It would be difficult to go directly into specific studies without a general introduction of some background knowledge on visual attention. So in this section, we first introduce concepts of visual attention as well as various mechanisms of attention. Secondly, we present a brief introduction of the HVS and of different types of eye movements as well as the technique for measuring eye movements, i.e. eye-tracking. Finally, we introduce some typical state-of-the-art computational models of visual attention.