This highly original and interesting monograph puts forward ideas on visual processing and representation in the early stages of visual perception, and examines the computational requirements of the system and its psychological performance.Initially the author considers the computational theory of how the maximum amount of useful information about the scene can be registered from the variations in light intensity in the retinal image. He then goeson to address the question of just what it means to say that the visual system measures spatial aspects of the retinal image, and the consequences of the inevitable distortions that are introduced. He believes that the calculation of spatial position within a distorted metric is not trivial and requires dynamic processes with memory and control. Finally, Dr. Wan argues that the strength of the link between the low-level approaches of psychophysics and computational theory and high-level approaches of cognitive visual function lies in the logic of the arguments that indicate the computational need for control. This Essay will be of great interest to researchers in computer vision, perception, cognitive science and cognitive psychology.