On an Orlando college campus, veterans and active duty soldiers suffering from post-traumatic stress disorder inhale the unmistakable smell of burning tires, rotting garbage and Middle Eastern spices as part of a virtual reality treatment for the psychological wounds of war.

Participants sit in a chair wearing a head-mounted display and video goggles connected to a computer system and a scent machine that puffs out the odors, recreating their memories of war, from insurgent ambushes and roadside bombs to witnessing comrades die.

From the outside, it looks like the soldiers are playing a video game, but therapists hope that on the inside, they are healing.

The Trauma Management Therapy program, now available to South Florida active duty soldiers and veterans with PTSD who volunteer, is part of a clinical study at the University of Central Florida that uses sights, sounds and smell to help ease the episodes of anxiety, sleeplessness and nightmares. With new waves of soldiers returning as American forces withdraw from Iraq and Afghanistan, researchers are hoping the combination of traditional therapy and virtual-reality simulation — with an emphasis on smell — to help decrease post-traumatic symptoms.

“The point is not to make people comfortable with these events, but to decrease the emotion that has gone along with them so someone stops being afraid to drive under an overpass because it triggers a reaction related to a bridge attack they lived through in Iraq,” said Deborah Beidel, director of the UCF Anxiety Disorders Clinic. “Think of it this way: If you were afraid of dogs, how do you get past that fear? You have to be around a dog. You have to confront the fear.”

Between 11 percent and 20 percent of veterans of the Iraq and Afghanistan wars have PTSD and more than 200,000 veterans have been treated for the disorder at facilities run by the U.S. Department of Veterans Affairs, statistics that are driving the military to explore alternate treatments including acupuncture, yoga and meditation. The Military Operational Medicine Research Program has invested about $297 million in active research projects addressing PTSD, from prevention to treatment.

Virtual-reality exposure therapy is among the promising tools.

As part of the $5 million study, Beidel is leading a team of therapists who use the Virtual Iraq and Virtual Afghanistan software to simulate war experiences based on the memories of the soldiers. The participants, all from Florida so far, describe in detail the traumas to a therapist who uses the information to create a virtual combat landscape. Participants come in daily for three weeks for 90 minute sessions followed by group therapy. Previous therapies that used the virtual reality software — some minus the scent machine — took longer, usually months. This latest process is faster but still highly controlled, with the soldiers describing their experiences to a therapist who, with the click of a mouse, sets the scene on the computer.

In short, the soldier or veteran is the narrator. The therapist is the producer.

The treatment starts with the participant dropped into a virtual Humvee as a driver or passenger or gun turret operator. The computer program can be tweaked for day or night, sunny or sandstorm, quiet or with helicopters roaring overhead, peaceful or with snipers on rooftops. The truck can rumble along a bustling street with markets or along a desert highway — a platform under the chair is designed to make the chairs vibrate. Chatter can be heard in English or Arabic. Insurgents can be seen lying dead or lurking around corners.