Your Brain: The Missing Manual

Dizzy Yourself Silly with Optical Illusions on the Web

You've now finished your tour through the oddities of human perception. But the fun doesn't need to end here.

Once upon a time, the only reliable place for average people to see optical illusions was in a somewhat baroque object known as a book. (If you're reading a non-electronic version of this text, you know what I'm talking about.) Books were wildly popular for many years, before becoming replaced by electronic pixels. Today, books are mostly remembered by some of the over-16 crowd as an odd early version of the Internet.

No matter what you think about the march of progress and the colonization of Earth by computers, the Internet has been good for optical illusions. There are dozens of Web sites that show optical illusions in all their glory. Here are some of the best:

• Akiyoshi Illusions. The legendary creator of the rotating snakes illusion (shown on Your Shifty Eyes) also provides pages of hand-crafted illusions. See www.ritsumei.ac.jp/~akitaoka/index-e.html.

• Purves Labs. This top-notch lab studies optical illusions and offers a see-it-yourself section that includes some of the most remarkable color and brightness illusions ever created. See www.purveslab.net.

• Michael Bach's Illusions. Many of the illusions on this Web site are outfitted with multimedia extras, such as little movies that move parts of the optical illusion around so you can verify what you really want to know—that two lines are the same length, two shapes are the same color, and so on. See www.michaelbach.de/ot.

• Wikipedia. The free-for-all online encyclopedia describes a selection of optical illusions, including many of the examples you've seen in this chapter. See http://en.wikipedia.org/wiki/Optical_illusion.

• Mighty Optical Illusions. Although it's a bit noisy—try to use your brain's ignoring power on the Google ads distributed about the top, side, and bottom—this Web site has a solid illusion catalog, and ranges farther afield to get some interesting examples from real life. See www.moillusions.com.

Incidentally, the human race takes advantage of the idiosyncrasies of its visual hardware. Most of us spend hours transforming collections of flickering dots on a screen into an impression of real people. This optical illusion, known as television, is surely one of the most impressive visual ruses ever documented.

The Practical Side of Brain Science: The Power of Expectation

Built-in judgments aren't limited to vision. Our assumptions can blind us to facts and lure us into unwitting conjecture in virtually every way that we perceive the outside world. Advertisers and other nefarious ill-doers rely on these errors. Here are some examples:

• Shocking tastes.If you've ever put a glass to your mouth expecting to drink milk only to taste orange juice, you've felt the power of expectation. There's a moment of palpable shock when the new sensation defies the brain's expectation, and a brief pause before the brain can perceive what it really is.

• Sizes and weights.Many studies show that people confuse size and weight, and let their visual assessment of size influence their impression of weight. One of the simplest ways to see this is by getting several different sized containers (say, a small overnight bag, a suitcase, and a large piece of luggage) and filling them up with materials that weigh the same amount (you can use a pile of heavy books). If you ask someone to judge which is heaviest, they will inevitably pick the smallest one. This is because the smallest one defies the brain expectation that small is light, and thereby makes a bigger impression.

• Food and fecal matter. Can you tell the difference? Apparently not by smell alone. People respond differently to an odor that they sniff out of a test tube depending on whether they're told that it's fancy cheese or human waste.

• Packaging. In many studies, people's reports of how much they enjoy particular foods (and how much they're willing to spend on them) depend on the packaging and brand name as much as the actual food. In his book Blink (Little, Brown, 2005), Malcolm Gladwell describes studies that find people will pay about 10 cents more for ice cream in a pleasingly round container rather than a rectangular one, and will rate the taste of Chef Boyardee products worse if Hector the chef looks like a cartoon character.

All of these examples remind you that perception doesn't lie in the eyes, ears, or any other sense organ—it exists in the brain.