How to read your score
Set the slider until the vertical line looks exactly as long as the horizontal one, then tick Show the answer.
- 100%: you were not fooled at all (rare).
- 90 to 99%: a mild effect.
- Below 90%: a strong effect. You made the vertical line noticeably shorter because vertical lines look longer.
Lab studies typically find people overestimate vertical lines in an inverted T by somewhere around 10 to 20 percent, though it varies with the figure and the person.
Try it on others
Ask family or classmates to try without seeing your answer, and compare. More illusions with a built-in check: the Müller-Lyer illusion, the Ebbinghaus illusion and the Ponzo illusion.
