1.1 The Concept of Visual Attention
1.1.1 Selective Visual Attention
In about 300 bc, Aristotle, a famous philosopher and scientist, mentioned the concept of visual selective attention and stated that humans cannot perceive two objects by a sensory act simultaneously . Although people generally believe that they can get much information from their rich and colourful world and become conscious of environmental changes, many experiments have shown that the human visual ability is overvalued. When people as observers look at a scene, they have the feeling of being able to see all the details. However, when a blank field is inserted between two successive nature scenes with some differences, most observers fail to spot the changes. The reason for this phenomenon is that observers' eyes only can focus their attention on a small area of the visual field at a given moment. Consequently, only this small area can be observed in detail. The saccade over the surroundings often means that our eyes are located in a few places longer than others, or more often than others. The eyes will jump from one fixated locations to another in a scene by saccade. Some animals like quadrumanes also have this ability of selective visual attention. The areas that eyes of humans and quadrumanes often gaze at are referred to as fixated regions and the ignored regions as non-fixated regions.
What is selective attention? A definition given by Corbetta  is ‘The mental ability to select stimuli, responses, ...