Why do we need vision? As it turns out, there are two answers to this question. On the one hand, we need vision to give us detailed knowledge of the world beyond ourselves – knowledge that allows us to recognize things from minute to minute and day to day. On the other hand, we also need vision to guide our actions in that world at the very moment they occur. These are two quite different job descriptions, and nature seems to have given us two different visual systems to carry them out. One system, vision-for-perception, allows us to recognize objects and build up a ‘database’ about the world. This is the system we are more familiar with, the one that gives us our conscious visual experience – and allows us to see and appreciate visual art. The other, much less studied and understood system, vision-for-action, provides the visual control we need to move about and interact with objects. This system does not have to be conscious, but does have to be quick and accurate. Both systems work together in the creation of art.
The idea of two visual systems in a single brain might seem initially counter-intuitive. Our visual experience of the world is so compelling that it is hard to believe that some other quite independent visual signal – one that we are unaware of – is guiding our movements. After all, it seems obvious that it is the same subjective image that allows us both to recognize the coffee cup on our desk and to pick it up. But this belief is an illusion. As work with neurological patients shows us (and this has been confirmed in recent brain imaging studies), the visual signals that give us our experience of the cup are not the same ones that guide our hand as we pick up it up!