Question: Are the disks in the center of the black and yellow rings blinking together, or are they alternating?
Answer: Both!
Blinking together — if you consider light level: The disks have identical light levels, so they are actually shifting from light to dark at the same time.
Alternating — if you consider the contrast between the disks and rings: When the disks are bright, the contrast between the disk and black ring is high, and the contrast between the disk and yellow ring is low. Vice versa when the disks are dark.
Contrast Asynchronies are compelling because our perception of the luminance modulation is in conflict with our perception of the contrast modulation.
Reference: A. G. Shapiro. Separating color from color contrast. Journal of Vision 2008;8(1):8.
Sweet “illusion”, nice explanation and nice execution. I love being able to drag around the mask