The treatment usually starts with a digital scene and no violence. But in subsequent sessions, the therapists -- after giving warning -- heighten the intensity and specifics of the re-created event. They can make the platform shake more violently. They can set off simulated explosions and gunfire and add fog, smoke and night-vision effects, along with the smells of body odor and Iraqi spices.
"Habituation occurs when they repeat their story over and over again," Perlman said. "They start to learn they can tolerate their distress, they can work through it."
If all of that proves to be too much, the session can be interrupted for a discussion or be made less vivid.
Researchers say they want to ensure the experience feels real enough to trigger emotions without being overly bloody. Though some patients have temporarily removed the goggles or asked for a break, no one has completely freaked out, according to McLay. "We are prepared for that experience," he said. "The great thing about virtual reality is that you can turn it off."
Citing privacy issues, authorities did not allow interviews with patients. But a reporter was permitted to talk to a Navy medic who recently served in Iraq and who, though not a PTSD patient, tried one system.
"It's pretty real. The vibration and the sights and sounds and everything were pretty darn close. I was waiting for shrapnel overhead," said Eugene Gochicoa, a Navy corpsman 1st class. "It did kind of take me back to when I was back there ... except I knew I was safe here."
FOR a reporter, a test run at USC's lab had a disorienting double effect: the fun of being inside an astonishingly lively video game but also the dread of being trapped in a dangerous situation that other people controlled. The scenarios were changed to give me a sampling: I drove a Humvee through a smoky field until insurgents' bullets cracked the windshield. I had a growing sense of paranoia. I heard my own footsteps as I walked quickly down a street past suspicious characters.
Hearing prayer calls, I entered a beautifully decorated mosque, where I suddenly encountered a gunman. Again, the story line switched and I heard and felt helicopters nearby. I ran past burning cars and a wounded man holding his head. Am I the next to be shot?
Engineers want to make systems more portable. And redesigns may make the simulated urban streets messier and add smells -- such as roasting lamb.
One of the systems grew out of the computerized war training program known as Full Spectrum Command, which was designed, with Army funding, at USC's Institute for Creative Technologies. The institute also produces Hollywood special effects and multimedia systems for healthcare and education.
The Army software later was adapted for the popular Full Spectrum Warrior video game and then morphed again, in collaboration with Virtually Better Inc. in Georgia, for the therapy. "From training to toy to treatment" is the way the sequence was described by USC professor Albert "Skip" Rizzo, one of its adapters, along with computer engineer Jarrell Pair.
Rizzo, a psychologist who works in gerontology and directs the institute's virtual-reality psychology lab, previously used other VR programs to aid Alzheimer's and brain-injury patients and youngsters with attention deficits. VR, as it is often called, is being tried around the country for addictions and phobias, such as fear of flying. Weill Cornell Medical College in New York is testing a version for people who witnessed or responded to the terrorist attacks on the World Trade Center in 2001.
Because there are no clear battle lines and it is difficult to identify enemies, the Iraq war is a petri dish for the constant stress that can produce PTSD, Rizzo said.
"We are sending teenagers 19 years old to fight wars, and we owe them whatever can be done, using the latest technology, to look after those people after the fact," he said.
The federal government has a financial, as well as humanitarian, interest in trying to speed treatment and reduce long-term disability payments. But even if some otherwise healthy malingerers use the technology to bolster phony trauma claims, Rizzo said, he can live with that "as long as I know that the people who really need the treatment are getting it."
A more primitive virtual-reality therapy -- depicting a jungle and Vietnam-era helicopters -- produced some significant improvement for Vietnam War veterans, researchers at the VA Medical Center in Atlanta reported in 2001. According to study leader Barbara Rothbaum, director of Emory University's trauma and anxiety recovery program, the experience was so effective that some of those veterans said they saw tanks and Viet Cong, even though none were presented on-screen.
Patients, she said, "will fill in with their own memories."