Optical Wonderful
Interactive Demos
Reading about an illusion is one thing - watching it break as you adjust it yourself is more convincing. These illusion pages include a live, adjustable demo.
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.
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.
AmbiguousNecker 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.
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.
AmbiguousRubin'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.
AuditoryShepard 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.
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.
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.
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.
Color & ContrastChecker 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.
Color & ContrastHermann 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.
Color & ContrastSimultaneous 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.
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.
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.
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.
GeometricCafé 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.
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.
GeometricKanizsa Triangle
Three notched discs create a bright triangle with sharp edges that isn't drawn anywhere. Turn the discs and watch the triangle disappear.
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.
MotionBarber 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.
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.
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.
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.
MotionSpinning 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.
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.
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.
Size & PerspectiveEbbinghaus 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.
Size & PerspectiveMüller-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.
Size & PerspectivePonzo Illusion
Two identical bars look different lengths across converging lines. Measure your own illusion and see how it compares with your Ebbinghaus score.