ABSTRACT
Throughout this book we have emphasised the applied, functional character of vision. Vision exists in humans and other animals because it is an aid to survival. The properties of vision are those needed to carry out significant activities such as seeking food, shelter, and sex, so that individuals can survive and reproduce. In the case of humans, significant activities are not necessarily restricted to the primary demands of survival and reproduction. We may seek a variety of sources of visual stimulation, many of which are cultural products nowadays. Some of these, like painted pictures, may be as old as the human race itself. Others, such as photographic or television images, are more recent. Writing and printed text are visual stimuli of particular complexity, because the shapes bear little visual relationship to the objects or meanings they convey.
