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We are constantly bombarded with sensory stimulation, so much so, that we depend on the brain to provide a way to filter its input. Psychologists call this "top-down" processing, meaning that the cortex (the top) is constantly setting up decision rules about what information to let in or out. It's somewhat like a receptionist who determines which calls reach the boss and which don't. The same top-down systems, however, also create interesting perceptual dilemmas.
Why are you reading about perception in a blog on "fulfillment," you ask yourself? Not to worry-- there's a perfectly good reason. Illusions are fun. Taunting our peceptual apparatus with visual and other sensory tricks turns out to be an endless source of entertainment. Since illusions are everywhere you can keep yourself amused no matter how bored you might be at the moment by playing games with your mind's eye. There's also evidence to show that people who are more open to perceptual experiences, such as illusions, have advantages in their overall psychological functioning. As I've discussed in an earlier posting, keeping an open and flexible mind is not only fun but good for you.
Let's start with an easy and silly illusion that you can practice out the next time you get bored in class or at a business meeting. First, put your fingers together so their tips touch. Then move them apart about an inch, keeping them in line with each other, and blur your eyes a little. A "finger sausage" will appear in the middle. Come to think of it, this might not be the best illusion to perform at a meeting. Instead, you could try the afterimage color illusion where you stare at a colored image for a few minutes and then look at a blank wall. The complementary colors of the image will appear before you.
Now let's get to the part about the moon and the blueberry. One of the most intriguing and universal illusions in existence is the moon illusion. You've experienced this on a clear evening when you can get a good view of the full moon, The moon appears gigantic when it's at the horizon but tiny when it's in the overhead sky. You might think this is because the moon actually is closer when it's at the horizon or because something about the atmosphere alters the way the moon appears at the horizon. However, the sensory cells on your eye's retina at the back of the eye "see" exactly the same image, no matter where the moon is in the sky.
You can easily demonstrate the extent to which people are fooled by the moon illusion by asking the following simple question: You are watching the moon just after it has risen above the horizon. If you were to hold out your hand at arm's length what object would completely cover the moon from view? 1. Blueberry 2. Quarter 3. Golf ball 4. Baseball 5. Dinner plate (or, in keeping with the song, pizza pie). The answer, which you've probably guessed, is 1: blueberry. Most people will guess quarter, and some even will pick choice #5. If you don't believe that this is the answer, try it!
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hy does the moon illusion work? Psychologists don't have 100% certainty on the answer, but there's a pretty good explanation involving another illusion with the exotic name of "Ponzo" illusion. This is not a creation of Bernie Madoff, though he certainly did create an illusion. No, the Ponzo illusion refers to the image of the two lines juxtaposed on the train tracks. The lines converging toward each other remind us of train tracks going into the distance. In other words, a top-down effect causes our brain to impose depth into the two-dimensional image.
Now a phenomenon called "perceptual constancy" comes into play. The retinal cells register the top and bottom line as being precisely the same length because they are the same length. All would be fine if the sensory areas of the brain didn't impose depth onto the image. That causes you, the viewer, to conclude that because the top line is "farther" it must be "bigger." If you could turn off your brain's noisy intrusions of imposing depth onto flat images, you wouldn't be fooled by this illusion.
Perceptual constancy can also explain the moon illusion. The retinal cells tell you that the moon is the same size no matter where it is in the sky. But because your brain's sensory cells are seeing lots of cues at the horizon that suggest distance, they lead you to the faulty judgment that the horizon moon is bigger.
Lost? Try going to this NASA website in which the moon illusion is explained in painstaking detail. There's another explanation of the Ponzo illusion as well, using slightly different terminology.
There are tons of websites showing all sorts of common and not-so-common illusions in our everyday lives. One of the best is Mighty Optical Illusions, a source that updates daily. If you like to travel, you can also enjoy illusions in famous buildings such as the Parthenon. While traveling you can also take pictures that capitalize on our assumptions about depth. For example, for a mere one dollar, a resident expert at the Sphinx in Giza will take a picture of you appearing to be sitting on top of it, kissing it, or holding it ($5 for all 3 poses). Check this posting for another good travel illusion.
Optometrists suggest that visual puzzles, illusions, and games can help protect your vision health. I'm pretty sure that's true. But as important, exercising your brain and your mental flexibility with these visual experiences can give your life a very enjoyable boost.
Follow me on Twitter @swhitbo for daily updates on psychology, health, and aging. Feel free to join my Facebook group, "Fulfillment at Any Age," to discuss today's blog, or to ask further questions about this posting.
Copyright Susan Krauss Whitbourne, Ph.D. 2010
