Field of Science

Can you see this illusion?

Yesterday, Cognitive Daily posted a fairly compelling visual illusion. There is a while disk and a black disk. In the middle of each disk is a circle. The two circles go from black to white back to black in sequence.

Normally, the rules of perceptual grouping would cause you to see the two smaller disks blinking in unison as being related. However, in this case, due to the smaller disks being inside larger disks, most people see the disks blinking out of sequence. That is, you interpret the scene as a hole appearing in the left disk, then in the right disk, then in the left disk.

Both interpretations are correct. It's a matter of what your visual system focuses on. What interests me is, looking at the comments on this post, is that while the vast majority see the alternating blinking, some people only see the disks blinking in unison. One possibility is that they are misunderstanding what they were supposed to see. If there is some small percentage of people whose visual systems focus on different grouping principles, that could be very interesting and be useful in understanding perceptual grouping in the visual system.

So, if you only see the inner disks blinking in unison and don't get the alternation illusion, comment here or send an email to

Try out the illusion here.


josh said...

There was an unfortunate type-o on this post, now fixed. Few to no people normally perceive the two small disks blinking in unison. Do you?

dr x said...

Great illusion, but you could say that they are not "blinking in unison" because they appear and disappear alternately within their respective fields -- i.e, there are never two dots visible on the screen at the same time because one or the other disappears into the surrounding field. When a center dot is visible on the left, it is not visible on the right and vica versa.