Have you ever wondered how you can see a cube that isn’t really there or why a window seems to spin in different directions? These are examples of optical illusions, which are more than just tricks—they help us understand how our brains make sense of the world. In this article, we’ll explore some fascinating optical illusions and discover how they work. By the end, you’ll have a better idea of how you know that what you see is real.
Every moment you’re awake, your brain is doing something amazing. It’s taking signals from your eyes and creating a 3D world for you to experience. This process is called spatial perception. It’s how you understand the space around you, helping you move around and avoid obstacles.
Our world has three dimensions: up-down, left-right, and near-far. But your eyes only see a 2D picture. So, how does your brain figure out how far away things are? It uses clues hidden in the 2D image.
Imagine two circles that look the same size. How do you know which one is closer? Your brain uses clues like size and focus. When something is closer, it takes up more space on your retina. If you don’t have enough clues, your brain might think the bigger circle is closer, even if they’re the same distance away.
More clues help your brain build a better picture of reality. For example, if something is out of focus or partly hidden, it might be farther away. When you draw, you might notice that objects on the ground line look flat. But if you add a horizon and use size and overlap, you can create a 3D effect.
Take a look at a picture with a path leading to the horizon. The path’s parallel lines seem to meet at a point called the vanishing point. This is called linear perspective, a technique that artists in Europe discovered in the 15th century. It helps create depth in art and is one of the clues your brain uses to understand distance.
One of the most mind-bending illusions is the Ames window. It looks like it’s spinning back and forth, but it’s actually just rotating. This illusion works because of how your brain interprets shapes and angles. Even people from different environments see the illusion the same way, showing that our brains are wired to see reality in a certain way.
Another cool illusion is the Ames room, where objects seem to grow and shrink. The room’s walls and floor are skewed, tricking your brain into seeing a false reality. This kind of illusion is called anamorphism, and artists have used it for centuries. A famous example is Hans Holbein’s painting “The Ambassadors,” where a gray shape turns into a skull when viewed from a low angle.
Have you ever seen a chair that isn’t really there? The Ames chair illusion uses strings arranged in a way that your brain interprets as a chair. This happens because your brain looks for patterns and connectivity. When lines come together to form corners, your brain assumes they’re connected, creating the illusion of a chair.
When you look at the night sky, you might see shapes formed by stars, known as constellations. Different cultures see different shapes, but some, like Orion, are recognized worldwide. This shows how our brains connect dots to create familiar patterns.
Many of these illusions were created by Adelbert Ames, who started as a law student but switched to art. He wanted to make realistic art by understanding how the eye sees the world. His illusions reveal how our brains interpret visual information.
To understand size and distance, your brain uses binocular vision. Try holding two pencils in front of you. When you focus on the back one, the front one appears doubled. This happens because each eye sees a slightly different image, and your brain combines them to judge distance. Other clues like texture and parallax also help you understand what you see.
Our brains use bits and pieces of information to build a picture of reality. Most of the time, this works well, but illusions show us that sometimes, incomplete information can trick us. Despite this, people from different backgrounds often see the world in similar ways, thanks to evolution. Isn’t it amazing how our brains work?
Stay curious and keep exploring the wonders of perception!
Design an optical illusion using paper and colored pencils. Try creating a drawing that uses linear perspective to make a flat image appear 3D. Share your creation with the class and explain how your illusion tricks the brain into seeing depth.
Watch a video about the Ames room illusion. Discuss with your classmates how the skewed walls and floor create the illusion of changing sizes. Then, in groups, brainstorm ideas for creating a mini Ames room model using cardboard and other materials.
Look at images of different constellations and try to identify the shapes they form. Then, use a star map to create your own constellation by connecting stars in a unique pattern. Present your constellation to the class and describe the story behind it.
Conduct an experiment to understand binocular vision. Hold two pencils at different distances and observe how they appear when focusing on one. Discuss with your classmates how this experiment demonstrates depth perception and how your brain combines images from both eyes.
