"One can then state as a fundamental principle: When two fields have a common border, and one is seen as figure and the other as ground, the immediate perceptual experience is characterized by a shaping effect which emerges from the common border of the fields and which operates only on one field or operates more strongly on one than on the other." - Edgar John Rubin, Danish psychologist/phenomenologist.
How could I've not noticed this? And now that I have, its all I can see! I can't seem to UNsee it! The arrow in the negative space of the "Ex" in the FedEx logo. It almost blinks at me now! Taunting me like "Yeah, I've been hiding here all along, dumb ass." And here I thought I was oh so perceptive; appreciating the minutiae of everyday life...
The positive-reverse optical illusion presents the eye with a choice of two interpretations – both being valid. It’s very interesting and indeed very reminiscent of “Rubin's vase” phenomenon or Gestalt psychology. But I think we’d need to smoke some pot to broach Gestalt psychology and I don't smoke pot. So, there.
And yea, I know - you've all seen it, you all knew it was there and I'm the ONLY one who never noticed it. Sure. Right.
See: A wonderful interview with the man who created this work of art in 1994: Mr. Lindon Leader.Below: Edgar Rubin's infamous "vase"