As a child, I thought all left-handed people could mirror-write. As a left-hander myself, I occasionally tried it, starting on the right-hand side of the page and letting the letters flow leftwards. It was a nice relief from the messy scrawls I produced when writing in the standard left-to-right direction, contorting my hand to avoid smudging the ink. It also felt special: after all, Leonardo da Vinci wrote that way.

Today, I still mirror-write occasionally, and find it relaxing. But as it turns out, the skill is not a left-handed superpower after all. Instead, it's the result of a mix of fascinating factors to do with how our mind and body adapt to writing. Understanding them could give all of us a better grasp of what goes on in our brains when we write – and even make the experience more enjoyable.

The most common form of mirror-writing happens in childhood. Look at any child's first spelling books, and you'll often see individual letters and numbers written back to front, or even a whole name written backwards.

"The mirror reversals you get in childhood are a completely normal part of development. It's pretty much a stage that every child learning to write will go through," says Robert McIntosh, a professor of experimental neuropsychology at the University of Edinburgh. "It's not more common in left-handed children than in right-handed children."

There is an evolutionary reason why these reversals happen. Our brains evolved to "mirror generalise", meaning, when we look at an object, we automatically learn to recognise its mirror image as well. This is helpful because if we then see this object from a different angle, we understand that it's the same object, just facing the other way.

"The brain is set up to mirror-generalise because it's efficient," says McIntosh. "If you want to put it in an evolutionary context, imagine your mother points out a dangerous predator, a lion, and says: 'Stay away from that, that's a dangerous animal'. You want to recognise that it's the same dangerous animal when you see it walking in the other direction."

As useful as this skill is, it creates problems when we learn to read and write. Unlike a lion, letters such as "d" and "b" do change their identity depending on which way they face – but our brain evolved to just treat them as different views of the same thing. After all, if you could walk around a "d" and look at it from the other side, it would look like a "b".
Leonardo da Vinci famously 'mirror-wrote', from right to left (Credit: Alamy)
As we learn to read and write, our brain gradually figures out that mirror generalisation applies to objects in nature, but not to words and letters. Within an area of the brain known as the visual word form area, which we use to read and write, the mirror generalisation process is switched off, McIntosh says.

This process of selective suppression in the visual word form area helps to explain why, as adults, we typically can't read mirror words, but can still recognise mirror images of objects or animals.

Until children develop this ability, they are prone to reversing letters. They don't, however, do this in a random way. Instead, they are most likely to reverse letters that don't face the overall direction of the writing.

For example, in the Roman alphabet we use to write English, most letters face to the right, meaning, they have bits that stick out to the right, like tiny signposts. McIntosh compares it to flags in the wind. E, B, C and K are good examples of this. This orientation is probably the natural result of our hand and eye movements as we write, sweeping the lines in one direction. But there are some exceptions, such as J, or the number 3, which point in the opposite direction, against the wind, as it were.

This holds true for many different scripts. In the Oscan alphabet, an ancient script in Italy that was written right to left, the E, B and K look the same as in our alphabet, but are reversed – as if swivelled round, to harmonise with the direction of the writing.

Research by Jean-Paul Fischer and Anne-Marie Koch, two psychologists at the University of Lorraine in France, suggests that children implicitly grasp this rule of letters facing in the direction of the writing, then apply it to letters and numbers that don't conform to it. Other studies have shown the same pattern of children being more likely to reverse "wrong-facing" letters and numbers, such as J and 3. It's as if the children are subconsciously making the script more consistent.

McIntosh and his team found the same effect in a study using made-up, letter-like characters. The children were three times more likely to reverse a left-facing, "wrong-facing" character, than a right-facing one.

Unpublished research by McIntosh's team suggests that children writing right to left in Arabic apply that same unconscious rule, just the other way round. They are more likely to reverse Arabic letters that face right, away from the direction of the script.

Among children, accidental mirror-writing is just another developmental stage, then. But what about those of us who intentionally mirror-write, even into adulthood?

For a start, this skill turns out to be far less special than I thought. For right-handed people, and left-handed people who were forced to write with their right hand, it may simply result from the way we move as we write, according to McIntosh. When we write in English, with our right hand, we make an outward motion. If we then pick up a pen with our left hand and start to write, our natural tendency is to make that same outward movement. The resulting script flows leftwards, and the writing is reversed. "Because our left and right arms are mirror-images of one another, they naturally make mirror image movements, so the most natural way for a right-hander to write with the left hand is in mirror image," McIntosh says.

In my own case, there is a twist. I was taught to write with my left hand, using an inward motion and cramping my wrist into a kind of hook. Unsurprisingly, this feels awkward. It's more comfortable to use an outward movement, with a straight wrist – as I do when I mirror-write, which might explain why I find it relaxing. This ease only applies to writing, however, not to reading. To read my own mirror-writing, I have to hold it up to a mirror – which further supports the idea that my reversal has to do with movement, not with seeing the world differently.

It was only while researching this article that I discovered left-handers are now taught a much better way to write than with the cramped, hooked grip. It involves angling the page and writing with a straight wrist. If I had learned this style at a young age, I might not have been so drawn to mirror-writing in the first place. This discovery has given me a new writing goal: finally learning the proper left-handed technique. It may not be as cool and mysterious as mirror-writing, but it might make me feel more at peace with the ordinary, left-to-right script I use every day.

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