Seeing is believing; or is it?

Can you believe what you see? Is whatever you see "real" or "true"? Do you see exactly the same as I do, or as anybody else does? Even if so, does your brain correctly interpret what your eyes (claim to) see?
These may sound like simple or even silly questions at first, but as the examples below illustrate that's not quite the case.
Look at the two images below, for instance (click figures to enlarge). You may be inclined to believe that the height of the gentleman's hat (distance C-D) is larger than its width (distance A-B). In fact, however, distance A-B is slightly larger than C-D! Similarly, on the second figure it may appear that line A-B (ceiling height) is longer than C-D (closet height). That's not the case either! Both lines have exactly the same length. Feel free to measure them if you like...

Now look carefully at the figure below. It certainly looks like the edges are curvy, right? Sorry, as you probably have guessed that's another optical illusion. All the edges in this image are completely straight! You don't need to believe me. If you still trust your eyes better, go grab a ruler or print it out to verify.


It gets trickier. Take a moment to inspect the checkerboard shown in the next figure. Which square is darker, A or B? Square A is obviously darker, correct? Not so, squares A and B are exactly equal, they have exactly the same color! This one is particularly hard to believe, but in this case our own eyes are playing us. I actually measured the RGB values using Photoshop, and for both squares they are 120-120-120. Still not completely convinced? Click here to see the proof.


As if it weren't enough that our spatial perception could be so easily messed up, we can now see that our perception of colors doesn't seem that good either. Another great example of this is illustrated below. This figure shows a negative picture of a Monarch butterfly, and on mouse-over is displays a grayed version of the same picture. Stare at the center of the negative image for about 30 seconds, then roll the mouse over the figure. What do you see?


Amazing, isn't it? Instead of the gray figure, we see a full color version of the Monarch butterfly, even though we are, in fact, looking at a grayscale picture. Try again if you're not fully convinced. The longer you wait before rolling the mouse over, the more vivid the effect is.

Finally, here's one more cool figure. Take a look at the three faces below.


Images A and B look OK, while image C looks horrible, right? What's the big deal? Look more closely (click to enlarge), and you'll see that figures B and C are in fact the same, not A and B. Our brain does not "complain" when we're looking at figure B because, even though the head is turned upside down, the mouth and eyes are still facing "up" as we'd normally expect. As you see, we were fooled once again! This example is presented in the book "Quirkology" by Richard Wiseman. Click here for more info on the "curious science" of quirkology!

The first three optical illusions shown above are from the website Archimede's Lab, which presents tons of other cool illusions as well as mind and visual puzzles. Similarly, the blog Optical Illusions Etc, from where the checkerboard and butterfly examples were borrowed, has lots of amazing figures and definite proof that we really cannot trust anybody, not even our own eyes!!!