What are visual illusions, and why do we fall prey to them?

What we call videos are nothing but a fast succession of separates pictures. Our perception makes us see them as one smooth animation.

Similarly, what we see with our eyes is not a single wide-angle picture, but a patchwork of tiny “photographs.” This very page you are reading – your eyes are not scanning it at once. Rather, they move up and down, left and right, each time taking a tiny photography. Your perception patches them all together and lets you see them as one.

If you are not convinced, look at the visual illusion below. It depicts an object that cannot possibly exist in the physical world. However, our perception must make an effort to realize that.

If our eyes scanned the whole image at once, as it seems they’re doing, or if our perception stored the whole image at once, as it seems it’s doing, you would immediately realize that the object above is impossible. But our brain does not work as it seems to work.

Our perception is made of fragments, as depicted below.

Crucially, each fragment is coherent by itself. By analyzing them individually, you cannot spot any incoherence. Only trying to piece them together reveals their incompatibility.

It takes mental effort to realize that, even though each fragment makes sense, their union does not.

In the absence of mental effort, coherence is only checked at the fragment level, not at the “greater picture” level. Hence the illusion that the image depicted in the full picture exists.

End of the excerpt

This is an excerpt from my book “The Control Heuristic​: Explaining Irrational Behavior and Behavioral Change”. You can purchase the book here.