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Ever since seeing the satellite imagery from NASA’s Jet Propulsion Laboratory, John Hollerbach wants people to walk on Mars. If his virtual reality project reaches fruition, as he claims it will, the Martian sand dunes may open to the public in just a few years.

Hollerbach is one of the lead researchers working on the University of Utah’s Treadport, a virtual reality system that uses a technology called “locomotion interface”where users experience the pull of gravity and the resistance of inclines while navigating within a virtual worldto make the simulation far more lifelike. Hollerbach and his team, in conjunction with researchers at the University of Minnesota, Vanderbilt University, and Mount Holyoke College, are in the first year of a five-year, four-million-dollar grant from the National Science Foundation to develop the Treadport. Aside from two laboratories in Japan, they are the only group exploring the potential of locomotion interface. And while the technologyin particular the graphicsis still at a fairly early stage, Hollerbach believes that within five years they should have a commercially viable product that can be used for military simulations, education and even recreation.

Virtual reality chamberscommonly called cavesare nothing new. They’ve been around since the early 90s, and today there are dozens of them in the U.S., most at universities (see “The Virtual Voyager). Typically, a user steps inside an eight-foot chamber, surrounded on all sides (sometimes including floor and ceiling) by video screens. Wearing 3-D glasses and gripping a joystick, the user navigates through a virtual world, such as the interior of a blood vessel or pre-Vesuvian Pompeii. But moving around with a joystick hardly mimics realitynor does banging into a laboratory wall while strolling across a virtual open field. Also, because movement through the virtual world is not directly correlated with the user’s body movement, it’s easy for someone to lose track of their navigational path, essentially getting “lost” in the virtual world. And that’s where locomotion interface comes in.

The Treadport that Hollerbach and his team are developing is a virtual reality cave in which the user controls the flow of imagery by moving on a treadmill. “There’s a physical cost to moving,” says Hollerbach. “The ability to walk or run makes the whole thing far more natural.”

The key is a tether that attaches to the user’s lower back and feeds information about the user’s body language into the hardware controlling the system. The tether locates and measures the user’s position, and based upon those measurements controls both the visual display and the velocity of the belt. “Essentially,” Hollerbach says, “the tether turns the user’s entire body into a joystick.” But it also adds an extra dose of reality: gravity. So, if you’re climbing a staircase inside a pyramid somewhere in Mesoamerica, the tether applies an inertial force based on the gradation of the slope. And if you look down to admire the stellar virtual rendition of the stone floor and accidentally bang into a wall, the tether jerks you to an all-too-real halt.

But there’s still much to be done before the Treadport can bring Mars to the people. In addition to Hollerbach’s still-pending application to use NASA’s Mars photos, the real bottleneck in virtual reality interfaces is in actually building the virtual worldboth constructing the graphics and understanding the psychology of navigation and way-finding. According to John Reisser, a cognitive scientist at Vanderbilt who’s working with the Treadport visual graphics team, “We’re still working on trying to increase the ease of spatial learning and perception when exploring virtual worlds.”

Meanwhile Hollerbach, unable to keep himself from lapsing into Star Trek imagery, confesses that “what we’re really trying to do is to create a holodek of sorts.” He sees no end to the possible applications: training firefighters, previewing architectural designs, rehabilitating patients, or immersing students in historyancient Romeor biologyas an ant walking through its colony. And as for the red planet, he says, “We can use the tether to reduce the gravity load so you can walk as you actually would on the Mars surface.”

As for which application gets there first, the entomologists and trekkies may just have to duke it out.

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