This chapter has so far covered the human hardware for vision. Basic physiological properties, such as photoreceptor density or VOR circuitry directly impact the engineering requirements for visual display hardware. The engineered systems must be good enough to adequately fool our senses, but they need not have levels of quality that are well beyond the limits of our receptors. Thus, the VR display should ideally be designed to perfectly match the performance of the sense it is trying to fool.