Persistance of Vision

Persistence of vision can also be known as the theory of human vision. 

It is the unique way the eye holds images for approximately one twenty-fifth of a second on the retina of the eye, after the image was actually seen. When a sequence of images are shown very fractionally close to the next one, its creates the illusion of motion and we don't notice the momentary gap in between each image. In films, we see 24 frames per second, whereas in a cartoon and animation, there is 12 frames. The persistence of vision allows the eye to hold the image longer in the eye before it disappears so that the motion we are seeing looks like one long movement and flows into each other.