The complexity of most virtual environments prevents them being rendered in real time even on modern graphics hardware. Knowledge of the visual system of the user viewing the environment may be used to significantly reduce image computation times. In this paper, we demonstrate the principle of Change Blindness, a major side effect of brief visual disruptions, including an eye saccade, a flicker, or a blink, where portions of the scene that have changed simultaneously with the visual disruption go unnoticed to the viewer. The onset of the visual disruption inhibits visual attention by swamping the user's local motion signals, short-circuiting the automatic system that normally draws attention to the change location. Without automatic control, attention is controlled entirely by slower, higher-level mechanisms in the visual system, that search the scene, object by object, until attention finally focuses on the object that is changing. Previous work in perception-based rendering has exploited human visual acuity, to control detail (and therefore time) spent on rendering parts of a scene. In our experiment we show that if changes in rendering detail occur when there is a visual disruption, then visual attention to the change is dramatically slowed as in natural scenes. Therefore, if the principal is used in dynamic animations the change will have passed through the visual field without notice before the viewers' attention has picked up the change. Our results clearly show that flaws in the human visual system, such as Change Blindness, can be exploited to reduce rendering times substantially without compromising perceived visual quality.