Persistence of Vision

Persistence of vision refers to the phenomenon where the retina holds the image for 0.04 second after we see the image. This is useful in animation because it is able to create an illusion of movement. This means we are able to skip the gap what which we see the next image so we think the motions seem seamless. But in simple terms.. the speed of light is too fast compared to the brain's opto-chemical reactions therefore the eye can hold the image for a spilt second and when the next images appears, the brain is able to join them together seamlessly. Therefore it goes from still images to moving images. 

Here is a video that explains and it gives examples of optical toys: 

Source: Youtube uploaded by Christine Charters, Feb 6 13, https://www.youtube.com/watch?v=nFHvvj5nD_E

Sources: 

About.com, 2013, http://animation.about.com/od/glossaryofterms/g/pervision_def.htm

Media College.com, http://www.mediacollege.com/glossary/p/persistence-of-vision.html

SlashFlim: GeekBomb, posted by Kevin Kelly, Feb 4 2009, http://www.slashfilm.com/geekbomb-a-brief-history-of-stop-motion-animation/