This is one of the greatest books ever written on the subject of sense-perception. It's a masterpiece not just in psychology but in philosophy. Against the view that perception involves taking in raw data and then doing a lot of internal construction and inference to build up an internal image representing the world, Gibson defends a more Aristotelean, direct-realist view that our senses enable us to perceive directly the information that is available in the external world. Gibson calls this an "ecological" approach to perception. He's particularly interested in our perception of motion, and of our ability to perceive changes in our own position. This summary doesn't do justice to the richness of this book.