When I taught in a more traditional classroom setting, I had a mantra that I recited at the beginning of every class: Be Your Own Expert. I wanted students to question received wisdom, to consider the evidence for themselves whenever possible. Every day I told a different story of an “expert” that was later shown to be laughably wrong. It was fun.
My favorite example of “conventional ignorance” masquerading as wisdom is the phrase “the five senses.” People use this expression without ever thinking about it. Once I found a picture book for toddlers called “Your Five Senses.” Indoctrination starts early. I didn’t question it myself until a friend and mentor said something to me about the “other senses.” It got me thinking: “Are there other senses? What might they be?” In very short order I came up with three or four obvious ones, counting ten or eleven within a few days. You can, too.
Go ahead. Bookmark this for a day or two and see how many senses you can come up with. But wait! Read my definition of a sense first: A human sense is a means by which a human mind obtains a unique quality of information about the physical universe. (Not the spiritual, social, or emotional universes, about which humans will reasonably disagree.) Just the physical universe.
OK, here’s your chance to be your own expert. If you keep reading, you’ll kick yourself, because the first few are easy. You may disagree with me about some of them, but verified scientific evidence is on my side. We humans receive at least ten very specific and unique qualities of information about the physical universe.
1 through 5: Hearing, Taste, Touch, Smell, Sight. Some fascinating recent research is revealing amazing insights about these old familiars. For example, there are sensors behind the retina that detect light, but instead of sending the signal to the visual cortex, they are linked to the part of the brain that determines the wake/sleep cycle.
6 - Balance. This sense tells us our orientation to gravity. Balance involves a separate organ, located near each ear (but unrelated to hearing). The three semi-circular canals of the vestibular system run in each of the three dimensions, so we can know our gravitational orientation in three dimensions. Damage to either vestibule causes debilitating vertigo.
7- Temperature. This is NOT the sense of touch, which tells us about pressure and texture. Temperature is a separate quality of information from pressure/texture, and there are separate receptors in the skin for temperature, called thermo-receptors. Actually there are two, one for warmth and a different kind for cold, so arguably this is two separate senses. Heat radiation can be sensed by our skin in the absence of anything to “touch,” eg. in vacuum.
8- Time. While the accuracy of this sense varies greatly (as does smell), most of us will notice if our favorite song is played too fast. . . if I leave the room to use the restroom and come back 2 seconds later, no one would need to consult a clock to know I hadn't been gone long enough. There is clearly a human ability to sense the passage of various quantities of time. Neurologists have not yet described the structure for this function, and it looks as though the “sensor” may be a distributed network of neurons in the brain. Rats can “tell time” even if their entire cortex is removed. Stay tuned.
9- Proprioception, or the kinesthetic sense. Close your eyes and ask yourself where is your left thumb, or your right elbow. No peeking! You'll know, to within an inch or two. You have a 3D map in your head showing the location of each part of your body, no peeking needed. The information comes from cells called proprioceptors (stretch receptors) in all the voluntary muscles of the body. They tell you how stretched or contracted each muscle is, which your brain uses to determine at what angle each joint is held.
10- Interoception, or the body sense. This one provides unique information concerning the geography of your body parts. When you have a headache, you know that the pain is in your head, not your abdomen. When someone touches your shoulder, you know it's your shoulder. This may be related to the geography of nerve endings in the brain, but that's true of every sense.
11-Direction. I accept that this sense is marginal, in that it may be only a combination of balance, time, and/or kinesthetic senses. However, there is some evidence that certain aboriginal peoples have a highly developed sense of direction, that is not eliminated by restricting the other senses. I'm not prepared to say that aboriginal people are other than human, so the sense remains on my list, though tentatively.
For the past fourteen years I have been SO proud of myself for thinking of these on my own. Then along comes Wikipedia (http://en.wikipedia.org/wiki/Sense). Turns out they list even more senses than I do, except they count pain as a separate sense (nociception), along with some fascinating others.
So how many senses do we have? Somewhere between eleven and seventeen. Yet another* example of how we mistake conventional wisdom for actual wisdom.
Be Your Own Expert!
