A perception game · nothing to read · no counting
Two shapes. Which is bigger? Looks easy.
Your eye judges a shape together with its neighbours, never alone. Tap the bigger shape — or call them the same. After every vote the context dissolves and the ruler shows the true measure.
- Local
- 5 rounds
- 30 seconds
Nothing leaves your browser. Classic illusions, drawn to exact scale on the page. A game, not a vision test.
Play: 5 rounds
Tap the shape that looks bigger. If they look the same, press “Same”. Keyboard: ← left, → right, S same.
Why it happens
The eye is no ruler: it measures the target together with the scenery. The rings around drag the size along (Ebbinghaus), the arrowheads drag the length along (Müller-Lyer), the background and the frame drag too (Ponzo, Delboeuf). That is why the game mixes real-difference pairs among the traps: when the difference is real (over 20%), you catch it — so missing the traps is illusion, not inattention.
Limit next to the claim: the game does not measure your vision and detects nothing medical. Perceived size also depends on your screen.
Method, limits, sources
How it plays: each game draws 5 pairs out of 8 — 3 traps with identical shapes (correct answer: “Same”) and 2 witnesses with a real 22–25% difference (correct answer: left or right, the side drawn too). The score is the number of correct votes out of 5.
Reuse: CC BY 4.0. Credit “Marius Comper — Which Is Bigger? (frozen 3 September 2026)”.