Illusion Library

Color & Contrast

"The Dress" (Blue/Black vs White/Gold)

The 2015 photo that split the internet into blue-and-black and white-and-gold. Why it happens, and a poll testing whether night owls really see it differently.

Size & Perspective

Ames Room Illusion

A room that looks rectangular through a peephole but isn't, so two people of the same height look like a giant and a dwarf. Move away from the peephole to see why.

Depth

Anamorphic Chalk and Street Art Illusions

Pavement paintings that only stand up from one spot. Move the viewpoint in the demo to find where a smear of paint becomes a solid box.

Depth

Autostereograms ("Magic Eye" Images)

Hidden 3D shapes in a field of dots. Generate your own Magic Eye picture, with your own word hidden inside, and learn how to see it.

Motion

Barber Pole Illusion

Stripes on a barber's pole seem to climb forever, though the pole only turns. The aperture problem, demonstrated with two windows of different shapes.

Geometric

Café Wall Illusion

Perfectly straight mortar lines between offset black and white tiles look tilted. Change the shift, the mortar colour and the thickness to switch the illusion off.

Nature

Camouflage in Animals (Visual Illusion in Nature)

How camouflage defeats the same edge and shape detection that drawn illusions exploit. Hunt for camouflaged moths on bark in a short game.

Cognitive

Change Blindness Illusion

Two versions of a photo, alternating with a brief blank, differ in one large object, and most people take ages to spot it. Time yourself, then remove the blank.

Color & Contrast

Checker Shadow Illusion

Two squares on a checkerboard, one in shadow, are exactly the same grey, but almost nobody sees it until a bridge joins them. Why the brain reports surfaces, not light.

Depth

Chromostereopsis (Color Depth Illusion)

Flat red and blue shapes that seem to sit at different depths because of how your eyes focus colour. Close one eye and the depth disappears.

Ambiguous

Duck-Rabbit Illusion

One outline reads as a duck facing left or a rabbit facing right. Most people can't see both at once, and what you expect to see decides which comes first.

Size & Perspective

Ebbinghaus Illusion

The same circle looks smaller among large neighbours than among small ones. Measure how strongly it fools you and compare your score with other visitors.

Geometric

Escher's Waterfall (The Impossible Waterfall)

Escher's lithograph of water that flows downhill all the way round a loop and back to the top. Trace the route and find the joint that can't exist.

Size & Perspective

Forced Perspective (Photography Technique)

The camera trick behind holding up the Leaning Tower of Pisa and making hobbits half the size of wizards, and the size constancy it fools.

Color & Contrast

Hermann Grid Illusion

A plain grid of black squares makes grey smudges flicker at the crossings you aren't looking at. The textbook explanation, and why it's probably wrong.

Depth

Hollow Face Illusion

Seen from behind, a hollow mask still looks like a normal face bulging outwards, and seems to turn to follow you. Why expectation beats the evidence.

Cognitive

Inattentional Blindness (The Invisible Gorilla Experiment)

Half the people counting basketball passes miss a gorilla walking through the game. Try a short lab version of the test and see how other visitors did.

Geometric

Kanizsa Triangle

Three notched discs create a bright triangle with sharp edges that isn't drawn anywhere. Turn the discs and watch the triangle disappear.

Auditory

McGurk Effect (Audio-Visual Illusion)

Dub the sound 'ba' onto a face saying 'ga' and most people hear 'da', a syllable nobody spoke. Why seeing a mouth changes what you hear, and why not everyone does.

Nature

Mimicry and Eyespot Patterns

Eye-like markings on butterflies, caterpillars and fish that startle predators or draw attacks away from the head, and the debate over why they work.

Size & Perspective

Moon Illusion (Why the Moon Looks Bigger at the Horizon)

The moon looks huge on the horizon and small overhead, though it's actually slightly smaller on the horizon. The competing explanations, and how to test it yourself.

Motion

Motion Aftereffect (Waterfall Illusion)

Watch a turning spiral for 30 seconds and a still one seems to move the other way. Time how long your own waterfall illusion lasts and compare with other visitors.

Size & Perspective

Müller-Lyer Illusion

Two identical lines look different lengths because of the fins at their ends. Measure how far the illusion pulls your judgement in a one-minute test.

Ambiguous

My Wife and My Mother-in-Law (Old/Young Woman Illusion)

One drawing shows a young woman looking away or an old woman in profile, with the same lines serving both. Labels in the demo help you find the one you're missing.

Ambiguous

Necker Cube

A wireframe cube with no shading that the brain reads as two different solid cubes, flipping between them. Which face looks nearer first? Vote in the poll.

Afterimage

Negative Afterimage (Stare-and-Shift Illusion)

Stare at a strong colour for twenty seconds, then look at a blank surface, and a ghost appears in the opposite colour. A guided timer lets you try it.

Geometric

Penrose Stairs (The Impossible Staircase)

A staircase that climbs forever in a closed loop. Why each flight looks right, why the loop can't exist, and how the idea reached Escher.

Geometric

Penrose Triangle

Three beams that form an impossible closed triangle. Turn a real 3D model in the demo and find the one direction from which it becomes impossible.

Motion

Peripheral Drift Illusion

Still patterns that seem to creep out of the corner of your eye. Switch the brightness ramp to symmetric in the demo and the drift stops.

Size & Perspective

Ponzo Illusion

Two identical bars look different lengths across converging lines. Measure your own illusion and see how it compares with your Ebbinghaus score.

Motion

Rotating Snakes Illusion

Kitaoka's still image of rings that seem to turn on their own. Toggle the colours and the brightness order to find out what drives it.

Ambiguous

Rubin's Vase (Face/Vase Illusion)

A vase or two faces in profile, sharing one outline. A slider changes the size of each region so you can feel the balance tip from one to the other.

Auditory

Shepard Tone (Auditory Barber Pole)

A scale that seems to climb forever but keeps returning to where it started. Play it in your browser and watch the tones that create the endless rise.

Color & Contrast

Simultaneous Contrast Illusion

Two identical greys look different on dark and light backgrounds. Why the brain judges brightness and colour by comparison, from Chevreul's dye works to today.

Motion

Spinning Dancer Illusion

A silhouette that some people see turning clockwise and others anticlockwise. Ours is filmed level, so the usual bias should vanish. Vote and see if it does.

Cognitive

Thatcher Effect (Upside-Down Face Illusion)

A face with its eyes and mouth turned upside down looks grotesque, until you turn the whole picture over and the distortion almost vanishes.