Cool optical illusion–cross your eyes and try to align these circles


Try and cross your eyes to make the top gridded circles overlap. Give up? Try doing it on the bottom ones that are surrounded by the border.

A lot easier, right? The square surrounding the circles helps your eyes stabilize as you cross them.

Free fusion optical illlusion vergent eye movements

From Blake 1989

Also notice how your eyes process the diagonal lines themselves. Your brain is receiving drastically different signals from each eye creating a state of binocular rivalry, where your perception often alternates between the signals received from one eye and the other.

If you’re interested in this phenomena and learning a theory about it’s neural underpinnings check out the paper where I came across it.


Blake, R. A neural theory of binocular rivalry. Psychol. Rev. 96, 145-167 (1989).

One Response to “Cool optical illusion–cross your eyes and try to align these circles”

  1. I did vision therapy for a year and while I still have very unstable depth perception, I was delighted to find that I could, with effort, “do” these circles. I presume that one is “supposed” to see three circles with the center one being a combination of the smaller circle super-imposed upon the larger one? At least that is what I see. I have no idea if this what “free fusion” is expected to produce or not. The upper circles did waver somewhat, with the smaller circle being somewhat unstably inside the larger one compared to the lower boxed-in circles. Fascinating!


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: