Still motion? Motion illusions and luminance contrast.

The influence of different luminance contrasts and equiluminance on illusory motion in four inducing patterns was studied: enigma, rotating snakes, pinna, and rotating-tilted-lines. At high luminance contrast the Pinna and the rotating-tilted-lines illusions are significantly stronger than at low luminance contrast, whereas the Enigma and Rotating Snakes illusions are stronger at low luminance contrast. At equiluminance along the L-M axis the strength of all illusions is greatly reduced. Data suggest that luminance contrast constitutes one important factor for their occurrence.