Size Constancy

Size constancy is one type of visual subjective constancy. Within a certain range, people's perception of one particular objects' size will not change, regardless of changes in distance or the video size change on the retina.

This man in the front appears to be the same size as the man behind when viewed at different distances from the viewer. However, when the man from behind is brought forward to the same location, he looks considerably smaller (assuming the image the image did not change). Clearly, our perception of size constancy is based on the ability to take depth information into consideration. In reality they are the same size, but our perception deceives us.