This is your brain; isolated from the world inside your skull.
Your senses provide its only clues to what's going on out there, creating your perception of the world via what you see, hear, smell, taste, and touch.

The Human

Brain

As we will soon find out, however, seeing is not always believing—meaning that sometimes, your brain ends up filling in the gaps to create an image that isn't even there.

An optical illusion of rotating snakes.
"Rotating Snakes", created by Akiyoshi Kitaoka (2003).

Take the optical illusion to your right, for example, where each "snake" appears to be in perpetual motion despite the image being completely static.

Confused? So is your brain.

Here, some scientists suggest that the small, almost imperceptible rapid movements our eyes make—called saccades—are being smoothed out by the brain to give us a single picture that perceives motion when there is none.

Others say that the image is sending so many pieces of information to our retina that our visual cortex—the region of the brain that processes visual information—becomes overwhelmed in its confusion.

Whatever the explanation may be, it's clear that the connection between our eye and brain isn't as straightforward as it initially seems.

The following pages will explore several optical illusions to answer one critical question: how exactly does our brain take the limited information from our senses to construct a trustworthy reality?