## 2 Analysis of VRET Tools Used for the PTSD Treatment
### VR System for Treating Victims of Motor Vehicle Accidents  
One of the first studies using VR to treat PTSD related to motor vehicle accidents was conducted in 2007 [55]. The VEs used in this study consisted of roads that resembled those that patients used to see in real life, with four types of scenes available: highway, urban, suburban, and rural. The patient viewed these scenes through stereoscopic glasses. Depending on the specific exposure situation, the patient could experience each session as a passenger or a driver, with the therapist taking the other role. The device comprised a movement base with six degrees of freedom, equipped with a steering wheel, an accelerator pedal, and a brake pedal. Visual, auditory, and tactile stimuli were used to alter the anxiety levels of the rendered scene. During the sessions, the therapist was able to modify several parameters, including the density and the type of traffic, the time of day, weather conditions, and specific driving events.  
This tool was tested with six patients who had PTSD following motor vehicle accidents [55]. The authors reported an average reduction in PTSD symptoms of around 43% at the end of the treatment. It must nonetheless be noted that while eight patients had been recruited, two dropped out before the fifth session.  
[PERSON] et al. [12], [PERSON] et al. [56] and, later, [PERSON] et al. [15] instituted a VR truck-driving simulator and proposed a new way of approaching VRET. They argued that the traditional methods of exposure therapy treatment emphasize the patient's exposure to frightening stimuli without allowing the patient to act. Consequently, in their simulator, they prioritized the patient's behaviour when faced with anxiety-provoking stimuli. They also highlighted the necessity of creating a VE that not only provides stimuli adapted to the patient's mental state but also allows the patient to be active. These aims were achieved through gamification and personalization of the truck-driving simulator. The gamification process was enforced by linking game mechanics to learning mechanics while basing the VE on the main characteristics of a serious game (SG). The personalization process was intended to create, for each patient, a VE similar to that of the patient's traumatic environment that was capable of prompting emotions and offering flexible scenarios. An environment editor that was easily customizable by the therapist was also incorporated. Aspects that could be adapted to a particular patient's circumstances included the characteristics of the roads and the truck as well as weather conditions. Several devices were used for the exposure, including an HMD to facilitate visual exploration of the scene; for driving, a system consisting of a steering wheel, a gearbox, and pedals was used. This device allowed users to move the truck as they would in reality and offered other basic features such as light, sounds, and wipers.  
This system was used in a case study to treat a truck driver with PTSD following a traffic accident [15]. The patient had previously received another form of therapy without success and was taking medication. The treatment involved placing the patient--and the patient's actions--at the centre of the process. The authors were concerned with developing a tool that enabled the patient to engage with the VE through precise interaction mechanics, such as choosing a truck, driving the truck, and turning on the radio and the windshield wipers. At the end of the treatment, the patient regained control over his life and decided to undertake professional retraining. The authors highlighted the engagement and motivation observed in the patient at each stage of therapy.  
Table 1 summarises the reviewed tools listed from the lowest to highest amount of sensorimotor input.