this post was submitted on 16 Jun 2026
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Today I Learned

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[–] village604@adultswim.fan 70 points 1 week ago (8 children)

Fun semi-related fact:

Have you ever walked outside on a bright day and it's so bright it hurts? Turns out there's a max pain limit from brightness per eye, and your brain adds them together.

By closing one eye, you cut the total possible pain in half.

[–] danekrae@lemmy.world 26 points 1 week ago (1 children)

Or just look cool and sexy by squinting.

[–] Swedneck@discuss.tchncs.de 2 points 1 week ago

migraine time

[–] NABDad@lemmy.world 19 points 1 week ago (2 children)

Absolutely unfun semi-related fact:

Sometimes when one eye is injured, the injured eye has to be removed or your body will decide the uninjured eye is bad and your immune system will destroy it.

Sympathetic Ophthalmia

If the injured eye has no chance of recovery, they scoop it out.

[–] village604@adultswim.fan 7 points 1 week ago (3 children)

Your body can also just decide it doesn't like a finger or limb and kill it.

[–] NABDad@lemmy.world 13 points 1 week ago (2 children)

Yeah, the immune system can be moronic. Intelligent design my ass.

However, there's something extra special about getting poked in one eye and having your own immune system decide that an eye for an eye means your good eye has to die.

[–] cynar@lemmy.world 4 points 1 week ago (2 children)

I think the immune system can't see the eye, so it's never trained to avoid it. If the eye is damaged, the immune system can become aware of it and start reacting. Once it starts, pulling it back is not easy.

The immune response system is simultaneously amazing and insane.

It basically deliberately scrambles part of the DNA in the immune cells that create antibodies. The rest of the body then sheds cells into the blood to move to the lymph nodes. Any immune cells that react then self destruct.

It's the equivalent of firing a paint blunderbuss at a wall, and creating a silhouette by standing in the way!

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[–] Swedneck@discuss.tchncs.de 1 points 1 week ago

that last bit is very satisfying to say

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[–] k_rol@lemmy.ca 2 points 1 week ago
[–] cevn@lemmy.world 17 points 1 week ago

This explains why I have to close one eye to go outside in the sun lol

[–] Jax@sh.itjust.works 12 points 1 week ago (1 children)

Huh, I've always closed one eye when it's super bright because it's simply more comfortable. Cool to have the behavior defined this way.

[–] AI_toothbrush@lemmy.zip 6 points 1 week ago

I never knew why the hell that worked, it seemed so bizarre and knowing it this way really is cool

[–] IPeaceInYourFace@lemmy.world 9 points 1 week ago (1 children)

Anybody else close one eye when it's too loud and they need to think?

Now it makes sense.

Less GPU usage by eyeballs, more capacity for prediction algorithms.

[–] village604@adultswim.fan 6 points 1 week ago

Same logic as turning down the radio when looking for a street.

[–] NOT_RICK@lemmy.world 5 points 1 week ago (2 children)

That is fun, I’ve wondered why that is. I also think sometimes when it’s super bright out it makes me sneeze.

[–] village604@adultswim.fan 4 points 1 week ago (2 children)

That's definitely a known thing.

My brain is weird, because if I'm super nauseous it makes me sneeze then I feel better

[–] Nurse_Robot@lemmy.world 7 points 1 week ago

Photic sneeze response

[–] sydd@lemmy.world 1 points 1 week ago

Pretty sure it's related to the vagus nerve, maybe someone more knowledgeable can chime in.

[–] Onomatopoeia@lemmy.cafe 1 points 1 week ago

Ok, John Denver! 🤪

[–] LodeMike@lemmy.today 4 points 1 week ago (1 children)

Is this that odd? We experience less pain if one of two arms has a knife in it instead of both.

[–] SpacetimeMachine@lemmy.world 7 points 1 week ago (2 children)

It is a bit odd. Your eyes feel pain to tell you whatever you are seeing might damage them if you look too long. But if you close one eye the pain can disappear entirely, even though that single eyes experience is the exact same.

[–] Rooster326@programming.dev 1 points 1 week ago

Better to go blind in one eye. Then you can have a sweet eye patch

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[–] whyNotSquirrel@sh.itjust.works 37 points 1 week ago (1 children)

I met a person long ago that had one hemisphere "dead" after several strokes. So their vision was cut in half in a way I couldn't really understand before I found out about this.

So they could just see one side (left maybe) but with both eyes, like if you took a screenshot of a FPS view and completely cut off one half of the image

[–] Whats_your_reasoning@lemmy.world 10 points 1 week ago (1 children)

I literally just finished having a migraine aura (it's only the second time I've had one, though no headache the first time and no headache yet now.) I was reading a bit about it and how it's a caused by a slow wave going across one's brain. It started in the middle of my vision on the drive home, and after I arrived it continued sweeping off to my left field of vision until it dissipated off into the periphery a few minutes ago.

It's interesting to look at this image and imagine the wave going across the back of my right brain hemisphere. It's also interesting how even the visual looked like the cone-shaped wave that follows a sonic boom, slowly spreading out.

