Size Constancy

When we see the same object up close and far away we perceive that the object that's farther away is smaller even though in reality they're the same size. This is called size constancy which  is when we perceive objects as having a constant size even when our distance from them varies. One example is in the picture below. The shoe up front seems larger than the one further back but based on our knowledge we already know that both shoes are the same size, our eyes are just perceiving them as different.