We’ve all encountered optical illusions at one point or another; but the thing you’ve likely wondered is: How do they work? How do they trick us into seeing something different from what is actually in front of us?

While nearly all optical illusions take advantage of the way our minds have learned to interpret the world around us, different types of illusions demonstrate different things about our visual system.

However, here we’ll just be going a bit deeper into the general idea of how our brain can be fooled by visual input.

The Brain-Eye Connection

As smart as our brain is (and it is smarter than many give it credit for), it cannot see on its own, relying on visual input from the eyes. However, the eyes function more like cameras, and aren’t capable of always effectively conveying complex visuals to the brain. So, at times, the brain gets confused.

This confusion can lead the brain to making mistakes like thinking something is moving when it is not, or “seeing” colors or shapes which aren’t actually there.

For one example, look at the image below. 

The two squares marked A and B are the same shade of gray, despite how it may appear. This is due to our brain trying to determine the color by looking at the other squares around them.

Filling in the Blanks

Because of the simple means of communication between the eyes and the brain, sometimes there is information that can’t get accurately communicated, so the brain makes its best guess based on what information it has received from the eyes. Most of the time, it’s correct.

But sometimes those guesses are wrong, due to the imperfect communication.

An Ongoing Mystery

Despite a great deal of research by many scientists into exactly how these illusions work, for many, we don’t know how the brain-eye link creates them. We do know now that the path the information from our eyes takes to get to the brain is rather long and complex, so confusion can arise at any stage of that journey. Generally, illusions in which the confusion arises later in that journey, the less we know about exactly why and how it happens.

However, more research is being done all the time, so maybe one day someone--perhaps even you!--will finally solve the mystery.