Why can your eyes see something that is not there?

Your brain interprets images instead of simply recording them.

Here's the surprise

Two identical shapes can look different because of the surrounding context.

What's really going on?

Vision is an active process. The brain uses edges, contrast, context and past experience to interpret incoming signals.

Many illusions expose useful shortcuts in that process. Those shortcuts usually help us navigate a complicated world.

An illusion does not mean your eyes are broken: it reveals how perception is constructed.

Think about it

Reveal the explanation

Not necessarily. Some visual illusions persist even when you understand the trick.