The Company It Keeps
Two orange circles, two crowds around them, and one question about size.
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Two orange circles, two crowds around them, and one question about size.
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Comment ça marche — à lire plutôt après avoir essayé
Size is judged against the neighbours
The two orange circles are drawn with the same radius. Among large neighbours the left one looks small; among small ones the right one looks large. Take the neighbours away and the difference goes with them.
The eye does not measure a size on its own; it compares it with whatever is nearby. The effect is named after Hermann Ebbinghaus, who studied memory, and was brought to wide attention by Edward Titchener around 1900. People disagree about how strong it is, and it changes with how close the neighbours are — which is part of what makes it worth playing with.