The Reversible Ripple

On the left you see a surface wiggling in three dimensions, much like a ripple on a pond. You see this surface as divided into three parts: a bump in the center, and two concentric rings of bumps around it. The dashed lines mark where you see one part stop and the next part begin. Notice that it is almost impossible to see this image as flat, even though the screen on which you view it is undeniably flat. On the right is exactly the same image as on the left, except that it is turned upside down. But notice that the parts you see on the right are completely different. The dashed lines, which used to mark the boundaries between parts, now lie in the middle of the new parts you see. The left and right images might look so different to you that you might not believe that they are the same, just turned upside down. You can prove to yourself that they are by simply turning your head to the side by more than 90 degrees (taking care, of course, not to fall out of your chair). Then you will see that the right image flips to look like the left one did when your head was upright. And the parts you see will flip also. This illustrates that your Visual Intelligence has special rules for constructing parts of objects.

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