Color
Optical illusions have always been a popular method to explain the mysterious workings of the human eye. Among the white circles, you may be bothered by the flickering of black dots that seem to rapidly appear and disappear. There are no actual dots, however, the fatiguing of the rods and cones in your eyes cause them to appear. When you adjust the intensity of the lines, at what point are the dots most prominent? When do they seem to disappear?