Iris, the Greek goddess of the rainbow, carried the first messages from the gods to man; 3,000 years later, the flow of communication is to be reversed. There are plans afoot, as we learned this week, to harness our irises, those pretty rings of multicoloured muscle in our eyes, to reveal our identities to the Olympians of Homeland Security.

We’ll each need to earn notoriety first: the FBI’s data-sharing proposals, involving an entire suite of biometric data, are directed at catching major criminals and terrorists. The name the Feds gave this project, however, suggests that someone, somewhere, is looking to the future: “server in the sky”. This is either a tip of the hat to 80s rock band Doctor and the Medics’ only hit or, more likely, a grotesque piece of security-state triumphalism.

Mind you, we are all more than likely to offer up our eyes over the next couple of years to any institution that cares to stare into them. Iris scanning is set to replace the passport and credit card as the preferred method of proving identity. Who wouldn’t want to pass through Heathrow in a blink, after all?

But there is something unpleasant about the idea of having one’s eyes scanned, and this is not altogether the fault of the film Minority Report’s stolen eyeballs scene. It is more to do with our intuition that the eyes are windows on the soul. The human eye is built to be noticed. Simply opening the eyes wider can, with other facial movements, express everything from shock to arousal to doubt. Simple gaze direction conveys emotional meaning. The lateral rectus eye muscle is labelled “amatoris” in early anatomies because lovers use it to direct their flirtatious glances.

Eyes reveal our inner state. It is impossible to control our rate of blinking for any length of time, or the way our pupils wax and wane. When aroused, we blink more often, and our irises dilate. Our eyes, with their bright whites, colourful irises, responsive pupils, brows and lashes, have evolved to communicate and carry meaning.

Nonetheless, given the amount of information they carry, eyes are surprisingly hard to read. We don’t count each other’s blinks, and we don’t press our faces up against each other to study the changes in each other’s irises. Of course, we don’t have to: we have language – which lets us lie in a way the eyes don’t. But liars are easy to spot – aren’t they?

Humans have been pack animals for most of their history. When survival depended on cooperation there was little advantage to be had from blatant lying. In a tightknit community, a pathological liar stands to lose too much if they are caught out. Now, things are different. A 65-year-old, Jean Hutchinson, was sent to jail for five years this week. Why? From her secret operations room, accessed through a wardrobe, she had managed to impersonate 76 different people well enough to defraud the British state of £2.4m.

Technology confers anonymity on people far more effectively than it establishes identity. The biometric security market emerged in the US following the passing of two laws. Neither had anything to do with security, the war on terror or other bugaboos. One was the health insurance act of 1996, which made healthcare firms protect their clients’ records more carefully; the other, known as Sarbanes-Oxley, was meant to reduce the fiddling of financial records after the collapse of Enron.

The war on terror is a branding exercise. The war on fraud is real. The technology has a long way to go before machines are invented that can scan our eyes for the secrets of our hearts. Still, this is the path we are on. As our machines learn more about us, we are increasingly learning how to hide behind our machines.

Guardian, Thursday 15 March 2007

Like those jingles you can’t stop humming, some bad ideas stick. This one has maddened me for years: when you and I see a green ball, do we see the same green? When we have toothache, we don’t all have the same toothache. The notion that pain varies between individuals does not disturb us. Why, then, do we resist the idea that different people see different colours?

Just as you and I, each suffering our own very different toothaches, can agree on what a lousy experience toothache is, so we can all roughly agree on what colour is what. We can argue till the cows come home whether this particular shade of turquoise is green or blue, but we both pretty much agree on what green and blue are. There is a lawfulness to colour, and it would help if we knew where this lawfulness resided.

In his 1995 essay The Case of the Colour-blind Painter, the neurologist Oliver Sacks describes the case of an artist who, through subtle but devastating damage to his brain, could not see colour. Though damage of this sort robs an individual of the experience of colour, the mechanisms of colour vision continue to function. Asked to match up coloured counters, people with no experience of colour are still able to match up colours perfectly. They just don’t see them. But if the relationship between wavelength and colour is purely contingent, where the devil do colours come from?

Artists are forever trying to uncover universal meanings behind their colours. It is easy to scorn their efforts, not least because this kind of thinking dates very quickly. Kandinsky’s experiments in colour symbolism may as well have been conducted in the 14th century for all their relevance now. There is, none the less, a growing body of evidence that colours, shapes, sounds and smells do have meanings. Wolfgang Köhler’s delightfully simple 1929 experiment asked volunteers to match a pair of abstract figures to one of two nonsense words, “maluma” and “takete”. Immediately, and virtually without exception, people matched maluma to the soft round figure and takete to the sharply angular one. Some sort of shared symbolism related the sounds to the shapes.

