this post was submitted on 19 Aug 2025
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Science Memes

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[–] diverging@piefed.social 83 points 2 days ago* (last edited 2 days ago) (7 children)

Because of this we have blind spots, one for each eye. They are not usually noticeable because 1) the blind spot of one eye can usually be seen by the other, and 2) the brain fills in the gap.

So with this I will perform a magic trick, I will make your thumb disappear: Close your left eye and with your right look at a spot in the background, make a thumbs up gesture and place the tip of your thumb on that spot, move your thumb to the the right continuing to look at the spot in the background, when your thumb moves about 15 cm your thumb should disappear.

You can use your left eye too, just switch the directions.

[–] InvalidName2@lemmy.zip 43 points 2 days ago (2 children)

It's way too late at night for all those directions, somehow ended up creating my own blind spot by sticking my thumb in my bum.

[–] diverging@piefed.social 18 points 2 days ago

Well, I guess your thumb disappeared.

I can try another way the blind spot is about 15 cm at arms length to the right of the right eyes center of vision. So put your thumb there and it should disappear

[–] tacosanonymous@mander.xyz 5 points 2 days ago

At least your dick didn’t get stuck in the toaster.

[–] Carrot@lemmy.today 7 points 2 days ago (1 children)

Woah, i didn't know that the effect would be so drastic. I want to point out to those struggling to get it to work that, as diverging mentioned, your arm needs to be fully extended. Also, the blind spot is about a thumb's width, at least for me, and is only visible at a specific x/y axis location. Any deviation from that single spot will cause it to stop working. I could tell I was close to the spot when parts of my thumb would disappear, and just had to slowly move it around until I found the spot that looked like the thumb was gone completely.

[–] 0ops@piefed.zip 3 points 2 days ago

Thanks you helped me see it (or not see it I guess)

[–] drmoose@lemmy.world 25 points 2 days ago* (last edited 2 days ago) (2 children)

the brain fills in the gap

To expand on this, current leading theory (predictive processing) says that brain first generates a visual image then confirms it with inputs and if there's no input to confirm/deny the halucination it's just accepted as is. So we can have a whole load of blind spots in all of our sensors and continue functioning rather well with an ocassional artifact.

I think about this at night when my eyes are forced to attempt to make sense of the low light levels in a dark room. I know my room isn't grainy and grey-scale - that's just the best my eyes and brain can do at night. It's interesting to look around and try to imagine the proper colors and shapes of things, reckoning the difference between what I know and what I see in the moment.

With our brains constantly making things up to explain gaps in information, it's no wonder kids think they see "monsters" in the dark. It's also no wonder that nightlights work well to keep said "monsters" away.

[–] BuboScandiacus@mander.xyz 3 points 2 days ago

AI witchhunting crowd hates this one simple trick !

[–] callyral@pawb.social 5 points 2 days ago

It looks like there's just a gap in spacetime or something.

By the way, your eyes are not meant to track your thumb when doing this, you have to keep still and move only your thumb for it to work, so don't move your eyes.

[–] Eq0@literature.cafe 3 points 2 days ago

Succeeded, thanks! That’s uncanny!

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

I couldn't make it work. But I did notice that the spot in the background changed focus a tiny bit at one point. I suspect my brain was tracking the thumb and simply refused to continue to truely focus on the background spot. I tried and tried, but just couldn't make it happen. Neither eye. :(

[–] Catoblepas@piefed.blahaj.zone 2 points 2 days ago

Make sure to hold it at arm’s length, if you weren’t already. If it’s close to you it’s too big to vanish into the blind spot.

[–] clot27@lemmy.zip 3 points 2 days ago (1 children)

What is a "spot in the background"? Like where exactly

[–] Todd_cross@lemmy.dbzer0.com 11 points 2 days ago* (last edited 2 days ago)

Anywhere. It makes it easier, if you have a dot or a feature to look at, but really it's anywhere in the distance. I guess generally straight ahead.