What is meant by 'the grand illusion'? - Chapter 6

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.

Filling in the gaps

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:

1. 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 are used for this.

2. The gaps are filled to a higher level of the visual system and this is more conceptual in nature, instead of a picture being filled in. This is called 'symbolic filling-in'.

3. The brain does not need to fill in gaps. The latter is the most skeptical vision.

Ramachandran states that if people see two vertical lines (one above and one below the blind spot), they still think that the vertical line continues. In addition, Ramachandran has shown that gaps in color and movement are also filled in by the brain.

Change blindness

Research shows that people often do not notice changes in images when they have to make an eye movement, for example when they first have to look at a picture on the left and then look at a picture on the right. In this experiment, parts of the surrounding text were altered during a saccade (here an outward movement of the eye was measured with certain equipment) and these changes did not notice the people. An eye movement ensures that we can only rely on our memory to determine changes. Apparently our memory is not perfect and we do not always have a stable and detailed picture of the world in our consciousness. It does not even appear to be necessary to use two different pictures. It is also possible to shift a picture a bit and in the meantime make a change in the picture. Then, people do not notice the change either. With change blindness, attention is needed to notice changes, but the question is whether to focus attention is sufficient, as changes are more likely to be detected if subjects are attending to the part of the image that changes. Probably this is not the case because the phenomenon does not disappear when people turn their attention to an object, picture or event.

'Inattentional blindness'

Mack and Rock state that conscious perception depends on attention. They came to this conclusion by examining 'inattentional blindness'. Inattentional blindness means that there is no conscious perception when something is not being payed attention to.

Theories about vision

These experiments tell us that there is probably no such thing as as a 'steam of vision'. Seeing is probably not a process of building detailed representations that can be used to compare details. We apparently do not store as much information as we thought, otherwise change blindness would not exist. Yet we feel that there is continuity when we look at the outside world. We do not feel that we see loose pieces, but that vision continues, flows.

Simons and Levin say that we have a rich visual experience when we focus on something. From that we extract the meaning or gist of the scene. Our perceptual system assumes, however, that the visual details have not changed. We therefore do not observe any changes. This creates a phenomenal experience of continuity without too much confusion.

Rensink believes that people can never have a complete representation of the world. We only make a representation of an object when it is needed, but we do not have a representation of it everywhere. O'Regan agrees. There is no need to store large amounts of visual information because we can use the world as external memory as 'the best model'. He does reject that we need internal models at all: the visual world is not something we have, but what we do.

O'Regan and Noë believe that seeing has nothing to do with building internal representations of objects. They are in favor of a sensorimotor theory of vision and visual awareness. They argue that traditional theories can not explain how internal representations lead to visual awareness. They ignore this problem by saying that seeing is not building models but an act to explore the environment. An organism has the experience of seeing when it develops the skills to extract visual information from the world. Interaction with the visual information is done through physical movements, blinking and other actions through which you 'visually manipulate'.

What you see then is not a picture of the world but information that requires further exploration. If you stop manipulating the world, when you do not interact, you see nothing. The inconsistency of the stream of vision and the assumption of an internal stream of images and representations is assumed by the results of filling-in, inattentional blindness and change blindness. The most extreme view that you can take is that the entire stream of vision is an illusion.

Resources: Blackmore; Susan. (2010). Consciousness, Second Edition An Introduction. Abingdon, Oxon: Taylor & Francis.