I'm not sure the central argument fully explains the illusion.
If you can simultaneously see several stars in the sky using your peripheral vision using averted gaze, why not several dots?
I suspect uncertainty plays a part, but image completion from higher-order feedback that complete the lines might drive the illusion more. Put another way, I believe if you remove the gray lines, the illusion ceases to work.
Because stars in the sky is a high contrast visual. That applies here too, I increased the contrast using Photoshop and the illusion is gone, you can see all 12 dots perfectly fine — http://imgur.com/a/G4xR4
I think they are spot on, outside the fovea, contrast detection capability of our eyes dip drastically thereby blending the dots lying outside the fovea with the surrounding grid. Increase the contrast to the point where even the regions outside the fovea can detect it and the illusion goes away.
If you can simultaneously see several stars in the sky using your peripheral vision using averted gaze, why not several dots?
I suspect uncertainty plays a part, but image completion from higher-order feedback that complete the lines might drive the illusion more. Put another way, I believe if you remove the gray lines, the illusion ceases to work.