Research anamorphic art and find examples online. Choose one piece and try to recreate it using chalk on the sidewalk or paper. Share your artwork with the class and explain how anamorphism tricks the brain into seeing a 3D image from a specific angle.
Thank you to Policygenius for supporting PBS. How can you see a cube that isn’t really there? Why does this window spin one way and then the other? How can something shrink before your eyes and then grow again? And why do you see a chair where there is none? Optical illusions like these are more than just tricks. They can actually help us unlock the secrets of how we make sense of the world around us, and even how we construct reality itself. In this video, we’re going to explore a variety of mind-bending optical illusions and dig deep into how they work, to try and answer one important question: How do you know that what you see is real?
Hey smart people, Joe here. Every waking minute of every day, your brain is doing something truly incredible. It’s taking countless tiny electrical impulses from your eyes and creating a fully functional three-dimensional reality. The scientific term for this is spatial perception, and it’s one of the most fundamental ways that you make sense of the world around you. If you want to move around your environment, you need to be able to detect obstacles and know how they are arranged.
Space has three dimensions. When it comes to how your eye sees the world, those three dimensions are not created equal. Your brain has to make sense of a 3D world using a 2D picture. You can put objects in order in the up-down dimension by how those images land on your retina, and the same with left to right. But how do you figure out how far away an object is? Even though all the light coming into your eye hits the back as a flat image, hidden in that 2-dimensional picture are clues.
These circles are the same size, but how far away is each circle? Looking from here, you can clearly see which one’s closer. The illusion worked; you couldn’t figure out size and distance because you didn’t have enough clues. When you look through here, the only information your eye has is which circle is bigger. When things are closer, they literally take up more area on the back of your eye than when they’re far away. So with no other clues present, your brain thinks the bigger thing is close, and the smaller thing is far, even though they’re the same distance away.
Of course, if you have more clues, you can get a better picture of reality. One clue is that something may be slightly out of focus, and you also can’t see all of these things. If you can’t see all of something, then it’s farther away than the thing that you can see all of. You need more clues!
Another clue explains why the drawings you did in kindergarten look so awful. The first thing you do is draw the ground, right? Then maybe you put a tree over here, a house, and a person. But how do you tell what’s closer and what’s farther away when they’re all standing flat on this line? You can’t! If you can see the ground and the horizon, you can tell how far away things are. When you add in other clues, like how big things are and what’s on top of what, you can start to build a three-dimensional reality.
Take a picture like this. It’s full of clues! These trees closer to the horizon are higher up in the picture, so they’re farther away. The most important clue in this image is linear perspective. Even though a path like this is made of two parallel lines, they appear to meet at a point on the horizon called the vanishing point. Noticing this linear perspective is one of the big things people in Europe figured out around the beginning of the 15th century, which is why art evolved significantly during that time.
These are just a few of the clues you use every day to build your reality, and you don’t even have to consciously think about them! That’s incredible! Give yourself a pat on the back.
Now, let’s talk about one of the all-time great mind-breaking illusions: the Ames window. The window appears to be turning normally until it stops and spins the other way. Most people see this window oscillating back and forth infinitely, except that it’s not. It’s just rotating. This is an incredibly powerful illusion.
For a long time, people thought the Ames window illusion worked because we live in physical spaces built out of rectangles and right angles. However, when researchers showed the Ames window illusion to people who lived in rural areas without many rectangles around, they found that both urban and rural subjects saw the illusion similarly. This suggests there must be something else going on.
The trapezoid is built in such a way that no matter how it rotates, the length of the longer edge is always bigger on the back of your eye than the length of the shorter edge. If there are no other clues available in your visual field, your brain makes the best guess with what it has to work with. The conclusion? The window always appears to spin away from you.
These visual cues exist regardless of whether the environment is built or natural. Human brains seem to be wired to construct reality this way because that is what the world has always shown us.
Can that also explain this? This is a room that can make things grow and shrink right before your eyes. It’s called an Ames room. The ceiling, walls, floor, and windows are all skewed so that when you view it from one particular spot, your brain builds a false reality. The clues your brain is getting are misleading.
