Even though the eyes of a young baby may work fine, its brain has no idea what to make of visual stimuli. And some of that confusion never goes away.

In order to realize what’s going on, the brain has to learn how to translate perceptions into an understandable picture of the environment.

And once it knows, you can have lots of fun with tricks that challenge that knowledge.

The Gullible Brain

Eyes are really nothing but mechanical search bots that prowl the world and ingest everything without distinction. A young child has no idea what to make of what it sees, or even that what it sees has anything to do with what’s going on. Only after repeatedly seeing a parent’s head loom up, the child will gather that this head has something to do with getting fed and cuddled.

Slowly it will learn that a toy it sees is actually there. To a child it’s an earth shattering experience to first reach out for something and grab it and bring it near. And every time it does that, a belief in perceived reality is strengthened. Soon it forgets that its understanding of reality is based entirely on belief.

Because the eyes take in everything, the brain has to sort information into categories and patterns. And it has to assume all kinds of missing bits. A child has to learn that an item that’s covered with a towel isn’t gone, or that mama’s head doesn’t get bigger, she’s only coming closer.

Perspective

Perception of depth in real life is normal but it took humanity a long time to understand how it happens, and how to reproduce it. Duccio di Buoninsegna (1310) painted The Last Supper without perspective. Less than 200 years later, Leonardo da Vinci painted the same scene, but now with the optical illusion of perspective. He achieved this by selecting a point on an imaginary horizon upon which all “horizontal” lines are made to converge.

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Mona Lisa Smiles

But perspective wasn’t the only optical illusion that De Vinci’s excelled in. His famous Mona Lisa painting employs an illusion that has baffled spectators for centuries, and which has only recently began to be understood. Look at the two faces below. Now move away from the screen. You’ll see that the expressions on the faces change. The angry one becomes content and the content one becomes angry.

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The picture of the two faces was created by Phillippe G. Schyns (U. of Glasgow) and Aude Oliva (MIT). They explain, “A hybrid image is a picture that combines the low spatial frequencies of one picture with the high spatial frequencies of another picture producing image with an interpretation that changes with viewing distance.” (1)

The Mona Lisa is so mesmerizing because Da Vinci endowed its smiling face with the minute details of a painful grimace.

Motion Sickness

The very precise colorations of computer screens allows for a recently discovered illusion: that of motion in a static picture. Moving pictures on websites are usually achieved with images in GIF-format. GIFs can show motion by interlacing different frames. But the image below is a JPG (right click to check the properties) and the JPG format only allows one frame. In other words: this picture does not move! It’s all in your head.

In the Journal Of Vision, professor Benjamin T. Backus offers, “We propose that these illusions result primarily from fast and slow changes over time in the neuronal representation of contrast or luminance.” (2)

Dr. Bevil R. Conway and colleagues argue in The Journal of Neuroscience, “Visual neurons respond faster to the higher-contrast white and black elements than to the lower-contrast light gray and dark gray elements.” (3)

Because the JPG image format tends to smudge contrasts, these kinetic optical illusions are usually presented in GIF and PNG formats. If you’re not sea-sick already, stare at these baffling (and guaranteed single-frame) images for a while:

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