The illusory upwards movement is the motion aftereffect. An example of a visual contingent aftereffect is the McCollough effect. Second-order motion produces a weaker motion aftereffect unless tested with dynamically flickering stimuli. The motion aftereffect is believed to be the result of motion adaptation. In either case, an aftereffect may occur. This particular motion aftereffect is also known as the "waterfall illusion". This waterfall influenced Robert Addams to write a paper in 1834 about the motion aftereffect. It is an aftereffect requiring a period of induction to produce it. This form of the motion aftereffect is known as the "spiral aftereffect". Mid-competition, she suffered from serious feet pain as an aftereffect of the surgery. This device is a well-known example of the motion aftereffect. It then requires a "test stimulus" on which the aftereffect can be seen. He has been tortured, and begins speaking gibberish to her, an aftereffect of the neurodrive. This vivid color aftereffect can last for a minute or more.