Even when you know how these illusions work, when you know that you’re getting tricked, your perception remains unchanged. Having more knowledge doesn’t really affect the illusion much. That’s one of the most wonderful things about the Ames demonstrations; they are cognitively impenetrable. Your perception works a certain way regardless of your thoughts on other topics.
I mentioned that this illusion only works from this one viewing angle. This kind of distorted view is called anamorphism. Artists have been using anamorphic tricks for centuries. One famous example is Hans Holbein’s “The Ambassadors.” When viewed from a very low angle, a slash of gray becomes a skull.
Now, you may think you’re looking at a chair here, but it’s just a jumble of strings pointing this way and that. This is an illusion called the Ames chair. It’s not as well known as the Ames window or the Ames room, but it’s actually my favorite. It shows how sensitive your brain is to certain patterns, and how if you see a special pattern, you almost can’t help but add meaning to it.
The clue your brain picks out in this one is connectivity. From that special point of view, these edges come together to form neat corners. Your brain calculates that if this were a bunch of separate bits of string, the probability of them randomly forming a chair shape is extremely low. So, your brain concludes that all of these lines are connected.
Interestingly, this idea of connectivity might explain one of the oldest illusions on Earth. When you look up at the night sky, you see shapes emerge from the stars, known as constellations. Different cultures have connected the sky dots differently, but one that always seems to be seen the same is Orion.
Most of the illusions in this video were invented by a guy named Adelbert Ames. Around 1910, Ames was studying to be a lawyer but decided to pursue art instead. He studied how the eye senses the world to create more realistic art. However, he ended up designing a series of elaborate demonstrations to unlock the secrets of how we see the world.
Most of Ames’ illusions only work when viewed with one eye from a very specific spot. This is why they work so well in video, as the camera essentially views the world with one eye. As powerful as these illusions are, if you view them with two eyes or move around, they wouldn’t work. They show us a lot about how our visual system can break down, but they also demonstrate how amazing our visual system is when it gets all the information it needs.
Now, let’s discuss one last set of visual cues for size and distance, which only work because you have binocular vision. Hold up two pencils or pens, one in front of the other. When you focus on the rear object, you see a double image of the front object. Close one eye at a time, and you’ll see that your right eye sees the left image, and your left eye sees the right image. Focus on the closer one, and suddenly the back one is doubled.
When looking at a fixed point, your eyes move individually so that point hits the center of each eye. The closer an object is, the more extreme the effect. Your brain unconsciously compares the pictures from each eye and uses that as a clue for distance. You also have clues like texture and parallax, which help you judge what you see.
We build our picture of reality from these bits and pieces of clues, not the full picture. Most of the time, that incomplete information is good enough to build an accurate model of reality. But the Ames illusions show us that sometimes, incomplete information isn’t enough.
There’s an idea that if different people are given the same information, they can end up with very different pictures of what is real and true. But these illusions show us the opposite: when it comes to seeing, evolution has made it so that very different people perceive the world in the same way. And that’s kind of nice to hear these days. Stay curious.
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Optical – Related to sight or the way the eyes perceive light – The optical properties of a telescope allow us to see distant stars more clearly.
Illusions – Things that appear different from reality, often tricking the senses – Optical illusions can make two lines of the same length look different.
Brain – The organ in our head that controls thoughts, memory, and other functions – The brain processes information from our senses to help us understand the world.
Perception – The way the brain interprets sensory information – Our perception of color can change depending on the lighting conditions.
Distance – The amount of space between two points – Scientists measure the distance between planets using advanced technology.
Size – The physical dimensions or magnitude of an object – The size of an object can affect how we perceive its distance.
Reality – The state of things as they actually exist – Virtual reality can simulate environments that feel real to our senses.
Patterns – Repeated designs or sequences – Recognizing patterns helps scientists make predictions about natural phenomena.
Constellations – Groups of stars forming recognizable patterns in the night sky – Ancient astronomers used constellations to navigate and tell stories.
Vision – The ability to see; the sense of sight – Good vision is essential for observing details in scientific experiments.
