 |
| Why are some people unable to distinguish between right and left? |
When British brain surgeon Henry Marsh sat by his patient's bedside after surgery, the bad news he was about to deliver was his own fault. The man had a pinched nerve in his arm that required an operation.
But after making an incision in the middle of his neck, Henry Marsh pulled out the nerve from the wrong side of his spinal column.
Mistakes that can be prevented include operating on the wrong side of the site, for example injecting into the wrong eye or doing the wrong breast biopsy. Errors that should not occur can be very serious in terms of patient safety and are largely preventable.
These mistakes point to the period when most of us learn how to distinguish left from right in the childhood. Not everyone can identify it correctly.
While it is as easy for some people to tell the difference between right and left as it is to tell the difference between bottom and top, there is a substantial minority of us who cannot. According to a recent review, one in six have difficulty distinguishing right from left. Even people who think they have no difficulty making the distinction have difficulty making the right choice due to distraction, environmental noise, or answering irrelevant questions.
What changes in the brain of left-handed people?
About one in 10 people are left-handed, and studies of twins have shown that genetics play a role. A recent study at the University of Oxford identified four parts of human DNA that play a role in determining whether a person is left-handed or right-handed.
Left-handed people were found to have 'mutations' in four genes that code for the body's cytoskeleton, the complex system found between cells that help organize them. Scans of people with this mutation showed that their brains had a different structure of white matter. Left-handed people were also better connected to the left and right sides of the brain than right-handed people.
'Some people are born with the distinction between right and left without thinking,' says Gerard Gormley, a GP and clinical professor at Queen's University Belfast in Northern Ireland. 'But others have to go through a process. Is.'
To understand why errors occur in medical cases, Professor Jared Gormley and his colleagues investigated the ability of medical students to identify left and right and examined the process.
"First you have to identify the difference between right and left yourself," says Professor Gromley. From thinking about which hand they use to write, or which hand they play the guitar with to describe different ways.
Professor Gormley says, "For some people, this decision is based on their body markings, such as tattoos."
Then when it comes to figuring out which part of the person standing in front of you is right and which part is left, the next step is to mentally rotate yourself so that you are in the place of the other person standing in front of you.
"If I'm in front of you, my left hand will be in front of your right hand," says Professor Gromley. "This idea of mentally rotating something adds complexity."
Other research in this regard shows that people rotate their hands or bodies in their minds and thus find it easier to decide which is the left or right hand in a mental image.
A 2020 study published by van der Ham and colleagues found that when it comes to left-right identity, about 15 percent of people feel they are incompetent to make that decision.
About half of the 400 participants in the study said they used hand-related strategies to determine whether they were right-handed or left-handed.
The researchers used a test called Bergen-Right-Left that discriminates how different strategies work. Participants viewed images in which stick figures were either looking towards them or away from them and with their arms in various positions, and had to identify the highlighted hand as their left or right. was
'It sounds easy,' says van der Ham, 'but if you have to quickly identify a hundred of them, it's annoying.' In the first experiment, participants sat with their hands on a table in front of them. "There was a very clear effect of how the stick people were sitting," Van der Ham says. "If you were looking at the back of the head, it was the same way you were sitting, so people were very sharp." And more even were answering. Similarly, says van der Ham, when the stick figures were in front of you and their hands were on top of each other, with their left hand in front of the participant's right hand, the proportion of people who answered correctly Was better. This tells us that the body is really fully involved.
The next question was whether the participants were using their body gestures to identify left and right at the time of the test or whether they were using the diagram in their minds. To answer this, the researchers repeated their experiment, but this time in four different ways: participants sat with their hands either crossed or crossed on a table in front of them, and during the test, their hands or So were visible or covered with black color. But the researchers found that none of these changes affected test performance. In other words, participants did not actually need to see their hands to use their bodies to distinguish right and left.
"We haven't completely solved the problem," Van der Ham says. But we were able to identify our body as a key factor in identifying right from left, and we consult our body.
In van der Ham's experiments, when people's positions corresponded to those made of sticks, the increase in performance was more pronounced for those who said they used their hands to tell left-right in their daily lives. , it was also commonly found in women.
The researchers also found that men were faster to respond than women, but the data did not support previous research showing that men performed better overall on left-right discrimination tests. Perform.
It's not entirely clear why people differ in their ability to distinguish between left and right, but research suggests that the more asymmetric one's body (especially which hand is used for writing) In this context), it seems easier to differentiate them into left and right. "If one part of your brain is a little bigger than the other, it's easier for you to distinguish between right and left," says Gormley.
But it could also be something we learn in childhood, such as awareness of surroundings, says van der Ham. "If children are given the responsibility of finding their way and you let them make decisions about walking just a few meters ahead of you, they become better navigators," he says.
Research by Alice Gomes and colleagues at the Lyon Neuroscience Research Center in France suggests that distinguishing between left and right is something that children can learn quickly. Gomez designed a two-week program that was run by teachers. It was designed to develop body part recognition and motor skills in five- to seven-year-old children.
When they were tested on their ability to locate the correct body part of themselves or a partner, for example, their right knee, after the program, the number of errors in differentiating between left and right almost halved. left
"It was very easy for us to develop children's ability to identify body parts by name," says Gomez.
One reason for this may be that children were taught a strategy to think of the hand they write with if they forget the difference between right and left. Focusing on children's own bodies in the program potentially demonstrates, as research also suggests, that self-reference is key when we judge left and right.
Although the right-left distinction is important in many everyday situations, there are occasions when the distinction is critical.
Brain surgeon Marsh was able to correct wrong-side neurosurgery, but if a surgeon removes the wrong kidney or amputates the wrong organ, the consequences can be disastrous.
Medicine is not the only field where mistakes can make the difference between life and death. It is possible that turning the ship to the right instead of the left was a major factor in the sinking of the famous ocean liner Titanic.
Gormley says that while some people have to make more effort to decide between left and right, everyone can misjudge left and right. They hope that more awareness of how easy it is to make such a mistake will lead to less embarrassment for those who need to reaffirm their decision.
He adds that as health professionals, we spend a lot of time making judgments about surroundings, near and far angles, etc., but don't pay attention to the distinction between right and left. But actually, the difference is you, this is the most difficult of abilities.