But in all of this talk, which began a couple of thousand years ago with Aristotle's first tabulations of human senses (he came up with the primary five), there is at least one sense that seems to have been largely overlooked: balance.
That, at least, is the premise of Scott McCredie's book. McCredie declares in his very first sentence that Aristotle erred, and then proceeds to castigate others for not fully appreciating our innate and remarkable ability to move about without toppling over.
McCredie is a Seattle-based writer and this is his first book. These facts do not necessarily put him on the same page with, say, Diane Ackerman, a hugely admired and successful science and nature writer ("A Natural History of the Senses") whom McCredie also takes to task. Still, he makes a good point and a pretty good first effort.
Most of us don't think much about our sense of balance except in its absence. That's not an inconsiderable concern in aging America. After 65, one out of three Americans falls each year, adding up to more than 10 million falls annually, McCredie writes.
"While most falls don't result in serious injury, they are like a game of Russian roulette. Sooner or later the bullet - in the form of fractures, lacerations and sometimes death - will sit in the firing chamber."
But age is only one factor affecting balance, which can be impaired by infections, certain kinds of brain injuries, diabetes and even the dislodging of tiny stones (bits of calcium carbonate crystals) that naturally occur within the inner ear. Yep, we all have rocks in our heads.
After a quick introduction to the biology of balance - otherwise known as the vestibular system - the book devotes chapters to specific conditions: the mysteries of motion sickness (some fish suffer too), spatial disorientation (the likely reason why John F. Kennedy Jr. fatally flew his private plane straight into the ocean on a clear, calm night in 1999) and extreme equilibrium (why some people are tightrope walkers).
Our vestibular systems are crucial to us even before we're born, prompting us to flip to a head-down position in the womb just before birth.
Stimulating one's inner ear - by spinning, for example - may boost brain activity, though too much usually isn't a good thing.
McCredie ends with a short appendix that includes how to evaluate your own sense of balance: Stand on a hard surface and raise one leg about 12 inches off the ground. Count how long you can maintain this position. People between the ages of 20 and 49 average about 24-28 seconds; 50- to 59-year-olds, 21 seconds; 60- to 69-year-olds, 10 seconds; 70- to 79-year-olds, 4 seconds.
To improve, McCredie provides a few exercises. They're fairly easy and, more important, they're good for you. Because as McCredie says, we all need balance in our lives.
- Scott LaFee is a science writer for the Union-Tribune in San Diego.