Ten classics, drawn live. Look first, then press the button to see the truth.
Are the long grey lines sloping?
They are perfectly straight and parallel. The offset black and white tiles, with the thin grey mortar between them, confuse the edge detectors in your visual system, which tilt each line slightly.
Which line is longer?
Both are exactly the same length. The arrow tips make your brain read the top line like a near corner and the bottom one like a far corner, so it rescales them.
Which gold circle is bigger?
They are the same size. We judge size by comparison: next to big circles the gold one looks small, among small ones it looks big.
Count the black dots.
There are none: every dot is white. Dark spots flash in the dots you are not looking straight at, because of how cells in your retina respond to light and dark around them.
Are the rings turning?
Nothing moves. The repeating dark-to-light steps trigger motion detectors at the edge of your vision. Look at one ring and it stops; let your eyes wander and they turn.
Stare at the cross for 20 seconds.
A green dot appears to run round the circle and the pink dots fade away. The green is an afterimage, and the fading is called Troxler fading.
Do you see a white triangle?
It has no edges at all. Your brain fills in the triangle because it is the simplest explanation for the cut-out circles and the broken outline.
Is the left square darker than the right one?
They are exactly the same grey. A dark surrounding makes grey look lighter and a light surrounding makes it look darker.
Look at the cross and keep very still.
After a few seconds the soft coloured blobs fade into the grey. Your brain stops reporting things that do not change at the edge of your vision.
Watch the centre of the spiral for 30 seconds, then look at a painting.
The painting seems to swell or shrink. Your motion detectors tire in one direction, so a still picture looks like it moves the other way.
Your brain does not see the world directly: it makes fast guesses from patterns, edges and context. Illusions are pictures built to make those guesses wrong in a predictable way.
No. They are harmless. Animated ones can be uncomfortable for people sensitive to flicker or motion: look away if you feel dizzy.
StereogramsHidden 3D pictures, and a generator to hide your own message.
Ambigram generatorA word that reads as another word upside down, or a mirror-symmetric name.
Agamograph makerA folded flip picture that changes as you walk past. Printable.
Red/cyan 3D artAny painting in real 3D for red/cyan glasses, with your word floating in front.