Now Dr Jamie Ward, at University College London, might have uncovered an underlying symbolism to colour. Ward’s interest is synaesthesia – the experience of a handful of individuals who perceive information through an unexpected sense. Some hear colours, others smell shapes. The vast majority see sounds. The experiences of individual synaesthetes are notoriously idiosyncratic. But there are unexpected regularities, and Ward’s bulging address book – he knows 450 synaesthetes by name – allows him to spot trends that were formerly invisible. For example, among synaesthetes who see coloured letters, A is often red, B is often blue, and C is often yellow. “This is likely to hold true for other types of synaesthesia,” Ward says, “assuming that we are able to make a large enough number of observations. For instance, certain musical instruments may tend to produce particular colours, shapes and movements.”

Synaesthesia may simply be an exotic manifestation of something we all enjoy: the ability to turn sensations into symbols, and to think with them. After all, if our thoughts are not made of sensations, what are they made of? And this is why we find it so distressing, you and I, to realise that we don’t see the same colours. Colours – so striking, so beautiful, so manifestly there – are one of the few things we can agree on, more or less. How cast adrift will we feel if colours turn out to be, after all, only our thoughts about light?

Human colour vision is a relatively recent acquisition. It is, at most, 63 million years old, and it may be a lot younger. On a genetic level, it is a mess: misalignments and redundancies in the genes that code for our “red” and “green” colour perceptions account for 95 per cent of all variations in human colour vision, and it is quite usual for up to nine genes to cluster together in an attempt to code for these colours. This is why the perception of colours – especially blues and greens – varies so much between individuals. Humans perceive colour through three types of colour-sensitive cell, called cones, but some have four types. Equipped with four receptors instead of three, Mrs M – an English social worker, and the first known human “tetrachromat” – sees rare subtleties of colour. Looking at a rainbow, she can see 10 distinct colours. Most of us only see five. She was the first to be discovered as having this ability, in 1993, and a study in 2004 found that two out of 80 subjects were tetrachromats.

If our eyes did not move – if they simply “drank in” the view before them – we would go blind. Our retinas can only process contrast, and soon become exhausted looking at the same thing for too long. They must tremble constantly in order to bring still objects into view.

Human vision captures only two degrees of the world with any clarity, so we tend to miss things that happen outside our focus of attention – and the more we concentrate, the more extreme our “attention blindness” becomes. This makes us easy prey for psychologists such as Daniel Simons and Christopher Chabris, whose notorious experiment of 1999 asked its viewers to score a three-a-side, 90-second basketball game. Afterwards, the viewers were told to relax, put down their score cards and watch the video again. Only then did the game’s most remarkable feature come to light: the invasion of the court, a few seconds in, by a 7ft-tall pantomime gorilla.

Our eyes stay several steps ahead of us, whatever we happen to be doing. When negotiating a turn in the road, for example, a driver’s eye will provide motor information to his or her arms almost a second before he or she makes any movement. By then, the eyes will already be looking elsewhere. Visually at least, we operate in the world not as it is, but as it existed half a second ago. This raises a not insignificant question: how does the eye know where to direct its gaze next?

The concept of a bionic eye is nothing new. In the 1970s, bio-engineer Paul Bach-y-Rita, now at the University of

Wisconsin-Madison, was turning different parts of the body into eyes. His prototypes were vests containing hundreds of mechanical vibrators. Pixelated images from a low-resolution video camera, worn on a pair of glasses, were translated into mechanical vibrations against the skin of the chest or back. Bach-y-Rita’s volunteers were able to recognise faces using the system. Proof that they could see came when Paul threw balled-up papers at them: they ducked.

Because light behaves differently in water and air, land-adapted human vision is lousy in water. Someone, however, forgot to tell the Moken – gypsies who ply the Burmese archipelago and Thailand’s western coast. Moken children, who spend days diving for clams and sea cucumbers, can see twice as much fine detail underwater as European children. While the pupils of the latter expand underwater, in response to the dimness of the light, Moken pupils shrink to their smallest possible diameter, improving acuity underwater. Mokens also use the lenses of their eyes more, squishing them to the limit of human performance.