Without the perceptual process s of Size Constancy the world would be like Alice in Wonderland.
When I look at the students in the rear of my on-campus class, I do not perceive them as being any smaller than those in the front row (even though they are much smaller on my retina). My brain preserves their size (makes them bigger) but places them far
This perceptual finagling with size and distance can be seen in the illustration of the Theatre Scene on the next page.
Line C-D, which is farther away (as judged by learned cues), appears perceptually to be larger than line A-B.
In reality, as measured by a ruler, the lines are of equal length. The perceptual process however, modifies our experience, based on the distance/size trade off. There are also some more neat examples in the notes.
NOTES: Here is an interesting site on size constancy.
NOTES: Here is another good site on size constancy.
NOTES: Still more on size constancy.
NOTES: This is the last one on size constancy.