Fixated images fade from view.
Figure 17. The visual system is most sensitive to change, and adapts (over different time courses) to features that are constant. Here, if you fixate with your left eye (right eye closed), the gray circle above will fade from view in a few seconds. The better you are at keeping your eye still, the faster it will fade.
Open and close your right eye while fixating on the black square. Note that the circle inside your left blind spot disappears immediately (is filled-in immediately) while the gray square takes a few seconds to fill-in and disappear. The blind spot is congenital, and therefore the cortex re-wired itself early in your life to compensate. The filling-in of other parts of the visual works require other mechanisms.