However this is just an example of looking and reconstructing something that we are used to and have seen many times. It is intriguing to find out what processes take place when a visual illusion is being observed. People’s perceptions are called illusion when they experience a stimulus pattern in a manner that’s seems incorrect. For example when you look at the Hermann grid (appendix 1) you begin to see fuzzy spots that are not there. It is suggested that our knowledge can not overcome the illusion, because it operates at a more basic, sensory level. Therefore when you look at the image you start to use your conceptually driven process which is not what is needed in order to stop seeing the ‘fuzzy’ spots at the intersections. This is therefore an example of data driven processes and thus demonstrates the importance of data driven processes.
Visual illusions demonstrate to us that the central nervous system does not simply record events. The system, instead, involves complex processes for ‘detecting, integrating and interpreting information about the world in terms of what we already know and expect’, Zimbardo, McDermott, Jansz and Metaal (1995). This therefore shows that what we see goes beyond the present physical stimulus properties. Even though these processes usually occur without effort and are also helpful in decoding the world around us does not mean that they are simple and error-free. Conceptually driven processes do succumb to errors. Our knowledge and previous experience can in fact fool us into seeing what does not exist.
A good example of this is the Kanizsa’s triangle (appendix 1). It is an example of illusory contours whereby we see something that does not actually exist. The circles have indents of 45 degree angles and there is a broken outline of a triangle this gives the illusion of another triangle. We try to make sense of the images by trying to look for something we are familiar with. Our past experience and knowledge of what a triangle looks like makes us see a triangle in this image, thus we have made sense of it. Coren (1972) Coren and Porac (1983) argue that we create the subjective contours because we see simple, familiar figures in preference to meaningless, disorganised parts. The simple figure in the illusion being the triangle that does not exist. If we did not see this triangle the illusion would be meaningless to us, yet our conceptually driven processes constantly seek understanding of an image.
A British psychologist, Richard L. Gregory studied a man by the name of S.B. in the 1960’s. S.B. had been given the gift of site after spending all his life blind, having been born that way. Gregory wanted to look at how S.B. perceived things for the first time as babies, who also experience sight for the first time can not help to explain what they see. It was interesting to find that S.B. failed to be misled by illusions such as the Herring illusion, (appendix 1). This suggests that he was only looking at the stimulus input and obviously could not look to knowledge and past experience to understand the image. It must mean the conceptually driven processes are learned rather than innate.
Ambiguous pictures offer another challenge for conceptually driven processes. An example of an ambiguous illusion is the face/vase picture created by Edgar Rubin (1915) (appendix 1). When looking at the picture you may find that your perception of it often switches from the vase to the two pictures of a face. When you look at this ambiguous picture and others like it the data remains the same while the interpretation of it varies. It seems there must be a strong conceptually driven processing component in such perceptions. Therefore higher levels of perceptual interpretation appear to be continually constraining and guiding the lower levels of image analysis.
Having said that it does not mean that conceptually driven processes are not needed, as they clearly are. If this process did not exist then what we see each day would be a new experience and trying to interpret what we see would be a long and arduous task. We rely on past experience and knowledge in order to make sense of what is shown to us. Visual illusions help to demonstrate its importance as it shows that we try to make sense of the illusion. Even though we can not get over some illusions fooling us it does show the basic need to understand. Another point to make is that once an illusion is seen, every time we look at it we can see it, we are no longer fooled thus our conceptually driven processes have taken over and looked to past knowledge.
It is thus widely believed that both conceptually and data driven processes work together. An example of this would be to look at the phrase ‘Paris in the the spring’ in a triangle (appendix1). When looked at for the first time your expectation of what the phrase says means that you miss the fact that the word ‘the’ is repeated, (conceptually driven processing). This perception dominates the information actually available in the stimuli (data driven processing).
So far we have looked at what conceptually driven processes are and some examples of how it interacts with our interpretation of visual illusions. Basically it can be concluded that the key to perception is what we expect to see. That is to say the visual illusions highlight the fact that when we perceive things we interpret according to an existing schema we may have for it, or similar to it. Conceptually driven processes allow us to perceive objects, situations and many other things effortlessly and without much thought. Without this process we would have to rely on simple pieces of information that would not make sense at all when put together. It would not be a nice thought that every time we walk into the living room we would not be able to recognise it as a living room because we have no conceptually driven processes. This process is vital in order to function properly in society. Although visual illusions point out some flaws in the process as mentioned before these flaws in fact demonstrate its importance in every day perceiving.
Appendix 1
Kanizsa’s Triangle
Herring Illusion