Your Brain: The Missing Manual

Chapter 4. Perception

Your brain is a reality-construction machine. It takes the vast oceans of information that flood your senses, and transforms them into a highly subjective inner world.

This inner world has a few things in common with outside reality, but less than you'd think. It's run by a processing system that's quick to jump to conclusions, confidently ignorant of its mistakes, and easily fooled. This processing system sees what it expects to see, hears what it expects to hear, and petulantly refuses to be corrected on even the simplest point. You may enjoy this world or you may not. However, you'll never get a chance to step out of your head and take a clear look at what's really happening outside.

That's where this chapter fits in. Here, you'll explore some of the ways that the brain shapes outside reality. You'll learn about the quirks of the eyes, ears, and other senses, and the automatic assumptions that are deeply ingrained in your brain. Occasionally, this knowledge will help you "unfool" yourself—in other words, it lets you anticipate your brain's hiccups and work around them. Other times you'll learn enough to fool someone else, which is just as good (and makes a solid foundation for a career in politics, advertising, or real estate). Either way, this chapter gives you an opportunity to pull back the curtain and steal another quick look at the strange machine that runs your life.

The Doors of Perception

It's tempting to divide the brain's information processing into two neat categories: conscious (what you know you see and hear) and subconscious (what your brain deals with automatically, behind the scenes). After all, you don't consciously perceive the inner ear signals that ensure you stay balanced while navigating an intricate dance routine, but you are acutely aware of the crushing heel that your dance partner just placed on your big toe.

However, if you dig a little deeper into the brain's jelly-like matter you'll quickly find that it's a little bit like sharing an apartment with a group of freewheeling friends—there's a lot more going on than you realize (and a fair bit more than you'd probably consent to). Basic avenues of perception that you take for granted, like seeing, hearing, and touch, are actually colored by layers and layers of the brain's automatic preprocessing. In essence, your brain expects the world to behave in certain ways, and it subtly shapes your perception according to these biases.

Furthermore, this isn't just a story about any one sense. It most obviously affects vision, but its effects are equally apparent with sound, touch, taste, and more complex combinations. These automatic assumptions happen at the lower levels of the brain (for example, through specialized neurons that deal with particular optical phenomena) and higher ones (for example, in the folds of the cerebral cortex, where deep thinking takes place).

Although this automatic processing sounds a bit suspicious, you'd be ill advised to turn it off (and short of heavy quantities of illegal pharmaceuticals, there's no way you could). Most people don't want to spend minutes thinking about shapes, illuminations, and perspective simply to follow their favorite sitcom. Similarly, they don't want to go through a painstaking process of logical deduction to determine if the object they're looking at is a person and, furthermore, if it is in fact their spouse (as memorably described in Oliver Sacks' The Man Who Mistook his Wife for a Hat [Summit Books, 1985]).

That's not to say it isn't worthwhile to learn more about the automatic processing of your brain. Using the insight you pick up in this chapter, you'll be able to:

• Defend yourself against accidental mistakes. A little bit of knowledge can help make certain that you aren't tripped up by faulty brain assumptions (or at least figure out what went wrong after the fact). This is a theme you'll revisit throughout this book, including the next chapter, when you'll discover the ways the brain can mangle memories despite the best intentions of the rememberer.

• Defend yourself against out-and-out trickery. Magicians, pickpockets, and psychics often rely on the well known quirks of human perception—the assumptions, omissions, and unusual glitches the brain encounters while processing the outside world. Once you know what to expect, you'll be able to unravel a few tricks (or get better at pulling them off yourself).

• Dazzle your friends with party tricks. What über-geek doesn't need a trusty optical illusion to break the ice at a party? And if your interests are more practical, wagering possibilities abound ("Are you willing to bet this line is longer than that one?").

Late Night Deep Thoughts: Can We Know Reality?

We often feel that our senses "wire" us into the outside world. They can be a bit dodgy at times, but surely they're based on objective reality—that is, the sounds and sights that are actually unfolding around us.

This comfortable assumption doesn't account for the many ways that human biology shapes the world we perceive. The most obvious example is the way we perceive colors. Due to the architecture of the human eye (which contains three types of color-sensing cells), the continuous spectrum of light is split into arbitrary regions that have dramatically different meanings to painters, drag queens, and interior decorators. The rather embarrassing truth is that there's no qualitative difference between red wavelengths of light and blue wavelengths of light—they're simply different parts of a smooth, continuous spectrum of light. You could make just as strong a case for breaking the spectrum into 12 primary colors as three. It's somewhat like calling some water green and other water yellow based on its temperature.

In fact, there's no reason why human beings couldn't have crossed the millennia of evolution with dramatically different optical hardware—for example, eyes that divide light into two dozen colors or eyes that can tune into parts of the light spectrum we normally can't discern. All this suggests that our senses give us a projection of the external world—one that filters most of it out and shapes the rest in more meaningful (to us) human terms.

And color is only the beginning of the trouble. A similar problem exists with our hearing, which translates something purely mechanical—vibrations of air molecules—into speech, music, and irritating late-night car alarms. The next time you're listing to a dull sermon from your boss, remind yourself that sound is essentially a "made-up" phenomenon. There's no reason that human beings couldn't sport some other type of organ to transform a limited band of input (say, underarm tickles) into a completely different way of perceiving the world. After all, our world is filled with stimuli we can't perceive—infrared (heat) radiation, ultraviolet light, electromagnetic fields, you name it. For the most part, we aren't tuned into these details because they don't give a competitive advantage to life on Earth. However, they're no less fundamental a reflection of reality than the narrow sliver we do perceive.