The Stepping-Feet Illusion features two rectangles apparently moving like a pair of stepping feet, but they're actually moving at the same constant speed. The illusion is broken when the striped texture is removed [read more:

There seems to be an ever so slight deviation

The Stepping-Feet illusion was discovered by Dr. Carl Stepping and Dr. Helga Feet.

If you move the video frame-by-frame you’ll see that they are not moving at a constant speed

Just focus on two boxes. The illusion will disappear

Because we notice the yellow moving when it crosses the black (too hard to see when it crosses the white) and the opposite is true of the dark blue (too hard to see crossing the black, easy to see crossing the white). Human vision is based on contrast.

If you focus hard enough of the blocks you can make the lines disappear

Sadly, several medieval court entertainers in Utrecht were executed after showing this trick to their patrons using an early copy of Windows 95.

It's probably been studied, but I'm wondering where the breakdown of mixture of internal calculus and visual processing pass the tipping point and create these illusions.

what is the scientific basis for this

Awesome