I made a Blender file that has the white square on the black background for you. Looking at it in action may help you get an idea of what goes on with fields:
Chapter 12download pack.
When you have fields turned on, two images are rendered and merged. One image represents the time during the first half of the frame. Every other line is rendered. The other represents the time during the second half of the frame. Then the alternating lines are rendered.
When both fields ...