Big World, Little Brain

Art by Paul Kim. Copyright Rebecca Schwarzlose

How does your brain—an organ smaller than a soccer ball—represent the big, wide world of sensations, events, and meaning unfolding all around you? 

Your experience of the world feels so seamless and boundless that you may never have thought to ask this question. But once asked, the question demands an answer. Or, in this case, it demands three answers. Because it is only thanks to three solutions that you can perceive your world at all. And it is these solutions, in turn, that determine exactly how you experience your world.

You Miss More Than You Think

The first and simplest solution is that your brain doesn’t represent everything taking place around you. Not even close. You perceive only a small fraction of the energy and information buzzing all around you.

Much of that buzzing information goes unseen and unfelt because your body lacks the capacity to detect it. Whereas birds can see ultraviolet light, snakes can see infrared light, insects can see the polarization of light, mice can hear ultrasonic frequencies, and electric fishes can detect faint electric signals with their skin, you can do none of these things because your eyes, skin, and ears lack the cellular machinery that would allow you to detect them.

Although having infrared vision would be a great party trick for you or me, it is vital for snakes that need to hunt their prey in the dark. Every creature’s body is mostly blind and insensate, only detecting those faint signals from the environment that it needs to survive.

But being mostly blind to the goings-on around you is only part of the solution. That’s because you can only comprehend the thrum of information you do receive from your eyes, skin, ears, nose, and tongue if it is processed by your brain. This processing depends on the activity of brain cells called neurons and the connections between them. Brains with more of these interconnected neurons can process more information, but they are also heavier and require more energy. As a result, perceiving any feature of one’s world comes with steep costs: a larger, heavier head to house one’s brain and a larger appetite to sustain it.

Your Brain Is Full of Maps

This brings us to the second grand solution that makes perception possible. Creatures on earth, including humans, eke more abilities out of their brains by organizing neurons into literal maps. These maps allow creatures to pack more neurons into a brain while keeping the costly connections between them as short as possible.

Your different brain maps represent different features of your world: information about light detected with your eyes, information about sound detected with the cochleae in your ears, pressure detected with your skin, locations in space around your body, and so much more. Thanks to maps, your brain can house five senses rather than just one or two, all while keeping your hat size small and your appetite manageable. 

Yet brain maps alone cannot solve the problem of perceiving a big world with one measly brain. There is still too much detailed information reverberating in the world around us and only so much energy and headspace to go around. As a result, your brain maps cannot faithfully represent all the information striking the surfaces of your skin, the backs of your eyeballs, and the deep recesses of your ears.

Your Maps and Your Perceptions Are Warped

This brings us to the third grand solution: Your brain maps are warped, preserving some details while sacrificing others

Much like Manhattan real estate, territory in the brain is both finite and expensive. Brains evolve and develop to make the most of that modest terrain. Your brain maps are distorted to save energy and space. And these distortions, in turn, distort how you perceive your world.

Consider your sense of sight. You can see far more detail at your center of gaze, or where you are looking at any given moment, than “out of the corner of your eye.” For an illustration, just try reading these words without looking right at them.

Ideally, you would be able to see things equally well out of the corner of your eye as you do at your center of gaze. But you need more neurons, and more connections between those neurons, to represent fine details. In order to see equally well in your visual periphery as you do at your center of gaze, the visual maps in your brain would have to be thirteen times larger. If this change sounds innocuous, think again. It would make your visual brain maps alone too large to fit inside your skull. And that would leave no room for the brain maps you rely upon to hear, feel, and move.

To avoid such catastrophic outcomes, brain maps devote most of their estates to representing detailed information from “sweet spots” for perception, at the expense of practically everything else. 

When it comes to touch, your sweet spots are your fingertips. You can measure your ability to detect fine detail by asking someone to apply two points of pressure against your skin and testing how far apart they need to be for you to detect that they are two points rather than one. With your index finger, you can distinguish between two pressures a mere millimeter apart—a true feat of detailed tactile perception. That distance must be about seventy times greater—roughly the width of a woman’s hand—for you to distinguish between them on your back.

Oddly enough, your ability to perceive crucially depends on all that you don’t perceive. Thanks to our limited senses and distorted brain maps, you can experience and interact with your world… and do it all with a brain that’s smaller than a breadbox.

This post first appeared on Psychology Today

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