Where the facts come from
Every factual claim on this site links to its source. This is the full list.
How we checked
We only use expert sources: Michael Bach’s website Optical Illusions & Visual Phenomena, Encyclopaedia Britannica and the Exploratorium in San Francisco. Each fact was written in our own words alongside its source. Our build script stores the source text and, for every fact, checks that the key words and figures really appear in it. 84 of 84 checks passed when this site was last built (31 Oct 2026). Where we couldn’t find one of those sources saying it, we left the claim out.
The games
Measure the Trick, Same or Different? and the Ames Room Walk are our own drawings and code; the explanations on the reveals link to the pages below. In Same or Different? the computer picks the real sizes at random and always reports them truthfully. The quiz answers come from the pages below.
All sources (23)
- Britannica: Adelbert Ames, Jr. (1 fact)
- Britannica: Hermann Ebbinghaus (3 facts)
- Britannica: Illusion (4 facts)
- Britannica: Moon (natural satellite) (2 facts)
- Britannica: Müller-Lyer illusion (1 fact)
- Britannica: Space perception (1 fact)
- Exploratorium: Ames Chair (Science Snack) (2 facts)
- Exploratorium: Distorted Room (3 facts)
- Exploratorium: Looking at the moon (3 facts)
- Exploratorium: Size and Distance (Science Snack) (8 facts)
- Exploratorium: Size and Distance exhibit (1 fact)
- Michael Bach: Ames window (4 facts)
- Michael Bach: Delboeuf illusion (4 facts)
- Michael Bach: Dynamic Ebbinghaus illusion (2 facts)
- Michael Bach: Ebbinghaus illusion (6 facts)
- Michael Bach: Jastrow illusion (5 facts)
- Michael Bach: Moon illusion (9 facts)
- Michael Bach: Müller-Lyer illusion (8 facts)
- Michael Bach: Shepard’s “Subterranean Terror” (2 facts)
- Michael Bach: Shepard’s “Turning the Tables” (2 facts)
- Michael Bach: Sine illusion (3 facts)
- Michael Bach: Size constancy (5 facts)
- Michael Bach: T-illusion (5 facts)