More precisely, the researchers believe that rat neurons process the change in torque over time as a whisker encounters an object, allowing the animal to record the object's exact location.
While the pair hasn't performed behavioral studies on rats to test their hypothesis, they have applied their ideas to build robotic whiskers that mimic the supersensing powers of rats and seals.
In one experiment the researchers connected four steel-wire whiskers to strain gauges, which in turn were tied to a computer.
Brushed repeatedly against a mock human head, the whiskers fed data points into the computer. When connected by smooth curves, the coordinates accurately reproduced the face in three dimensions.
The team also built a similar array of eight plastic whiskers that could detect shifts in air currents, much the same way that seals' whiskers help the marine mammals track the wakes of underwater prey (related photo: the whiskers on a Weddell seal's face).
From Mars to Factories
The researchers say they envision many uses for their new technology, from checking the positions of spare parts on assembly lines to helping robots scour oil pipelines for blockages (related news: "Alaska Oil Pipeline Faces Big Scrutiny After Small Spill" [August 2006]).
Other potential applications could see the whiskers installed on underwater remotely operated vehicles (ROVs) to help the bots operate in dark, muddy, dusty, or high-glare conditions.
"The early part of this work was actually funded by NASA, because they were interested in perhaps putting whiskers on a Mars rover to figure out terrain properties," Hartmann said.
Unlike electromagnetic sensors such as cameras or infrared eyes, whiskers are passive devices that require very little power, an advantage for remote space missions.
Hartmann says that whiskers could also tell a rover when it is stuck or sliding.
"Sometimes if the rover is in sand, for example, the wheels are turning. So the optical encoders on the wheels tell the machine that it's going somewhere, but it's actually not," she said.
By simply feeling the ground, a whisker could tell the rover what's really happening. The same is true for a rover sliding down a hill with its wheels locked.
Noah Cowan, an assistant professor at Johns Hopkins University in Baltimore, Maryland, has helped develop robot antennae inspired by cockroaches.
(Read "Cockroaches Inspire Robot Antenna Design" [April 2005].)
He praised the new work by the Illinois team, writing in an email that "it shows the critical role of mechanics in decoding sensory signals, which is something that neuroscientists often neglect."
He adds that building tactile probes like the robotic whiskers is a "great idea," but notes that Mother Nature offers other design inspirations, too.
Real insect antennae "have thousands of sensors for touch, smell, temperature, and pressure all along the mechanical probe itself, not just at the base" like whiskers do, he said.
The feature, he says, may be one of the reasons insects are so abundant and widespread.
"Find a bug without a pair antennae—it is not easy," he said.
Meanwhile, study co-author Hartmann says that her research has important implications for neuroscience as well.
"There are probably 500 papers published every year on the rat whisker system," which, she said, serves as a model for how animals process and transmit information from outside their bodies to the highest levels of the brain.
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