About face

How many faces do you know? Hundreds? Thousands? More than you realise, I bet. Consider first your relatives, schoolmates, workmates, neighbours, casual friends. Then there are celebrities, such as film stars, rugby players, tennis stars, even historical figures. Here is a random list: Henry VIII, Beethoven, Nelson Mandela, Winston Churchill, Gregory Peck, Marilyn Monroe, John Lennon, Björn Borg, Salman Rushdie, Princess Diana, Brad Pitt, David Beckham. No doubt I betray my age and cultural habits, but I can picture each one of them. And there are people you simply see around a lot, even though you don’t really know them, but you’d probably recognise them if you unexpectedly saw them on the street in a foreign city.

We also recognise friends and acquaintances after long lapses of time, during which their faces have changed. Hair might have diminished or changed colour, wrinkles increased, chins multiplied, but somehow the same old person shines through. We recognise people whether full-face or in profile, in colour or black and white, laughing or frowning. Just as impressive is our ability to know that we have not seen a particular face before. Walk the streets of London, say, and you might pass hundreds of people and know that you don’t know them, and yet they are all distinctive in their own ways.

These feats are all the more remarkable in that people’s faces don’t actually differ very much. They have two eyes, a nose and a mouth, similarly located on everyone. How can we distinguish, let alone remember, objects that are so alike? Their names don’t seem to be involved. We often remember a face but don’t recall the name, or perhaps don’t even know it, but it’s rare to remember someone’s name but then not recognise them when we see them.

Somehow, then, faces are ‘special’, critical to our sense of belonging and well-being. For this reason, perhaps, a special part of the brain in the temporal lobe, known as the fusiform face area (FFA), has been assigned the task of encoding information about faces, and providing quick information as to whether we know someone or not. Injury to that part of the brain can result in a specific loss of the ability to recognise faces, while recognition of other objects remains intact. This is known as prosopagnosia, vividly described in Oliver Sacks’s book The Man Who Mistook His Wife for a Hat.

In one remarkable study, tiny electrodes were inserted into the temporal lobes of patients to record the activity of single cells (or neurons) from among the 100 billion which make up the bulk of the human brain. The purpose of this was to locate the source of epileptic seizures. In one patient, one particular cell was activated whenever the patient was shown pictures containing the face of the actress Jennifer Aniston. It responded to a wide variety of her poses, but was knowingly silent when Brad Pitt appeared in the same picture. (Aniston and Pitt had recently divorced after five years of marriage.)

As though to compensate for ability to recognise faces under different conditions, there are some transformations which greatly impede recognition. Faces are peculiarly difficult to recognise upside down, unlike most other common objects, such as a bicycle or a tree. Figure 1 depicts a face, but it’s almost impossible to see it as a face unless you turn it around—and even then you might have to work on it a bit. Figure 2 looks recognisable as a smiling Margaret Thatcher, but turn it round and you’re in for a rude shock. The trick here was to leave the mouth and eyes the right way round but turn the rest of the face upside down. This seems to show that eyes and mouth are fairly critical to recognition, but only when viewed the right way up.

Figure 1

Figure 2

Figure 3

Faces, unlike most objects, are almost unrecognisable as photographic negatives. This can be demonstrated with a neat trick. Stare at the four dots in the middle of figure 3 for 20 seconds or so, and then look at a blank wall or sheet of paper. The result is known as a negative afterimage, and in this case you should then see, and perhaps recognise, the face of which figure 3 is the unrecognisable negative.

There is a story, probably apocryphal, of two Oxford professors, who went bathing in the nude in the local river. While drying themselves on the river bank, a boat full of female undergraduates came by. Professor A immediately covered his lower body with his towel, but Professor B covered his face. ‘Why did you do that?’ asked Professor A. ‘Most people,’ replied Professor B, ‘recognise me by my face.’