And now, with such dire imagery and the potential for upcoming pain, I'm going to lie down and hope nothing else happens.

[–] Rachelhazideas@lemmy.world 3 points 1 week ago

Wish you a speedy post-drome. I had migraines for a year in the past, and the thought of going through that again fills me with dread.

[–] Iconoclast@feddit.uk 26 points 1 week ago (6 children)

The so-called "split brain" studies on people who have had the bridge between the two hemispheres - the corpus callosum - cut to treat grand mal seizures are fascinating. They use this method to communicate with each hemisphere separately without the other knowing.

You can, for example, give one an instruction to do something. After it has done it, you ask the other (verbal) hemisphere why they just did that, and they immediately make up a plausible-sounding explanation despite the scientists knowing it's not the actual reason.

You also get different answers for questions about dream jobs and such.

This all sparks the question: Are there two "people" in our brain the whole time or is the other created the moment the connection is cut? And which one is what I call "I"?

[–] acockworkorange@mander.xyz 9 points 1 week ago

Inside of you are two brains: a dom and a sub.

[–] nogooduser@lemmy.world 8 points 1 week ago (1 children)

You can, for example, give one an instruction to do something. After it has done it, you ask the other (verbal) hemisphere why they just did that, and they immediately make up a plausible-sounding explanation despite the scientists knowing it's not the actual reason.

Sounds like AI got something right then.

[–] Iconoclast@feddit.uk 4 points 1 week ago (1 children)

There's an uncomfortable amount of similarities between how the human brain and LLMs work.

Next word correlating with the words said before, confidently spreading false information, telling people what they want to hear.. These are by no means unique to LLMs.

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[–] enchantedgoldapple@sopuli.xyz 3 points 1 week ago

I've seen this topic covered briefly in one of CGP Grey's videos. The video also gives a POV of a person with this syndrome. The POV was surprisingly interesting to watch and I was wondering if there are other similar recorded experiments.

[–] partofthevoice@lemmy.zip 2 points 1 week ago (2 children)

2 people, that’s it? What if you are a voice machine, just voices all the way down… but you only recognize the loudest as yourself?

[–] southsamurai@sh.itjust.works 3 points 1 week ago

Fuck you very much for pointing to my brain like that ;)

[–] Swedneck@discuss.tchncs.de 1 points 1 week ago

you know what's funny? I think spongebob's brain is actually pretty damn close to how it actually works.

You've got tons of little "voices" doing quite niche tasks like recognizing faces or identifying flavours and forwarding that to another "voice" that links the flavour to memories etc etc, and a "main voice" that collates all that into coherent thought.

[–] Airfried@piefed.social 2 points 1 week ago (1 children)

You can, for example, give one an instruction to do something.

How would you do that? Since both eyes are connected to both hemispheres isn't it kind of hard to do that? Or are both ears separated and you can give commands through that without the other hemisphere knowing? I've heard about these studies too but I'm not sure about how the setup works because I've heard they used text on a screen for that but OP said the eyes do snitch to the other half after all. I find it a little confusing.

[–] Iconoclast@feddit.uk 2 points 1 week ago* (last edited 1 week ago)

By building a setup that allows the researchers to flash text on the right/left visual field. On a normal brain this information does indeed travel between the hemispheres but on a split brain it doesn't.

[–] Swedneck@discuss.tchncs.de 2 points 1 week ago (3 children)

what i want to know is whether making up an explanation is universal, or if other people would just go "no clue".
Because if EVERYONE with a severed corpus callosum just makes up explanations that is very fucking uncomfortable to think about, and i'll treasure having mine intact

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[–] Atelopus-zeteki@fedia.io 19 points 1 week ago (1 children)
[–] quick_snail@feddit.nl 4 points 1 week ago* (last edited 1 week ago) (2 children)

That seems overly complex. Can we simplify this design?

[–] captain_aggravated@sh.itjust.works 4 points 1 week ago (1 children)

Almost everything is wired in the least efficient way possible in the human brain. Everything crosses through the middle.

[–] Swedneck@discuss.tchncs.de 2 points 1 week ago

shit like this is why i'm a transhumanist, i just want a body with all the obvious inefficiencies fixed.

[–] batmaniam@lemmy.world 11 points 1 week ago

Another fun eye/brain fact: There are two "outputs" for each eye. One goes to your occipital lobe, in the back, and really processes the image ("That's a cup, it .." etc) and one goes to your brain stem, which processes movement.

It's possible to have the connection to the occipital lob severed, but not to the brain stem. It's a condition called blindsight. The result is that if you showed someone a cup, they wouldn't be "see" it; they wouldn't know what it is and wouldn't register you were showing them anything at all... but if you tossed it to them they could catch it.

[–] IPeaceInYourFace@lemmy.world 3 points 1 week ago (2 children)

That explains why one of my eyes turns off when I do loads of ket.

[–] Swedneck@discuss.tchncs.de 12 points 1 week ago (1 children)

it specifically doesn't explain that

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[–] GreenKnight23@lemmy.world 4 points 1 week ago
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