Optical illusions that prove you can’t trust your own mind

From an article by Preston Xander

You’ve been seeing optical illusions probably since kindergarten. They’re fun little party tricks that you look at and go “Oh, that’s weird” before immediately forgetting about them. And that’s too bad, because these images are actually exposing glaring gaps in our brain’s fragile sense of reality.

For example…

Your brain changes what your eyes see to force it to make sense


This illusion is so strong that you’ll have trouble believing it even after you see it explained. Take a look at squares A and B in the above picture. The squares are the exact same shade of gray. Not the letters – the squares themselves.

Don’t believe it? Below is the same picture with the B square repeated and placed against the A square:


Now scroll back up and look at the original again. You see with your brain, not your eyes.

When you look at the world, your eyes aren’t just lenses that coldly record whatever is in front of you. Instead, your brain adjusts the image for context from moment to moment. And in this case, it’s filtering what you see based on a built-in knowledge of what shadows are.

Your brain understands that the floor is a checkerboard pattern of dark and light squares. It sees that there is an object casting a shadow over it. It knows that square B is still one of the “light” squares, even though it’s the same color in the shadow as the dark squares are in the light, so in order to avoid confusion, it automatically adjusts the lightness of square B for you before it reaches your consciousness. Keep that in mind the next time you hear some eyewitness testimony.

There are endless examples of this trickery. Take the two yellow lines in the graphic below. They are exactly the same length:


Most people see the top line as being bigger, obviously because it thinks that one is farther away due to the “tracks”. And even beyond the visual, you’re unconsciously adjusting the world for context all the time. For example, if you hold a large and small box of equal weight, you will perceive the large box as lighter. Or, if you drink soft drink after eating cake, it will taste less sweet.

What’s amazing is that you cannot un-see or un-feel these illusions despite all of the information to the contrary.

Your brain predicts the future so you can live in the present


The two red lines are actually perfectly straight and parallel, but they look like they’re bulging outward in the middle.

The blue lines are tricking your brain into believing that you’re moving toward the image, in much the same way you use lines in a doodle to show which way something is moving. Your brain interprets lines as motion.

But why are the red lines bulging? Here’s where it gets really weird – that’s the way your brain expects them to look in the future.

There’s a fair bit of calculation going on in your head from the time the light hits your eyes to the time you actually perceive something. This calculation is super quick, but it still takes time – about one-tenth of a second. That means that you’re actually living one-tenth of a second in the past at any one time.

So why are we still able to dodge fast-moving objects? Because your brain has you covered. It actually predicts the future and adjusts the world accordingly. The world you’re seeing is actually your brain’s prediction about what the world will look like one-tenth of a second after you actually perceive it. That is to say, it brings you back to the present.

Because of perspective, two parallel poles will appear to bulge out a tiny bit as you pass between them. Your brain knows this, so it automatically puts that bulge in when it thinks you’re hurtling toward the red lines. That’s right: Precognition is real, but it only allows you to see into the present.

You interpret what you see piece by piece


Here’s a picture of Barack Obama upside-down. You recognise him right away and nothing looks off about him, other than the fact that the image is flipped.

Turn him over, though, and you realise you’ve been lied to. It’s actually a terrifying alien parody of a human being.


Your brain processes visual stimuli in pieces before it makes a whole image. When you look at a face, you see a face. But what your brain sees are pieces of a face – eyes, nose, and mouth. Each piece of the puzzle is recognised separately. So even if we flip Obama, we don’t see anything weird about him as long as his eyes and mouth are the right way up.

This is due to a flaw in what’s called vestibular correction – it’s your eyesight trying to adjust for anything that’s weird about how your head is oriented (in this case, seeing it as if you were upside-down). Think of it this way: Why are movies like Cloverfield, with their shaky camera, so headache-inducing? Aren’t our eyes whipping around just as much as that camera when we’re running, or even just looking quickly around the room? Yes, but under normal circumstances, your brain steadies all of that shaky, unsteady input and gives you one smooth, coherent picture.

And your innate sense of balance tells your subconscious which way is up, so even if you tilt your head to the side, you still see a diamond as a diamond and a square as a square. Try it:


That team of graphic designers living in your head picks out every individual object in your visual field and adjusts them separately so that what you’re looking at makes sense, and it does all of this in a fraction of a fraction of a second. But it does it without a lot of attention to detail, which is why a horrible monstrosity can pose as Marylin just by standing on her head.

Sight and recognition are two separate things


This classic illusion dates back to the 1800s, and depicts an old woman and a young woman at the same time. Can’t see it? The young woman’s jawline is the old woman’s nose, and her ear is the old woman’s eye.

But here’s the key: Try to see both at the same time. You can’t. You can only switch from one to the other, no matter how hard you try.

This gets right to the heart of the matter: The act of seeing something is different from the act of recognising it. They’re two separate stages along the surprisingly complicated process of actually perceiving. So you never stop seeing the young woman – she’s always there. But you do stop recognizing her after you focus on the old hag. These two processes are so distinct that the ‘seeing’ part and the ‘recognising’ part are in two different places in your brain.

One part, the visual cortex, handles the job of rendering the image, calculating colour, motion, form, and depth. The other part handles the job of recognising what you’re seeing. So, with the image above, your visual cortex maps out the lines on the screen and then passes the paperwork to a different department, which has to then decide, “OK, so what am I looking at?” It’s brain bureaucracy.

Duck or Rabbit?
Duck or rabbit?

This can lead to some strange effects. For example, there are people out there who have suffered damage to the visual cortex and are therefore effectively blind. And yet they can still navigate obstacles, react to motion, and recognise facial expressions. They have a condition called blindsight, where their eyes work perfectly well, but they can’t form an image of what they’re looking at. Their brain is still taking in the visual information, and they’re still subconsciously recognising things like motion and expression.

Have you ever walked down a crowded street and known that a friend was coming from the other way before you actually saw him? Or sensed motion out of the corner of your eye? That’s your blindsight working to decode what’s going on around you even when you’re not paying attention to it.

You have many minds that your brain unifies


It’s almost impossible to believe, but these two tables are the same width and length. One of them has simply been turned 90 degrees. You may actually have to print this page out, cut one table top out, turn it 90 degrees, and put it on top of the other to believe it.

Or, just take a look at this one we’ve prepared earlier in Photoshop:


Your brain has over 30 different sections that deal with specific aspects of interpreting visual information, and they each have their own specialised function. Some handle shape, while others handle depth, or colour, etc.

The turned tables illusion is an example of the different parts of your mind disagreeing about what they see – is it a long thin table, or is it a fat square one? With different parts of your brain putting their own interpretation on it, it’s difficult to make up your mind.


You brain may be lying to you.