Size Constancy

Size Constancy refers to the fact that our perceptions of the size of objects are relatively constant despite the fact that the size of objects on the retina varies greatly with distance. The is also an allusion known as the Ames Room. The room appears to look like a normal square room, but it is actually a trapezoid shaped room. Two people stand at each corner on of the room. The one person appears to look very big and the other looks very small. This is a very neat trick.  This video shows the room. 
    This video explains it very well.

    This video explains it very well.