Making Sense of the World

I just learned there are actually 6 senses, rather than 5.

There's a reasonably well-accepted sixth sense (or fifth and a half, at least) called proprioception. A network of nerves, in conjunction with the inner ear, tells the brain where the body and all its parts are and how they're oriented. This is how you know when you're upside down, or how you can tell the car you're riding in is turning, even with your eyes closed.

It's part of a recent Wired article (available on line) that explores different ways of enhancing the senses that people have. The implications for those who want to treat disabilities or those who simply want to enhance the human mind and body are fascinating.

For six weird weeks in the fall of 2004, Udo Wächter had an unerring sense of direction. Every morning after he got out of the shower, Wächter, a sysadmin at the University of Osnabrück in Germany, put on a wide beige belt lined with 13 vibrating pads — the same weight-and-gear modules that make a cell phone judder. On the outside of the belt were a power supply and a sensor that detected Earth's magnetic field. Whichever buzzer was pointing north would go off. Constantly.

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Direction isn't something humans can detect innately. Some birds can, of course, and for them it's no less important than taste or smell are for us. In fact, lots of animals have cool, "extra" senses. Sunfish see polarized light. Loggerhead turtles feel Earth's magnetic field. Bonnethead sharks detect subtle changes (less than a nanovolt) in small electrical fields. And other critters have heightened versions of familiar senses — bats hear frequencies outside our auditory range, and some insects see ultraviolet light.

We humans get just the five. But why? Can our senses be modified? Expanded? Given the right prosthetics, could we feel electromagnetic fields or hear ultrasound? The answers to these questions, according to researchers at a handful of labs around the world, appear to be yes.

It turns out that the tricky bit isn't the sensing. The world is full of gadgets that detect things humans cannot. The hard part is processing the input. Neuroscientists don't know enough about how the brain interprets data. The science of plugging things directly into the brain — artificial retinas or cochlear implants — remains primitive.

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