Issue 15.04 – March 2007
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Mixed FeelingsSee with your tongue. Navigate with your skin. Fly by the seat of your pants (literally). How researchers can tap the plasticity of the brain to hack our 5 senses — and build a few new ones.By Sunny BainsPage 1 of 3 next »
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.
Rants + Raves
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“It was slightly strange at first,” Wächter says, “though on the bike, it was great.” He started to become more aware of the peregrinations he had to make while trying to reach a destination. “I finally understood just how much roads actually wind,” he says. He learned to deal with the stares he got in the library, his belt humming like a distant chain saw. Deep into the experiment, Wächter says, “I suddenly realized that my perception had shifted. I had some kind of internal map of the city in my head. I could always find my way home. Eventually, I felt I couldn’t get lost, even in a completely new place.”
The effects of the “feelSpace belt” — as its inventor, Osnabrück cognitive scientist Peter König, dubbed the device — became even more profound over time. König says while he wore it he was “intuitively aware of the direction of my home or my office. I’d be waiting in line in the cafeteria and spontaneously think: I live over there.” On a visit to Hamburg, about 100 miles away, he noticed that he was conscious of the direction of his hometown. Wächter felt the vibration in his dreams, moving around his waist, just like when he was awake.
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.
So here’s the solution: Figure out how to change the sensory data you want — the electromagnetic fields, the ultrasound, the infrared — into something that the human brain is already wired to accept, like touch or sight. The brain, it turns out, is dramatically more flexible than anyone previously thought, as if we had unused sensory ports just waiting for the right plug-ins. Now it’s time to build them.
How do we sense the world around us? It seems like a simple question. Eyes collect photons of certain wavelengths, transduce them into electrical signals, and send them to the brain. Ears do the same thing with vibrations in the air — sound waves. Touch receptors pick up pressure, heat, cold, pain. Smell: chemicals contacting receptors inside the nose. Taste: buds of cells on the tongue.
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.
When computers sense the world, they do it in largely the same way we do. They have some kind of peripheral sensor, built to pick up radiation, let’s say, or sound, or chemicals. The sensor is connected to a transducer that can change analog data about the world into electrons, bits, a digital form that computers can understand — like recording live music onto a CD. The transducer then pipes the converted data into the computer.
But before all that happens, programmers and engineers make decisions about what data is important and what isn’t. They know the bandwidth and the data rate the transducer and computer are capable of, and they constrain the sensor to provide only the most relevant information. The computer can “see” only what it’s been told to look for.
The brain, by contrast, has to integrate all kinds of information from all five and a half senses all the time, and then generate a complete picture of the world. So it’s constantly making decisions about what to pay attention to, what to generalize or approximate, and what to ignore. In other words, it’s flexible.
In February, for example, a team of German researchers confirmed that the auditory cortex of macaques can process visual information. Similarly, our visual cortex can accommodate all sorts of altered data. More than 50 years ago, Austrian researcher Ivo Kohler gave people goggles that severely distorted their vision: The lenses turned the world upside down. After several weeks, subjects adjusted — their vision was still tweaked, but their brains were processing the images so they’d appear normal. In fact, when people took the glasses off at the end of the trial, everything seemed to move and distort in the opposite way.
Later, in the ’60s and ’70s, Harvard neuro biologists David Hubel and Torsten Wiesel figured out that visual input at a certain critical age helps animals develop a functioning visual cortex (the pair shared a 1981 Nobel Prize for their work). But it wasn’t until the late ’90s that researchers realized the adult brain was just as changeable, that it could redeploy neurons by forming new synapses, remapping itself. That property is called neuroplasticity.
This is really good news for people building sensory prosthetics, because it means that the brain can change how it interprets information from a particular sense, or take information from one sense and interpret it with another. In other words, you can use whatever sensor you want, as long as you convert the data it collects into a form the human brain can absorb.
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