Chubb illusion (variant)

When the dark and light segments of both the inner and outer disks are not aligned, the gray portions of the inner disk look different (more contrast) than when they are aligned (use the link below to shift from the unaligned to aligned configuration to see this effect). The original version of this illusion was published in 1989 (Chubb, C, Sperling, G and Solomon, JA (1989) Texture interactions determine perceived contrast. PNAS 86:9631-9635).