When British neurosurgeon Henry March sat at his patient’s bedside after surgery, he knew the bad news he was about to deliver was his fault.
The man had a pinched nerve in his arm that required surgery, but after making a midline incision in his neck, Marsh punctured the nerve on the wrong side of his spine.
Preventable medical errors often involve surgery on the wrong side, for example, an injection in the wrong eye or a biopsy from the wrong breast.
These “never events” (medical terms for serious and largely preventable patient safety incidents, that is, not supposed to happen) highlight that while most of us have been taught left and right When we were kids, not all of us did so well.
While distinguishing between left and right is as easy for some people as distinguishing between up and down, a significant minority (about one in six people, according to a recent study) struggle with this distinction. Even for those who think they’re not having a hard time, distractions like ambient noise or having to answer questions that aren’t related to what they’re doing can get in the way of getting the right answer.
“Nobody has a problem saying (that something is) from one side to the other, or from top to bottom,” says Ineke van der Ham, an assistant professor of neuropsychology at Leiden University in the Netherlands.
But the differentiation between left and right is different. “It’s because of the symmetry and because when you turn around it’s the other way around, and that makes it very confusing.”
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Distinguishing between left and right is actually a complex process that requires memory, language, visual and spatial processing, and mental rotation.
In fact, researchers are beginning to understand exactly what happens in our brains when we do this, and why it’s so much easier for some people than others.
“Some people can instinctively distinguish between right and left. They can do it without thinking,” says Gerard Gormley, a physician and professor at Queen’s University Belfast in Northern Ireland. “But others have to go through a process.”
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In an effort to understand what happens in medical errors involving the wrong side, Gormley and his colleagues investigated the experience of medical students making left-right decisions and examined the process.
“First, you have to orient yourself from right to left,” he says.
When the answer doesn’t come immediately, the participants describe different techniques, from making an L with their thumb and forefinger, to thinking about which hand they use to write or play the guitar. “For some people, the reference might be a tattoo or body piercing,” says Gormley.
So when you figure out which side the other person is standing on, left or right, the next step is for you to mentally look in the same direction as the other person. “If I were facing you, my left hand would be facing your right hand,” says Gormley.
“The idea of mentally rotating an object adds an extra layer of complexity.”
Other research shows that people find it easier to judge whether an image shows their left or right hand by imagining their own hand or body.
Research published by van der Ham and his colleagues in 2020 revealed that about 15% of people consider themselves inadequate when it comes to determining right and left.
Nearly half of the 400 study participants said they used a hand-related strategy to determine which was which.
The researchers used the so-called Bergen test to distinguish between left and right to gain insight into how these strategies work.
Participants looked at images of people drawn as stick figures. Some figures were looking at them and some were not, and they held their arms in different positions. People then had to identify which hand stood out, whether it was left or right.
“It sounds simple, but it’s a bit frustrating if you have to do it a hundred times as fast as you can,” says van der Ham.
In the first experiment, the participants sat with their hands on a table in front of them.
“There was a very clear influence on the way this little doll was positioned,” says van der Ham. If you look at the back of the head, it lines up with you, so people were much faster and more accurate. “
Similarly, when the wrist was facing the participant but with the hands crossed so that the left hand was on the same side as the participant’s left hand, people tended to do better.
“It tells us that the body is really involved in this,”
The next question was whether the participants were using signals from their bodies at the time of the test to determine left and right, or whether they were using a stored idea about their body as a reference.
To answer this, the researchers repeated the experiment, but this time they tested four different scenarios: the participants sat with their hands crossed or uncrossed on the table in front of them and their hands were either visible during the test or covered with a black cloth.
But the researchers found that none of these changes affected the performance of the test. In other words, the participants did not need to see their hands to use their bodies to distinguish between right and left.
“We haven’t completely solved the problem,” van der Ham says. “But we were able to identify our bodies as a key component of the left-right distinction, and we wondered about representing our bodies in a more consistent way.”
In Van der Ham’s experiments, the increase in performance resulting from adapting to the wrist was most pronounced in subjects who said they used a hand-linked strategy to distinguish between left and right in their daily lives, as well as in women in general.
The researchers also found that men tend to respond faster than women, but the data doesn’t support previous studies that have shown that men do better overall on tests of left-right discrimination.
It’s not clear exactly why people differ in their ability to distinguish between left and right, although research suggests that the more asymmetrical a person’s body (in terms of preference for handwriting, for example), the easier is to distinguish between right and left.
“If one side of your brain is slightly larger than the other, you tend to have better differentiation between left and right,” Gormely says.
It could also be something we learn in childhood, says van der Ham, like other aspects of spatial cognition.
“If kids are responsible for leading the way, if you allow them to walk a few feet ahead of you and make decisions, those are the kids who end up being better navigators,” she says.
Research by Alice Gomez and her colleagues at the Lyon Neuroscience Research Center in France suggests that distinguishing between left and right is something that children can quickly learn.
Gomez designed a two-week teacher-led intervention program to increase body representation and motor skills for children ages 5-7.
When the ability to locate the correct body part on oneself or a partner (the right knee, for example) was tested after the program, the number of left-right differentiation errors was nearly halved.
“It was very easy for us to increase the children’s abilities to locate [the body part] by name,” Gomez says.
One of the reasons for this may be that the children learned a strategy: think about which hand they use to write when they don’t remember the right and the left.
The show’s focus on children’s bodies is another possible explanation, especially since other research shows that an egocentric frame of reference is key when making left-right decisions.
In a regular classroom, children may name the doll’s body parts instead of their own, because the latter is more time consuming and more difficult for the teacher to assess, Gomez says.
While there are many everyday scenarios where it’s important to distinguish between left and right, there are some situations where this is absolutely vital.
Neurosurgeon Marsh successfully corrected nerve decompression surgery, but a situation in which a surgeon removed the wrong kidney or amputated the wrong limb, for example, would have dire consequences.
Medicine isn’t the only field where left-right mistakes can mean the difference between life and death: the boatswain may have steered the ship to the right instead of the left in the sinking of the Titanic.
But while some people have to work harder to distinguish between left and right, everyone is likely to make these wrong decisions, Gormley says.
The expert hopes that increased awareness of the ease of making such mistakes will reduce the stigma for those who need validation of their decision.
“As health professionals, we spend a lot of time marking spatial orientations (near, far, up, down), but we don’t pay attention to left or right,” he says. “And indeed, of all the spatial orientations, this is the most challenging.”
About one in ten people is left-handed, and twin studies have shown that genes play a role.
A study from the University of Oxford in the UK recently revealed four regions in human DNA that appear to play an important role in determining whether someone is left-handed or right-handed.
Those who were left-handed had “mutations” in four genes that code for the body’s cytoskeleton, the complex scaffolding found inside cells to help organize them.
Scans of people with these mutations showed that the white matter in their brains had a different structure.