@mpanhans @kims That *is* the good explanation. We only really see detail in a very small region of our vision called the fovea. Everywhere else, we can generally detect motion, brightness, and sometimes color, but the visual acuity is somewhere in the 20/800 neighborhood. Our brain fills in the rest of what we think we see from the edges of the fovea and from memory of what was there before. The pattern here is coarse enough to be picked up by the edges of the fovea, and the dots are spaced far enough apart the edges don’t pick them up.

Our vision system lies to us about detail, color, size (a baseball you’re trying to hit literally looks bigger than it is), timing (you can never see your own eyes move in a mirror due to a phenomenon known as saccadic masking; among other things, it actually causes our perception of time to run backwards briefly), and much more. ~95% of what you think you see at any given moment is faked by your brain.