent suffering from prosopagnosia, commonly known as face blindness.
It's not that I can't tell two faces apart when they're next to each other; it's that my memory struggles to store them. So the next time I see someone, the chances are that I'll have no idea who they are, or even whether I have met them before - even half an hour before. My nightmare, which occurs too often, is being asked: "Do you two know each other?" How would I know?
This is different from forgetting people's names - we all do that as we get older. For those who remember faces automatically, picture this: suppose you've spent an evening playing bridge with three strangers. You've been looking at their hands for hours as they hold their cards. Next time you meet them, their faces are covered and you are asked to recognise them by their hands alone. Could you do it? No? That's my problem in a nutshell.
I'm not alone. Roughly one in 50 of you reading this will suffer from face blindness, too, in varying degrees. Mine is only moderate, so I can recognise family, old friends and at least some colleagues. My mother and one of my daughters (yes, it often runs in families) have a more severe form. Some people are so badly afflicted that they can't recognise their own children, their spouse or their parents.
Imagine not being able to pick out your toddler at the nursery. Imagine being the child who can't recognise its father at the school gate. My daughter once caught sight of a red-faced, sweaty girl in a nightclub, wearing an overly low-cut dress. She was judging her rather too harshly when she realised it was herself in the mirror!
Some people, like me, have suffered from face blindness all their lives. Others acquire it via a head injury or a brain illness. It's through studying this acquired form of prosopagnosia that scientists have isolated the area of the brain - the fusiform gyrus, just behind the right ear - that deals specifically with facial processing.
We know it's not just a question of a lack of visual awareness. When psychologists test for prosopagnosia, they show people nine faces (shorn of their hair, which makes it much harder), and then mix those faces in with others. You have to identify the ones you've seen before. They then do the same with houses and horses. On the faces, I scored worse than the bottom 1 per cent of the population. With houses and horses, I was in the top 25 per cent. Send me off hunting, and I'd only be able to recognise my fellow riders by their mounts.
There are many worse disabilities than face blindness, of course, but it can lead to dreadful social faux pas. I'm constantly blanking people I know, which of course offends them hugely. This upsets me, as I set a lot of store by good manners. Worse, most of the time I don't even know that I've hurt their feelings - which is one reason I've made a programme for BBC Radio 4 about prosopagnosia, called Who Are You Again? It's a giant apology to them, and to all the other unintended victims of face blindness who think that we prosopagnosics don't care about them or are even deliberately snubbing them.
Almost every day of the week, I get myself into a pickle. Only last weekend, I failed to recognise my own niece because she'd changed her hair colour. We rely heavily on hair, glasses, beards, voices, height and gait to compensate for our lack of face recognition, so a change in one of them throws us out completely.
I even made the mistake once of offending my boss. I was making my way along a row of theatre seats when a woman came towards me smiling, and sat down next to me. I put on my glassy smile, as I had no idea who she was. Only when I recognised her voice did I realise that she was my managing editor, whose office was only a hop and a skip from mine. Out of context, I was lost.
It didn't help that she had a nicely symmetrical face. The odder or the uglier someone is, the easier I find it to remember them. I'm hugely grateful for a crooked nose, a prominent mole or bad skin. When I meet someone, I will try to store a description in my head, which will go something like this: tall, balding, watery blue eyes, bushy eyebrows, bad teeth. It may sound harsh, but it's the flaws that help me to identify people.
This is why prosopagnosics often find films difficult to follow. Famous actors all look roughly the same to us. Because their faces are symmetrical and flawless, they have no distinguishing characteristics. Hence we often can't remember which character is which - and it's even harder if they're wearing uniforms in a war movie or a police drama.
Luckily, I can manage with someone as distinctive as Stephen Fry, whom I interviewed for this documentary. He is face blind, too, though it's somewhat mitigated by him being allowed to call everyone "darling" on set. As a female political journalist, that might have got me into trouble...
I also talked to Patricia Hewitt, the former Labour Cabinet minister. She used to dread bumping into fellow MPs in the Commons corridors, who'd impart a juicy piece of political gossip. Not knowing who they were made the political intelligence she received almost worthless. At least as she became more senior, she could have a parliamentary aide slipping her the names of her colleagues as they rose to speak in the chamber.
Sadly, there's no cure for prosopagnosia, and most of us can't afford to hire an assistant to whisper into our ear. We sufferers live in hope that a gadget will be invented that will identify faces for us. Already there's a clunky one on the market, consisting of glasses with an inbuilt camera and a speaker that fits into your ear. But it's almost more obvious and embarrassing to use than failing to recognise someone in the first place.
So, in the meantime, I try to hone my dissembling skills. I warn most people I meet that I might not recognise them next time - and that they shouldn't take it personally.
They always do, though. For what's more painful than being overlooked or ignored?
Until prosopagnosia becomes better known, it's almost easier to pretend that I'm short-sighted and have forgotten my glasses. At least myopia is a condition that people understand.