👁 Optical Illusion Test

Objective: On every trial you see two shapes, lines, or circles labelled A and B, and you say which one is bigger — or whether they are the same size.

Why it is harder than it sounds: Each pair is surrounded by a classic optical illusion — arrow fins, converging rails, rings, or clusters of circles. Sometimes the illusion pushes you toward the right answer. Sometimes it pushes you toward the wrong one. You are never told which.

Equal-size pairs: With this setting on, roughly one trial in five shows two shapes that are exactly identical, with the illusion still working on them. These are mixed in without warning, so you cannot tell an equal pair apart from a very close one until you answer. Turn the setting off in Advanced Settings if you want a straight A-or-B test.

How to play:

• Click A larger, Same size, or B larger
• Or use the keyboard: A, S and B, or the left, down and right arrow keys
• The bar at the top shows how long you have left on the current trial
• If the timer runs out, the trial counts as a miss and the test moves on

Reading your score: Accuracy is how many you got right overall. The Illusion Effect is the gap between your accuracy when the illusion pointed toward the true answer and your accuracy when it pointed away, and it uses only the trials where one shape really was bigger. Both trial groups are built to contain the same illusions and the same range of size differences, so that gap reflects the illusions rather than one group happening to be easier. Equal pairs are scored separately, since they are neither for nor against the truth. The breakdown also shows your accuracy on each illusion on its own, which is usually where the interesting pattern is.

What the score does not tell you: your result belongs to the settings you chose. Difficulty, time per trial, illusion mix, whether equal pairs were included and whether the reveal was on all change the number, so two sessions are only comparable if they were set up the same way. The reveal in particular teaches you to see past each illusion as you go, so later trials partly measure what you picked up during the test rather than how you started. Time pressure feeds in too: at two or three seconds, a wrong answer can come from not having looked properly rather than from the illusion. And on equal pairs, some people are simply more willing to answer "same" than others, which affects that figure independently of what they saw.

Tips:

• Look at the shapes themselves, not the decoration around them
• On the line illusions, try to ignore the fins and rails and compare the ends
• Turn on Hard mode once the differences start feeling obvious