The ancient Greek philosopher Aristotle said that human beings experience the world through five channels. We call these our senses of sight, hearing, smell, taste and touch.

Balance, the ability that enables humans and other animals to stand on our feet and move about without falling, depends on three senses … of which only one – sight – appears on Aristotle’s list. The other two – the proprioceptive and vestibullar senses – didn’t make the great philosopher’s list because, unlike eyes and noses and tongues and skin, the organs that mediate these senses cannot be seen from the outside. Aristotle drew his conclusions by watching live people, not by dissecting cadavers. Perhaps that’s why he “missed” the proprioceptive and vestibullar senses.

The Proprioceptive Sense

Like radar in a busy airport tower, by which air traffic controllers track the positions of aircraft, proprioception allows us to keep track of our heads, fingertips, toes and everything in between at every moment. The word “proprioception” derives from the Latin word from which we get “appropriate,” in the sense of ownership. Proprioception is the sense whereby we own our bodies, and thereby control our motions.

The organ of proprioception consists of hundreds of millions of sensors distributed throughout our bodies. These sensors relay data about the tension of our muscles, angles of our joints, pressure on the soles of our feet when we are standing, and even attitudes of individual hairs. These fibers converge in the cerebellum, the structure at the lower rear of the brain. The cerebellum processes the information delivered by these fibers and coordinates our motions. It does its work below the threshold of consciousness, enabling us to move without thought during emergencies.

(Proprioception also sparks the beginning of our sense of self: As infants develop, they soon discover that some objects can only be seen, heard, smelled, tasted or touched, while other objects (their own bodies) can also be felt from within. The latter objects eventually become “me,” while everything else becomes “not me.” We are on our way to building a separate identity.)

The Vestibullar Sense

The organ of equilibrium, also called the vestibullar system, consists of interconnected canals (the labyrinth) that lie hidden within our inner ears. Millions of hairs lining the labyrinth detect changes in motion and convey this information to the cerebellum.

Our sense of equilibrium tells us whether we are moving or at rest. This sense also gives is information about “up” and “down.” We are most aware of this sense when we become nauseas or dizzy.

Individuals whose vestibullar systems are compromised feel that they are falling, even when lying in bed.

The Sense of Sight

Our eyes receive information from and about the world around us (when light is available), and transmit that data to the brain, which organizes it into images. The brain “stitches” these images together, thereby creating “maps” of the world that allow us to successfully avoid obstacles and get where we are going. (People who are blind, by the way, create “sound maps” that are every bit as reliable as the “visual maps” that sighted people create.)

Balance

We achieve balance as our senses of equilibrium (by which we know up from down), proprioception (by which we know where our body parts are) and sight (whereby we know where things are) contribute data to the cerebellum, which in turn orchestrates our movements. We experience balance as dynamic, moment by moment state that is best handled below the threshold of consciousness. In other words, we keep our balance more easily if we don’t think about it.