This is a famous optical illusion, known as the '13 hidden faces'. It is also an attractive piece of art. How many can you find? It is considered that if you can find 10 faces you have normal powers of observation. If you find 15, you have above average observation skills, if you discover 21 or more, you have extremely keen observation skills. The faces that are most obvious are the ones in the foreground, along the path. They are lit up and our eyes are drawn naturally to them. The faces in shadow are perhaps more tricky to observe.

Let me know if you find more, here are my solutions

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You see those embedded spirals of green, pink and blue? The green and blue spirals are actually the exact same colour.

When the green and pink colours are placed side-by-side, they enhance each other’s darker tones, making them look like completely new colours. How we perceive colours is dependant on the light and shadow surrounding them and on the placing of contrasting colours side by side.

In the catacombs of Sicily, there's a creepy child mummy named Rosalia Lombardo who appears to open and close her eyes on a regular basis. Here's how a scientist solved the mystery of this little "sleeping beauty". (Hint: she's not actually undead.)

Can you spot the cat amongst the pigeons? This is Hungarian artist's - Dudolf - latest optical illusion that has some several viewers puzzled. The cause of all this difficulty is likely to have something to do with the way in which the brain processes visual information, by identifying repeating patterns and then using this to automatically fill in the gaps in peripheral vision. This makes it very difficult to spot minor details or irregularities in our visual field without focusing directly on these elements, which means you probably won't see the cat unless you stare straight at it.
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Despite his mother beckoning him to come towards her, this infant hesitates to cross the "visual cliff" – an apparently steep drop that is actually covered by transparent glass. Psychologists in the 1960s found that most infants 6 to 14 months of age were reluctant to crawl over the cliff, suggesting they had the ability to perceive depth. Most psychologists believe that the ability to perceive depth is partly innate and partly a product of early visual experience.

Here's a test you can try to demonstrate how your perception of depth is still live and active. Below are two perfect circles, yet the smaller circle appears distorted. Our brain interprets the converging lines to be adding depth to the screen, as if the solid middle is further aw ...