I was looking into this when the 12-dot illusion came out, and found an interesting refutation of the receptive field theory regarding a related illusion - the original Hermann grid. I'm not sure if it also applies to the 12-dot illusion, where the illusion seems to be more about foveal/peripheral accuracy.
You can read about it here, and play with a demo:
http://www.michaelbach.de/ot/lum-herGridCurved/index.html
http://web.mit.edu/bcs/schillerlab/research/A-Vision/A15-2.h...