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An Optical Illusion




As a person who has an interest in the nature of perception, and also as an artist, I have been long fascinated by optical illusions. I've seen a lot of them, but this one caught my attention today as I was looking up 'darkness' as a wiki entry:


Square A is the same shade as square B.

It seems unbelievable, but it's true.

I'm pretty familiar with the concept of relative shading but I thought I would do a little experiment. Despite the impression of different values in my mind from seeing this picture, I was fully confident that the author was correct (having seen a similar illustration before) and they were the same shade. However, just for fun, I copied the pic and pasted it in my photoshop program. Then I took the eyedropper tool and sampled both squares. Lo and behold, all Red Green and Blue attributes were 120 for both squares, an exact match.

Then to see how it would look, I took the paintbrush with the sampled color selected and did this:


It is interesting that the effect of gradation is a complete illusion. It looks like a smooth blend, doesn't it?

In fact, if you relax your focus and stare somewhere in the middle of the two squares you might see the two blocs and their connecting line as a whole pop out of the background.


The nature of perception sure is neat.

What's even more interesting is how the lesson of this simple visual trick can be used to extrapolate other facts in the areas of life. There are certain redundancies or patterns in existence, and what is observed in the visual realm can be also observed in other realms. Not only in our external senses, light, sound, (energy), ect., but within our minds as well, especially since all of our senses are filtered through interpretative mechanisms that apply subjective meaning and causality to the things we experience. In short, how the mind perceives the stimuli and puts together a mental representation of it, (as viewing is an active process, not a passive one), those same mechanisms may also be similar to how we consider abstract concepts.

So, despite how it looks, the two squares are the same but only appear different simply by the contrasting values around them.

Makes you wonder, then, what other things in life are actually the same but which their sameness is obscured by the particular framing, intentional or otherwise, of the environments around them?



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I've seen it before, but it's still amazing. Having joined the squares up the impression that that joining line has a gradient fill on it is huge.

Interestingly, and if you can do stereograms ('Magic Eye' 3D thingies) you can try this, if I overlay the image from the two eyes so that A is right next to B, they still don't look similar. The brain must cut in very early with the context.

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That is a cool illusion. Your assumptions are pretty spot on as well. Our brains are in the business of making sense of the world around us, often at the expense of reality. Survival would be difficult, and/or overwhelming at times if we were to perceive an often confusing reality in its raw form. Our brains will automatically and without our permission, give us a distorted interpretation of reality. This illusion is a classic example of the brain filling in and even changing some of the blanks in order to offer a coherent perception, given the surrounding pattern.

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Mind is blown, talking about more than meets the eyes. I've seen it before but your analysis was very very good and helped me to understand this thing better. Very good entry Kzop, thank you very much for it.

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Fizzydog: Right! That's what I said, too.

Bob: I love stereograms, those things still amaze me. How do they do it?!

Schmoo: You actually preempted my next post which will be the examination of the blind spot we all have and how the mind fills in the blank spot by using the surrounding elements, or, the context. I wanted to make a parallel between that and how we make other, more abstract, judgments.

The AUT: Thanks man! If you found that interesting, you might want to take a look at the phenomenon called "change blindness". This lab has done some really good (and funny work):


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Try squinting.

It worked :P

Anyway, this was pretty cool, Oti. Thanks for posting it :) My perceptual studies are limited to that of the sonic/aural nature, so it's kinda neat to listen to someone who knows something about the other kinds, y'know?

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