Some Biology

Human Eye

 Our eyes offer one of the five specialized means by which our mind is able to form a picture of the world. The eye is a remarkable instrument, having certain characteristics to help us process the light we see in such a way that our mind can create meaning from it.

The Persistence of Vision

The term persistence of vision has come to be seen as inadequate to fully describe this very complex physiological reality, it remains a standard expression and, as such, it serves as a useful metaphor. Whenever light strikes the retina, the brain retains the impression of that light for about a 10th to a 15th of a second (depending on the brightness of the image, retinal field of view, and color) after the source of that light is removed from sight. This is due to a prolonged chemical reaction. As a result, the eye cannot clearly distinguish changes in light that occur faster than this retention period. The changes either go unnoticed or they appear to be one continuous picture to the human observer.

How It Matters

   We use this fundamental fact of the way we see is to an advantage, You may remember making little “flip books” as a child. They worked on this same principle: the more images per second, the smoother the picture. Same way a motion picture creates an illusion of a constantly lit screen by flashing individual photographs in rapid succession. Even though the movie screen appears to be constantly lit, it is in fact dark part of the time. 

Television uses a form of intermittent light impulses to literally build the picture we see. If an image can be built up quickly enough, the eye will be unaware that this process is even occurring