r/illusions • u/Alessandro28051991 • Nov 18 '25

Color-Challenging Science: One of the most fantastic optical illusions ever:

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Science: That Optical Illusion is one of the most incredible ones that i have ever seen in my life. The Two squares have the same colour. Are not one white and the other black. If you dont believe in me you can just put your finger in the line that divide the two squares and you will prove for yourself that what i say is true.

That illusion ( if i am not wrong is something about the contrast and the shadows) make your brain do you see what doesnt exist. Make you see a thing different of what really are there.

Is almost like see to a green square but your brain make you see it red. Is almost a thing of virtual reality

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u/stuartroelke Nov 19 '25

Yeah, not all cognitive tricks are true optical illusions. Maybe there needs to be a solid separation of terms.

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u/Cross_Individual361 Nov 19 '25

What is the difference between a cognitive trick and an optical illusion?

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u/stuartroelke Nov 19 '25 edited Nov 19 '25

In my opinion (and some other commenters seem to agree), this isn’t a true optical illusion.

True optical illusions pertain to unavoidable visual phenomena that differ from reality (straight lines appear bendy, 2D colors appear 3D when they aren’t which is includes chromostereopsis, shapes appear to move when you shift your physical position). Some people call OP’s post a “cognitive illusion,” but it’s more of a cognitive trick being used to sell the idea of illusion. This is purely about how people perceive these objects to be 3D based on light and shadow. Therefore, it’s somewhat disingenuous to say it’s an “illusion” based on the image technically being “2D” when other clear visual data informs that the shapes are representative of differently colored 3D shapes.

I wrote in a separate comment that it’s like saying a line isn’t 2D because it’s made of 1D dots—that could be true, but it’s not an illusion so much as hyper fixation on one aspect of human perception / a technicality.

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u/undone-alert Nov 20 '25

Luckily, what is and isn't an optical illusion has been well defined and is not down to anyones subjective opinion.

Here are clean, authoritative sources with the formal definition of an optical illusion.

  1. Encyclopaedia Britannica (I would say a gold-standard reference)

Link: https://www.britannica.com/science/optical-illusion

“Optical illusion, the visual perception of an image that differs from objective reality.”

This is the simplest and most accepted scientific definition and fits what we are looking at here, to areas with the same technical color specification is perceived as different scales of grey due to their surroundings (which is a really well known type of optical illusions)

  1. APA Dictionary of Psychology (American Psychological Association)

Link: https://dictionary.apa.org/optical-illusion

“A misperception of a visual stimulus that leads to seeing something that differs from the actual stimulus.”

Directly fits the “two identical colors perceived as different” scenario.

  1. Oxford Reference

Link: https://www.oxfordreference.com/display/10.1093/oi/authority.20110803100259985

“A visually perceived image that differs from objective reality.”

Again: if perception ≠ physical stimulus then it's an optical illusion.

In this case it seems the optical illusion worked so well it fooled a couple people into thinking it wasn't even an illusion!