this post was submitted on 16 Jun 2026
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Today I Learned

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[–] batmaniam@lemmy.world 12 points 1 day 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.

[–] village604@adultswim.fan 92 points 2 days ago (11 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.

[–] IPeaceInYourFace@lemmy.world 10 points 1 day 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 7 points 1 day ago

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

[–] NABDad@lemmy.world 24 points 2 days 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 2 days ago (3 children)

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

[–] NABDad@lemmy.world 18 points 2 days 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 day ago (1 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!

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

My immune system pisses me off constantly.

It let COVID through three times despite me rigorously keeping up to date with the vaccines as much as possible, and at the same time it has destroyed my thyroid gland and it has declared cherries and peaches as terrorist infiltrators.

I feel like if my immune system is so bored it needs to attack harmless things, I should never have to deal with any actually harmful thing.

It's like a cop that beats up an unarmed teenager, but hides when someone is shooting up a school.

[–] cynar@lemmy.world 2 points 1 day ago

I definitely think there are grounds to the cleanliness hypothesis. Basically the immune system expects a certain amount of activity. If it's underperforming, the body systems assume it's a problem with the immune system, not a lack of bugs, because we are too clean. It then racks up activity levels, causing problematic autoimmune or allergy reactions.

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

that last bit is very satisfying to say

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[–] k_rol@lemmy.ca 3 points 2 days ago
[–] Jax@sh.itjust.works 20 points 2 days 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 day ago

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

[–] danekrae@lemmy.world 30 points 2 days ago (1 children)

Or just look cool and sexy by squinting.

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

migraine time

[–] cevn@lemmy.world 21 points 2 days ago

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

[–] NOT_RICK@lemmy.world 6 points 2 days ago (4 children)

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

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[–] Airfried@piefed.social 3 points 2 days ago

I did notice that but I never even wondered why that is. Neat!

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[–] whyNotSquirrel@sh.itjust.works 47 points 2 days 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 13 points 2 days ago (2 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.

[–] LetThereBeNick@lemmy.zip 2 points 1 day ago

It is really cool to perceive some of the structure of your visual cortex in cases like this. Another example is watching the patterns when your eyes are closed for a while in a dark room. Those spreading waves you can sometimes see resemble the activity recorded from cortex at rest.

[–] Rachelhazideas@lemmy.world 3 points 1 day 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 34 points 2 days ago (9 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"?

[–] Swedneck@discuss.tchncs.de 3 points 1 day ago (1 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

[–] Iconoclast@feddit.uk 2 points 1 day ago (1 children)

I'm no neuroscientist but I don't think this has anything to do with the two hemispheres being separated - it's just how the human mind works. When something happens we come up with an explanation for it that's sometimes factual and sometimes completely made up. These people don't know that they're making it up - they genuinely believe the reason they're giving. We're not comfortable with uncertainty, especially when it comes to our own behavior.

I'm personally one of the people who doesn't believe in free will so these findings make perfect sense to me and are in no way in conflict with my worldview, but I get how hearing about this might make someone else uncomfortable.

[–] Swedneck@discuss.tchncs.de 1 points 15 hours ago

What's your source (and i don't mean a citation, more like reasoning) for us making things up even without brain damage? That, uh; feels made up, ironically.

Like i'm not saying i sit around contemplating every single assumption i make, but i can't recall ever realizing my explanation for something was just completely not based in reality. If i'm not sure then i just say i'm not sure, it's something i've specifically made an effort to be precise about (for example i've rewritten a bunch of this text several times as i decide what parts i know and what parts i recon).

The idea of uncontrollably coming up with incorrect explanations is uncomfortable to me not because of uncertainty, but because it would make me fundamentally unable to approach closer and closer to """objective""" reality.
I like uncertainty because it means i'm not mistakenly stating something as fact, and thus deluding myself (and potentially others). I kind of prefer to say "i'm not sure" because it means i'm not risking accidentally hiding the truth, it can always be improved upon later.

[–] acockworkorange@mander.xyz 10 points 2 days ago

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

[–] nogooduser@lemmy.world 9 points 2 days 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 5 points 1 day 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.

[–] Swedneck@discuss.tchncs.de 1 points 15 hours ago* (last edited 15 hours ago)

that's so interesting, really makes you purple apple rubber ducky table tennis on tuesday?

[–] enchantedgoldapple@sopuli.xyz 3 points 2 days 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.

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[–] Atelopus-zeteki@fedia.io 23 points 2 days ago (1 children)
[–] quick_snail@feddit.nl 5 points 2 days ago* (last edited 1 day ago) (2 children)

That seems overly complex. Can we simplify this design?

[–] captain_aggravated@sh.itjust.works 5 points 1 day 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 15 hours ago

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

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

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

[–] Swedneck@discuss.tchncs.de 16 points 1 day ago (1 children)

it specifically doesn't explain that

[–] IPeaceInYourFace@lemmy.world 2 points 18 hours ago

That explains why I can't read when I've sniffed ket

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