Joshua Frey occasionally hears the voice of his best friend -- a fellow Marine who was killed in Iraq in 2004.
It's one of his many symptoms brought on by post-traumatic stress disorder, or PTSD, that Frey is trying to overcome using a new virtual reality therapy for troops returning from Iraq. The three-year, $4 million experiment is being run by the Pentagon's Office of Naval Research.
A July 2004 study published in The New England Journal of Medicine reported that about 17 percent of troops returning from Iraq suffer from PTSD-related symptoms.
The 28-year-old Frey agreed to take part in the treatment after flashbacks and nightmares replayed the horrors of war so frequently that he had difficulty functioning once he got home.
He says feelings of anxiety, guilt, and depression are often overwhelming and take a toll on his marriage. And pain from a shoulder wound brings back memories of the day Frey was shot during a firefight, while trying to help rescue his best friend, Joshua Dickenson.
"It's so hard for me because I have so much stuff going on in my head and I break down and I cry, and I just get emotional and I just don't know what to do sometimes," he said.
So once a week, Frey has agreed to meet with Dr. James Spira at the Naval Medical Center in San Diego for therapy sessions. But instead of just talking about his experiences in Iraq, Frey puts on special goggles to relive them inside of a realistic videogame-like simulation that re-creates the sights, sounds -- and soon -- the smells of the battlefield. It's called exposure therapy.
Inside the virtual world, Frey sees a generic Middle Eastern desert city that could easily double for Baghdad. It is quiet at first. Sensors attached to his fingers and body display heart rate, breathing and other information on a monitor for Spira to see how his patient is responding.
When he's sure Frey is doing all right, Spira begins clicking his mouse to gradually add ambient noises like distant gunshots and jets flying overhead. Frey's breathing becomes shallow. His heart rate increases. Next, he begins to hear accented voices shouting at him, saying things like "Go home cowboy!" The sounds of explosions and machine guns get louder as a Blackhawk helicopter swoops in for a landing in the middle of the street.
"This isn't real," Spira reassures Frey. "Just reminders from the past. You can let those thoughts be further away, more distant. They will still come, but you don't have to pay attention to them. You can say to yourself, 'these are just memories.' "
The virtual reality world, Spira said, "triggers those thoughts, those feelings, those earlier reactions they had. What we're trying to do now is train them to have different reactions to those same stimulus and reminders."
For Frey, who served with the 3rd Marines 1st Battalion, the thoughts and feelings are still vivid. He says he was always on edge in Iraq from the constant threat of mortar attacks, roadside bombs and sniper fire.
"There never was a really secure place," he said, thinking it couldn't get much worse.
Then came Dec. 12, 2004.
Frey says the morning had been relatively quiet when a gunbattle suddenly broke out between insurgents and Marines in the city of Fallujah. Dickenson was shot in the head during the firefight and died. Frey, responding to a call of a man down, was hit a few minutes later.
The bullet ripped through Frey's right shoulder, shattering the bones in his arm and causing major nerve damage.
But when he got home, he found his mental wounds were at least as debilitating as the physical ones. He hopes the virtual reality treatments will help him get his life back on track.
"It gets me to control my breathing," Frey said. "I just stay in the moment and know I'm not over there."
Frey is experiencing a digital landscape developed by Dr. Skip Rizzo and his team at the University of Southern California's Institute for Creative Technologies. Rizzo and his colleagues created the simulation by recycling the virtual world designed for the combat video game "Full Spectrum Warrior."
A psychologist, Rizzo believes virtual reality therapy is so effective because it forces patients to recall painful memories rather than avoid them.
In traditional talk therapy, Rizzo said, "you're asking somebody who's been traumatized by an environment to imagine it in the great detail needed to produce a therapeutic effect. With virtual reality, we know what the person is seeing."
"Sound is very important for emotion," according to Rizzo. "The sound of a bullet flying by can raise someone's arousal level in a way that maybe a visual might not."
Future upgrades will include smells like gasoline, burning rubber and gunpowder -- important because smell is so tightly linked to memory and emotion.
Rizzo and other psychologists hope the video game pedigree of their simulation will appeal to a digital generation, breaking the stigma of getting help.
"Soldiers don't want to appear weak," said Rizzo. "To admit you have PTSD may be perceived by others -- commanding officers or the people you command -- as a sign of weakness."
Rizzo said this generation "grew up digital. They're used to this technology, and they can look at it as another type of training."
"It's like a video game to them at first," Spira added. "And then after awhile, it makes it easier for them to talk about the emotional components and integrating back with their family."
Frey agrees. "It's something cool. To a Marine, if something's cool, we're all about it."
Virtual reality therapy is also finding wider use in the civilian world.
Stephen King is a retired New York City fire chief who was at the World Trade Center on Sept. 11, 2001. He was so traumatized by what he saw there that he could no longer come into Manhattan after the attacks, unable to drive over the Brooklyn Bridge.
"After 9/11," King said, "I was afraid that that bridge was going to get blown up when I was halfway over it."
He tried traditional therapy and medication for about a year, but says there came a point where he wasn't getting any better. That's when King turned to virtual reality therapy under the watch of psychologist JoAnn Difede, director of the Program for Anxiety and Traumatic Stress Studies at New York Presbyterian Hospital's Weill Cornell Medical Center.
King was gradually exposed to a computer simulation that shows airplanes crashing into the twin towers, smoke rising and the towers collapsing.
"When I first saw it I said, 'This can't help me. This is like a video game,' " the veteran firefighter said. "But it was anything but that. It's funny. I watched this animated scenario, but for me it was the real buildings, the real people that I saw jumping that day."
After a dozen virtual reality sessions, King is no longer showing the symptoms of PTSD or taking medication, and says he's come a long way from the days when he couldn't cross the Brooklyn Bridge.
"I said, 'Holy smokes, I'm never going want to go into the city again -- go over a bridge, go into a tunnel or whatever,'" he said, pausing. "And I can do those things now."
Difide says that while the preliminary data is excellent, the effectiveness of virtual reality therapy hasn't yet been proven scientifically. But she is pleasantly surprised at how well it works in the patients she has treated.
"As a scientist, I'm still trying to study it and figure it out," she said. "We think it works, but why?"
The military's study of virtual reality will also address the issue of whether the treatment works better than traditional therapies. About 20 military personnel have been treated so far by Spira, who says about 160 patients are expected to receive the therapy over the course of the four-year study. Already, he is encouraged.
"This really speeds up their progress, much faster than traditional talk therapy has been able to do," said Spira, who points out that the more traditional course of talk therapy lasts a couple of years. In contrast, Spira reports the virtual reality treatment has been able to help people beat PTSD in about three months.
For Joshua Frey, that day can't come too soon.
"Before I couldn't move and I didn't want to move. I just wanted to sit there and just dwell and just think and be depressed," he said. "And now I'm actually doing things, going out for walks, getting out and trying to be around people. I want to go back to just being happy and just relaxing, and living in the now and not in the past."