Emmert's Law

Emmert's Law encapsulates the visual knowledge that items that are closer to the viewer will appear larger than items that are farther away. Emil Emmert (1844-1811) also studied "afterimages" or images that appear after viewing a bright light for a time, or after staring at an a figure for a time. He noted that an afterimage will appear to have a different size when you switch your visual focus.