Size Constancy

Size constancy is the idea that while our distance from an object may vary, we perceive that object as having a constant size.

A real life example is whenever you are looking at a ball on a soccer field. If you are far away from the ball on the field, it may appear smaller. However, since you know the actual of the ball up close, you know that the ball has not shrunken as it moves farther away, but it is just the perception of the ball due to distance that causes to appear smaller.

In the example to the left, there are two identical goblets. The one further down the table appears smaller, but we know that it is not because size constancy lets us know it is the same size no matter the distance we perceive it from.