Size Constancy

Size constancy is when we instantly and unconsciously infer an object's size given its perceived distance and the size of its image on our retinas. This is shown in the picture below where the man in the background is farther away and appears larger than he actually is in the photo. Our brains are told that the man in the background is farther away therefore we perceive it as larger when in reality its real size compared to the man in the front is smaller.