If you stare consistently at movement in a particular direction even for a short time, subsequently viewed
stationary scenes briefly appear to move in the opposite direction. This phenomenon was known to the Ancient Greeks, and has been re-discovered several times. Robert Addams observed the effect in the 1800's while viewing a waterfall at Foyers in Scotland. This demonstration was created from a view of the Falls of Foyers. After gazing at the movie for about 30 seconds (keep your eyes still by fixating on the tree branch in the middle of the falls), stop the movie using the controller, while maintaining fixation. You will see the frozen water drift upwards for a short time.
The motion after-effect (MAE) can be explained by adaptation in visual neurons that respond selectively to moving contours in the image. In the absence of image motion, cells tuned to different directions produce roughly equal responses. Exposure to a particular direction of motion alters the balance of activity in favour of cells tuned to the opposite direction, causing the after-effect.
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