ABSTRACT
A thoughtful person, relaxing on a hillside and gazing at the rich panorama spread beneath him, may ask many questions about why the visual world appears as it does. He may notice that there is an infinitude of dimensions of variation between parts of the landscape shapes, sizes, colors, textures, brightnesses, distances, etc. He may also discover that he can apply a multiplicity of descriptions to the scene, using alternative categories and subcategories to capture what he experiences. Whatever description he chooses, though, admits the same inexhaustible question What are the sources of the perceived characteristics of the visual world?
