© 2009 Siddharth Jain
In this illusion, a dot is moved rapidly across a computer screen in raster scan order. Even though the dot moves horizontally, we perceive the path to be tilted upwards. Why does this happen? Because of the persistence of vision, we perceive as many as six dots in the display at any time instant, even though only one dot is active. When we consider the six dots, all of them do not turn out to be on the same line. When all possible dot configurations are averaged a tilted line appears, which is what we perceive at the end.
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