Optical illusions are some of the most fascinating visual experiences to us as humans. Whether natural or manmade, they take our biological assumptions that we use to survive every day and turn them upside down.
Take this one for example. Keep in mind, it’s a still image, nothing about it is moving… but then why do our brains interpret it as a moving image?
This illusion fools our brains into thinking there’s motion because of how our eyes move. While you may think that as you look around, your eyes move fluidly and smoothly, that couldn’t be anything further from the truth. Our eye movements are actually pretty jolty, and it’s those small usually unnoticeable jolts along with the lag in our brain’s visual processing that makes this image appear to move. If you focus steadily on the center of one circle, you’ll notice that the image stops moving. This hypothesis was confirmed by a 2012 study from St. Joseph’s Hospital in Phoenix, Arizona.
Not every illusion works the same way, but nearly every one reverse engineers our biological presets. Take a look at this one… Which square, A or B, do you think is darker?
The boxes are the same color. Researchers at MIT investigated this illusion and found the reason it works to be twofold. First, our brains are trained to recognize patterns and due to the checkerboard, we think that the squares should naturally alternate colors. Secondly, our brains inherently understand shadows, but in the case of images, shadows darken the color image behind it. With these two visual predispositions programmed into our brain, we are fooled into interpreting the image like we would any 3D object, but in actuality, the squares are the same color.
Optical illusions as a whole draw on a few biological problems that we have too. Our visual processing only updates about every 1/1oth of a second. This is incredibly slow, so our brains have developed methods of stitching our visual senses together to create flowing images. Our brains do this so we can keep ourselves from getting hurt or kill prey for food, but visual illusions exploit this time deficiency.
Diverging from physical problems, our brain has also trained itself to recognize patterns, estimate light, and essentially to fill in the gaps to what our eyes miss. All of these skills work to our benefit in normal life, but illusions take these biological predispositions and reverse engineer them to trip our brains up – to our enjoyment of course.
Take this, it’s called the Ebbinghaus illusion. Those orange circles, they’re the same size.
Our brains do this because they have developed to estimate relative size based on references around an object. This helps us recognize scale at great distances, but when thrown into a 2D image, our brain gets confused.
Now look at this circle of pink dots and stare at the cross at the center. You’ll find that after a few seconds, it starts to appear that as a pink dot is removed, a green one is put in its place.
This all has to do with something called Troxler’s effect. As the dots moves in our peripherals, they become blurred and our brain isn’t focused on processing things outside of our focus as fast. Along with this, as the dot disappears, since our brain is used to seeing the purple dot, when it is gone, it fills it in with purple’s complementing color, green. In essence, green is the exact opposite of purple, so when the purple dot disappears, our brains fill it in with what it thinks should be there, as explained by Nature magazine.
Why does this elephant look to have a ton of legs? Because our brains don’t understand how to interpret the impossible lines in reference to our idea of what an elephant should look like.
Why does this image look like there are black dots where each lines cross? Because our brain makes assumptions about contrast and patterns when not in focus to help us stay safe.
Why do these center lines look like different sizes? Because the reference lines our brains use as scale distort its ability to measure the size of the center line.
Every optical illusion exploits our brains naturally evolved capabilities at recognizing patterns, filling in visual gaps, and otherwise helping us stay at the top of the food chain. While illusions may be fun to toy with, they actually help biologists and psychologists understand our brain to a deeper level than ever would be possible.
So, next time you see an optical illusion, think of it as much much more than just a fun image, it’s a highly scientific trick designed to reverse engineer your biological assumptions…