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# Create an Optical Illusion

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Author: Janice VanCleave

### What You Need to Know

An optical illusion is when something appears different from what it really is.

### How Do Optical Illusions Work?

What we see involves more than looking at something with our eyes. Sometimes, what we see is not what actually exists. The eyes send messages to the brain about the object viewed, and the brain interprets the message. An incorrect interpretation may cause you to "see" a misleading image, which is called an optical illusion.

### What Does This Have to Do with Creating Optical Illusions?

One type of optical illusion results from mistaking something due to the influence of background patterns. For example, look at the figure below. Which of the middle circles is larger, A or B? Circles A and B actually have the same diameter. However, what you see is that circle A, which is surrounded by small circles, looks larger than circle B, which is surrounded by large circles.

The figure below is another example of an optical illusion. Look at lines A and B in the figure. Are the lines curved or straight? Use a ruler to measure the distance between the lines at various points along the lines. The distance is the same, proving that lines A and B are actually straight and parallel. The radiating lines cause the image to appear as if the straight lines are curved.

### Real-Life Science Challenge

Why do you see things in three dimensions? The images seen by both your eyes overlap. This overlapped image is sent to the brain. It is the brain that interprets the message as being three-d imensional. This ability to recognize 3-D objects is called depth perception. Over time your brain stores information about how three-dimensional objects look, such as the shading on different sides of an object. While it takes two eyes to see in three dimensions, if you close one eye and look at a tree, or any other three-dimensional object, it still looks 3-D to you. This is because your brain is using stored information to interpret the message sent by your eye.

### Experiment

Now, start experimenting with creating your own optical illusions.

Hints

• Angles and background shapes can change depth perception.
• Flipbooks are a type of optical illusion.
• Colors can be used to create a 3-D picture.