Vision is the process of discovering from images what is present in the world, and where it is. - David Marr

Vision is a process that produces from images of the external world a description that is useful to the viewer and not cluttered with irrelevant information.

The critical act in formulating computational theories turns out to be the discovery of valid constraints on the way the world is structured -- constraints that provide sufficient information to allow the processing to succeed.

To understand the relationship between behavior and brain one has to begin by defining the function, or computational goal, of a complete behavior. Only then can a neuroscientist determine how the brain achieves that goal.