Strength of the “Rotating Snakes Illusion” was measured by a nulling procedure (veridical motion compensating illusory motion). Independent variables were the luminance levels of the asymmetric grey steps embracing the black and white anchor steps in the luminance sequence.
Revision 2016-11-17: different colours in plot
Revision 2016-12-09: made screenshots public, corrected typo in one author's name