What are the motifs in Art and Illusion: A Study in the Psychology of Pictorial Representation by Ernst Gombrich?

Illusion is a recurring idea. Illusion is one of the most puzzling phenomena in the study of perception and by extension, the study of representational art. In the case of an illusion, perception is not dependent on how the receptors in the eye and brain react, nor is it dependent on the object being perceived. That is, a human being is able to make meaning from an image independent of the physiology of either the eye or the image. For example, when children see a picture of a duck in a book and are asked what they see, they will answer, "A duck."