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University of Pittsburgh researchers call it "the cave" -- and for good reason. It's dark, a little scary, and visitors must wear safety harnesses and hard hats.

But the cave at the Medical Virtual Reality Center at Pitt's Eye and Ear Institute in Oakland doesn't provide a run-of-the-mill spelunking experience.

It's part of a computer laboratory where researchers hope to answer questions about why certain visual environments cause people to lose their balance.

The centerpiece is the cave, officially called the BNAVE, for Balance Near Automatic Virtual Environment.

It is a virtual reality display room large enough for people to immerse themselves in a computer-generated visual environment such as a grocery store or the top of a skyscraper.

"We're bringing the real world into a setting where we can control the stimuli to figure out how best to treat people with dizziness and balance problems," said Patrick Sparto, the center's faculty director and an assistant professor of physical therapy, otolaryngology and bioengineering.

The body relies on information from three systems to maintain balance -- the vestibular system in the inner ear, vision and somatosensation, which is the feeling of where the joints are in space and the sensation of pressure on the skin.

"If the brain gets information from all three systems that makes sense, it has no problem," Sparto said. "But if there is conflicting information or a disruption in the brain, then it can lead to balance difficulties."

Balance problems are caused by conditions such as inner ear infections, vertigo, stroke, brain injury, migraine headaches and Meniere's disease, which causes acute attacks of vertigo. Symptoms can include severe dizziness, nausea, blurred vision and disequilibrium.

Balance problems also can result in falls, which are the leading cause of death by injury and the most common cause of nonfatal injuries among the elderly, according to the National Center for Injury Prevention and Control. In 2001, more than 1.6 million seniors were treated in emergency rooms for fall-related injuries.

It's difficult to determine what causes people to fall because of the complex sensory input and body systems interactions involved, Sparto said. It's also hard to develop ways to treat people with balance disorders in a setting that replicates real-world situations.

That's why Pitt researchers collaborated with computer experts from the Georgia Institute of Technology to develop the BNAVE.

Virtual reality allows researchers to simulate the real world in a controlled environment.

The nearly $200,000 project was conceived about five years ago and is paid for with grants from the Eye and Ear Foundation and the National Institutes of Health.

Here's how the BNAVE works: Patients step on to a scale-like platform at the entrance to "the cave," which is an enclosed wooden frame draped in black curtains.

Projected seamlessly on three vertical screens and a floor screen is a geometric, black-and-white virtual image that surrounds the horizontal field of view and resembles a checkerboard with a giant bull's-eye in the center.

Researchers can adjust the image's width, length, brightness and complexity using personal computers.

Secured with a harness, patients are asked to look straight ahead and stand as steady as they can as the visual scene starts to move forward. The platform measures the forces underneath the patients' feet as they sway back and forth in response to the moving image. A helmet equipped with miniature video cameras tracks their eye movements.

Within the next year, doctors and physical therapists hope to use the BNAVE as a rehabilitation tool for patients with balance disorders.

People with balance problems usually are treated through a process called adaptation, in which patients learn to reweight the signals coming from their eyes, body and mind to account for any sensory mismatch. The idea is to expose patients slowly to various stimuli to recalibrate their balance systems.

Virtual reality provides a physically and psychologically safe environment for this type of therapy, said Dr. Mark Redfern, the center's co-director and a professor of bioengineering and otolaryngology at Pitt. It also allows doctors to make quantifiable, instant changes to tailor the therapy program to patients' progress, Redfern said.

"This is a high-tech tool to help people learn how to pay attention to the right signals from their major sensory systems," Redfern said.

For example, besides the abstract checkerboard setting, computer programmers designed a virtual reality grocery store for the BNAVE. Pitt researchers can change just about every imaginable variable in this "Grocery World," including the heights of the shelves, the number of food items, the floor tile pattern and the brightness of the overhead lights. For now, "shoppers" move through the store using a joystick, although computer programmers are developing a treadmill that will give the illusion of walking while pushing a cart.

"People with balance or dizziness problems often tell us that they have increased symptoms when they go into a grocery store," Sparto said. "Ideally we'd take them out to the store for rehab, but that isn't safe or practical so this is the next best thing."

Jeffrey Hohn, 53, of Bentleyville, Washington County, suffers from balance problems because of inner ear injuries caused by a coal mining accident last year. Despite extensive therapy, Hohn still has problems in grocery stores because the layout of supermarket aisles, with stacks of products on both sides, creates a strong sense of movement.

"It's awful," Hohn said. "If I walk into a Wal-Mart and stand in the aisles and the place is packed, I just have to get out. I start getting very disoriented and eventually my system will shut down. I go into a dazed-like state."

The BNAVE could one day soon be able to help Hohn and others with balance disorders by teaching them to perform typical eye and head movements as they go through the essential activities of daily living in a complex visual environment, Sparto said.

It also could be used to help people overcome a fear of heights and other panic disorders, he said.

The size and cost of the BNAVE mean it isn't likely to turn up soon in every hospital or physical therapy clinic, Redfern said. But information learned from the BNAVE could one day be incorporated into portable headsets for virtual reality systems.

"Technology is changing all the time," Redfern said. "We are looking into smaller, more affordable solutions that could be used on a more widespread basis. For right now, though, we are on the leading edge."

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