What does it mean to see? Is visual experience an illusion? The term 'grand illusion' arose as a result of research into 'changing blindness' and 'inattentional blindness'. The term 'the grand illusion' stands for the idea that the richness of our visual world is an illusion. Alva Noë states with his 'new skeptism' that the brain builds an inner model of the world, so that we are actually misled about the nature of our experiences. An illusion is not something that does not exist (like a fairy or a spirit), but something that is not what it seems to be.There are two types of theories about visual experience. The first idea is that there is a stream of conscious visual impressions that must be explained. The implication of this is that there is an infinite number of parts at any moment in an infinite visual stream. The second idea is that seeing means having internal mental pictures; the idea that the visual world is represented in our heads. This idea is at least a few centuries old and Leonardo da Vinci was the first to describe the eye as a 'camera obscura', a dark room in which an image of the world was projected. James says we can not take in everything we see while looking around. Yet we are not aware that we have looked over things. How is it that we do not perceive these 'gaps'? In vision, the brain will fill in the missing parts themselves. Another possibility is that it is not necessary to fill in the holes, because the gaps stand for a lack of information.There are all kinds of visions about gaps:The brain actually fills in all the details so that a complete image is created in the brain (or in consciousness?); this is called 'isomorphic filling-in' and probably takes place at low levels of the visual system. As we have already seen, Koch states that active processes such as completion...