Struggling with your bags, you exit the grocery store while grasping your change. At the newspaper vending machine, as you glance over the headlines, you separate out the correct coins, depositing them, then opening the machine, extracting your paper, and balancing it among your bags. You adjust the corner of the frozen pizza box scraping your arm. Pausing to fish through the contents of your pocket, discarding the matchbook and forgotten frozen pizza coupons, you extract your keys.

With your groceries resting on the car's roof, you unlock the trunk, experiencing back stiffness as you load it. Shutting the trunk and moving toward the driver's door, you shiver at the chill and rain. At home you enjoy your hot pizza, give the TV remote a workout, and fall into your soft warm bed, ending your day the way you spent it, oblivious to the amazing internal environments. The pressure of the pizza box, the ache in you back, and the goose bumps you got from the cold rain all resulted from your passive touch sensors at work.

Active touch let you insert coins in the newspaper machine, pull your keys from the items your pocket, open your car, and use the television remote. Active touch provides your most immediate connection to your surroundings. You can locate objects through sight, and, to a lesser extent, hearing and smell, but only touch absorbs information on their material aspects – texture, rigidity, weight, and temperature.

As a baby you discovered your mouth, and started putting things into it, but you weren't hungry; you had learned that your tongue was full of touch receptors, and were feeling your way around the nursery. Each part of your body has similar receptors.

Joint receptors allowed you, without looking, to find your keys, steer your car, and operate your remote, by constantly tracking the location of your limbs.

Just beneath your skin, including that of the soles of your feet, are receptors reacting with your environment. When you crossed the parking lot, they tracked changes in its surface, so that you automatically adjusted your balance as you went.

And even when you are not consciously aware of touching anything, untold millions of sensors feed findings to the parietal cortex of your brain, where, like an infinitely intricate jigsaw puzzle, they are re-assembled into an image of your physical reality – your "body image". Telling you at a glance if you can squeeze into the space at the end of the church pew, or reach the items on the top shelf of Aisle 9, it defines your place in the physical world.

Is the ability to picture one's own body important? In 1965, former U.S. Senator Bill Bradley, as an undergraduate basketball phenomenon at Princeton, was the subject of a John McPhee biography; McPhee wrote of an on-court interview during which Bradley, with his back to the basketball hoop, sank two over-the-shoulder shots.

Bradley told McPhee, "When you have played basketball for a while, you don't need to look at the basket when you are in close like this. You develop a sense of where you are." That "sense of where you are" – knowledge of where you end, and everything else begins, enabling you to function in the world – is the crowning achievement among all the amazing achievements of your sense of touch.

Jason Ladock

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