sentences:  These regularities permit the visual system to use fragmentary information present in the retinal image to draw accurate inferences about the physical cause of the image.For example, when we make inferences from the retinal image, the knowledge that we live in a three-dimensional world is essential to the correct interpretation of the image.Often, we are made aware of the existence of these powerful interpretations and their assumptions when they are in error, that is, when we discover a visual illusion."