Why some people can't tell left from right

Authored by bbc.com and submitted by Sariel007

When British brain surgeon Henry Marsh sat down beside his patient's bed following surgery, the bad news he was about to deliver stemmed from his own mistake. The man had a trapped nerve in his arm that required an operation – but after making a midline incision in his neck, Marsh had drilled out the nerve on the wrong side of his spinal column.

Preventable medical mistakes frequently involve wrong-sided surgery: an injection to the wrong eye, for example, or a biopsy from the wrong breast. These "never events" – serious and largely preventable patient safety accidents – highlight that, while most of us learn as children how to tell left from right, not everyone gets it right.

While for some people, telling left from right is as easy as telling up from down, a significant minority – around one in six people, according to a recent study – struggle with the distinction. Even for those who believe they have no issues, distractions such as ambient noise, or having to answer unrelated questions, can get in the way of making the right choice.

"Nobody has difficulty in saying [something is] front and back, or top and bottom," says Ineke van der Ham, professor of neuropsychology at Leiden University in the Netherlands. But telling left from right is different, she says. "It's because of the symmetry, and because when you turn around, it's the other way around, and that makes it so confusing."

Left-right discrimination is actually quite a complex process, calling upon memory, language, visual and spatial processing, and mental rotation. In fact, researchers are only just beginning to get to the bottom of exactly what's going on in our brains when we do it – and why it's much easier for some people than others.

StrangersWithAndi on January 16th, 2023 at 18:29 UTC »

As a kid / teen, I would look at my hands with my thumbs out to see "which one made an L" so I knew which was left.

My dad used to make fun of me by holding out both hands and crying, "Neither hand makes an R!"

Drop me anywhere in the world, though, and I can point you unerringly to the north.

Loisalene on January 16th, 2023 at 17:00 UTC »

When I was learning how to write, it was drummed into our heads that "right is the hand you write with".

I am left handed.

wubwub on January 16th, 2023 at 15:20 UTC »

I am pretty good at spacial orientation and navigation and can usually point north (or at least north-ish) wherever I am, but if you ask me to point "left" or "right" I often have to stop and even look at my left hand before I can give an answer.

I used to laugh at the idea of surgeons using a sharpie to mark which side to operate on, but then I thought about how bad I am at telling left from right.

As a surgeon, if they told me to operate on the body part on the north side, I'd probably be fine. Just not if they said "operate on the left knee".