Duck & Bunny
This picture of a bunny and a duck(depending on which way you see it). Depending on how you see it is how your codex interpreters the image. Your codex detects stuff on a picture like the direction the object is facing and other details. This is of course the top layer of your codex the visual part of your eye. All of the info that your top codex detects goes to the lower levels that detect direction changes in the corners. The final part is when they register what you looking at like if you were looking at your friend this region is the part that tells you that you are looking at that friend.
Stewart, Ian. "New Statesman." Now You See It, Now You Don't: What Optical Illusions Tell Us about Our Brains. N.p., 7 Jan. 2014. Web. 12 Mar. 2015.