Size Constancy

The size of an object's image on our retina changes as the distance of that object from the eye changes -- the farther away it is, the smaller the resulting retinal image. On the other hand, our experience shows that, within certain limits, an object appears to remain about the same size to us regardless of its actual distance. For example, as we approach a friend from a distance, our perception of the friend's size does not change very much, even though the retinal image of the friend (the image cast on the retina) is steadily becoming larger. This tendency for the perceived size of an object to remain relatively unchanged, despite genuine c …