Our brains sure are tricky lumps of fat. They work with a kind of top-down/bottom-up processing.
Bear with us.
To make sense of the world, your brain sees something (that's the top-down processing) and then digests that image by uniting it with something you’ve already seen (that's the bottom-up processing). Basically, your brain is like a collection of stock images.
That means you’re brain can be fooled. This video shows you how, and it will kind of blow your mind.
Here’s the thing: The brains of schizophrenics aren’t fooled by this optical illusion, Wired