Two Zen monks were arguing about a flag being blown by the wind.
One said: ‘The flag is moving...’
The other answered: ‘The wind is moving!’
The prior of the monastery happened to be passing by. He told them: ‘Not the wind, not the flag; mind is moving...’
This short anecdote serves to explain that the concept and perception of motion is sometimes ambiguous. It often occurs that we perceive motion where in fact there is none. An everyday example: you are in a train at a station, looking out of the window at another neighboring train that starts moving. At this instant, doesn’t it feel like your own train is moving in the opposite direction?
In the world of optical illusions, the term ‘apparent motion’ or ‘illusory motion’ (also known as ‘anomalous motion illusion’) is used to define the appearance of movement in a static image. What makes this kind of illusion so interesting is the fact that you are experiencing movement, although you know that the supposedly moving objects are not moving at all.