Quick – which of these lines is longer?
If you said the one on the right, congratulations! You’re wrong, of course, but your brain is working perfectly well. This is an example of an optical illusion, an image specifically created to trick your brain. You probably saw a lot of these as a kid, and you may have even thought they were fun. I know I did. I remember finding optical illusions in books, learning about the trick, and then quizzing classmates about them (I was a strange kid). I got satisfaction from knowing the trick to the picture, especially when others couldn’t see the illusion.
Once I got through graduate school, though, I realized that there are a lot of times where knowing the trick just brings up more questions. For example, let’s look at those lines again:
The right one still looks longer, right? But we absolutely know that these lines are the same length! That’s why, to me, the big question is this:
Why does the illusion still work, even after we know the trick?