Objects are seen in succession, never simultaneously. Objects differ in both Color and Luminance Objects differ in Luminance, but Color remains constant Objects differ in Color, but Luminance remains constant. Objects differ in achromatic Luminance Objects differ in Pattern only Pattern is created using areas contrasting from the background color (i.e., green) and each other in both Color and Luminance. Pattern is created using areas contrasting from the background color (i.e., green) and each other in Color, but not Luminance. Pattern is created using areas contrasting from the background color (i.e., gray) and from each other in Luminance, but not Color.