19

Telling left from right

After one of his first days at school, our younger son proudly showed us what he had achieved that day. He had printed the entire alphabet, along with the digits from 0 to 9. They were beautifully rendered, but there was just one problem. Each character was written backwards, and the sequence ran from right to left on the page.

Left-right confusion is ubiquitous, especially among young children learning to read and write. The mirror-image letters b and d are often confused, as are p and q, and children may also have difficulty distinguishing words like was and saw or dog and god. Mum and dad remain relatively unambiguous, although dad can sometimes be bad. Many adults also have difficulty distinguishing their left from their right, as in identifying which hand is which or in giving or receiving directional instructions. As a platoon leader in secondary school cadets, I once gave a sharp ‘left turn’ command to the platoon, which banged them straight into a cricket sightscreen. I meant to say ‘right’. No one was hurt, but I was duly demoted.

In the 1920s and 1930s, the influential American physician Samuel Torrey Orton proposed that left-right confusions were the source of reading disability. As a testimony to this, American author Eileen Simpson wrote Reversals, in which she chronicled her lifelong difficulty with left and right, and her struggle with dyslexia. The Orton Society was established internationally to promote Orton’s ideas, but it is now recognised that dyslexia can have other causes, and the Orton Society eventually morphed into the International Dyslexia Association.

Left-right confusion is a consequence of a tendency to treat left-right mirror images as the same. This is generally adaptive in the natural world, which is largely indifferent to left and right. Things are just as likely to happen one way round as the other. Predator or prey may lurk on either side, and the same face or body may appear in either left or right profile. Even the letters b and d are really the same, as you can tell by viewing either of them from the other side. It is this indifference to left and right that explains the bilateral symmetry of the body. Our eyes, ears, arms, legs and so on are symmetrically placed so we can be equally aware of what’s happening on either side, and respond accordingly. Even the brain is largely symmetrical.

But we need some asymmetry if we are to distinguish left from right. By ‘distinguishing left from right’ I don’t mean simply responding asymmetrically to an asymmetrical input, as when we follow a winding road, or reach for an object on one or other side. I mean the ability to interpret left-right mirror images in symbolically different ways, as in calling the letter b a ‘bee’ and the letter d a ‘dee’, or in correctly turning left or right on verbal command. We would be unable to respond in these ways unless we had some built-in asymmetry, which could be as trivial as a mole on one hand, or as complex as an asymmetry in the brain itself.

It is really only in the artificial human world that we must learn to treat left and right as symbolically distinct. In reading most scripts, for example, the orientation of the symbols and the direction in which they run on the page are critical. We must also learn which side of the road to drive on, and some cultures insist that we use the right hand for many social activities, like shaking hands, saluting or eating—or not to do so, as in a certain toiletry procedure, which is the case in some cultures.

The brain seems to have a built-in tendency to record events both in the orientation in which they actually occurred, and as though mirror-reversed. The reversed version is usually weaker, but may still intrude to create confusion. Patients with brain injury sometimes persistently write backwards, or find it easier to read reversed script than normal script. In one report, a Russian woman with right-sided brain damage drew a map of Russia in reverse.

My fellow researcher Ivan Beale and I suggested that the tendency to treat mirror images, like b and d or p and q, as the same may be due to how the two sides of the brain communicate with each other. Thus if one side of the brain learns that the letter b is a ‘bee’, it transmits the reverse information to the other side, which then learns that a d is a ‘bee’. This reversal has been demonstrated in monkeys and pigeons—for example, if one side of the pigeon brain learns that pecking a right-sloping line (/) brings reward, the other side receives the information that a left-sloping line (\) does the trick. This can further explain why a left-sided brain injury can result in mirror-writing—the right side reverses what the left side has learned. Conversely, in the Russian woman who drew the map in reverse, the left side of the brain may have reversed the map that had been recorded correctly in her now-damaged right brain. In order to avoid left-right confusions in learning to read, then, children may have to establish the dominance of one side of the brain, usually the left, over the other, so that reversed habits don’t intrude. Orton recognised that poorly established dominance was one of the factors underlying reading disorders.

Perhaps, then, it is this process of what Beale and I termed interhemispheric reversal that explains our tendency to record events both as they happened and as left-right reversed. This is a nuisance when learning to read, but adaptive in the real world of our forebears. Suppose one was attacked by a dangerous lion from the right, but was lucky enough to escape. If one simultaneously records the event as though the attack came from the left, one would be better off next time regardless of which side the attack came from.

So here’s a test for you. You may know James McNeill Whistler’s painting of his mother sitting in a chair, but can you be sure whether she is in left or right profile? Or, to take a more familiar example, the Queen’s head is shown on all of our coins. Without looking, can you say which profile she is in? Left or right?