This optical illusion plays with your peripheral vision and as it turns out, people have not honed in this skill as well as some other species. For example, if you focus on one word the rest of the words around it may look a little blurry. In most cases, the brain will make up the visual difference often leading to a not so accurate view of reality. This might be why we sometimes see shadows moving in the corner of our eyes.
The image was originally posted online by Japanese psychology professor Akiyoshi Kitaoka and it quickly went viral, it was even picked up by a scientific journal Perception.
If you look at where thegrey lines in the image meet you might be able to make out small, light grey squares. This is because of the contrast detected by the retinal ganglion cellsin the backs of our eyes. Derek Arnold, a vision scientist, claims :
At a non-intersection, you’ve got a strip of grey line and it’s surrounded by a lot of white," Arnold explains. "When you get to an intersection, you’ve got multiple grey lines intersecting, and not as much white." Because there’s less contrast at these intersections with more grey than white, the brain thinks the dot where all the grey lines intersect is lighter than the rest of the grey line and creates the illusion of a faint white square. That can counteract the blurry black dot that is actually, physically there.
Check out the video above to see the optical illusion