"D.P."
'(<a href="http://www.j-archive.com/media/2009-12-16_DJ_03.jpg" target="_blank">Kelly of the Clue Crew shows an illusion on the monitor.</a>)  Shadows make the images on the left appear convex, & the right seem concave; <a href="http://www.j-archive.com/media/2009-12-16_DJ_03.wmv">turning them</a> upside down reverses the effect due to this, the ability to see objects in three dimensions'
depth perception