This is a book about how we see. How do we see the environment around us? How do we see its surfaces, their layout, and their colors and textures? How do we see where we are in the environment? How do we see whether or not we are moving and, if we are, where we are going? How do we see what things are good for? How do we see how to do things, to thread a needle or drive an automobile? Why do things look as they do?
This book is a sequel to The Perception of the Visual World, which came out in 1950. It is rather different, however, because my explanation of vision was then based on the retinal image, whereas it is now based on what I call the ambient optic array. I now believe we must take an ecological approach to the problems of perception. We are told that vision depends on the eye, which is connected to the brain. I shall suggest that natural vision depends on the eyes in the head on a body supported by the ground, the brain being only the central organ of a complete visual system.
When no constraints are put on the visual system, we look around, walk up to something interesting and move around it so as to see it from all sides, and go from one vista to another. That is natural vision, and that is what this book is about.
The textbooks and handbooks assume that vision is simplest when the eye is held still, as a camera has to be, so that a picture is formed that can be transmitted to the brain. Vision is studied by first requiring the subject to fixate a point and then exposing momentarily a stimulus or a pattern of stimuli around the fixation point. I call this snapshot vision. If the exposure period is made longer, the eye will scan the pattern to which it is exposed, fixating the parts in succession, unless the subject is prohibited from doing so. I call this aperture vision, for it is a little like looking at the environment through a knothole in a fence. The investigator assumes that each fixation of the eye is analogous to an exposure of the film in a camera, so that what the brain gets is something like a sequence of snapshots.
The headrest of the laboratory prevents the observer from turning his head and looking around, which provides what I will call ambient vision. It also, of course, prevents him from getting up and walking around, which provides ambulatory vision. Are these forms of vision? I suggest they are; in fact, they are the kind of vision we