## 5 Review of Considered Study
### Natural Environment-Specific Phobia--Height Phobia (Acrophobia)  
Patient interactivity during the virtual reality exposure therapy was enhanced using a Kinect. Kinect has a built-in motion and movement capturing feature presented by Microsoft. Acrophobia Simulator is a game-based virtual reality exposure therapy that runs on an Android smartphone inside a Google Cardboard and a Kinect. The stages include a river, a city and a mountain, respectively. The patient will lose once they fall at any stage. The difficulty is increased at each stage; the river is the easiest stage, while the mountain is the most difficult one. The evaluation was done using an anxiety questionnaire on ten patients with ages ranging between 21 and 25 years [32]. Another study conducted to treat acrophobia and test the treatment effectiveness of virtual reality consists of two realistic levels. Level 1 displays a 3D mountain view, while level 2 contains a 3D city view. The application was integrated into a VR Gear HMD with a Samsung Galaxy S7 smartphone. The patient's movement was detected using a Kinect sensor. A system evaluation was done on a sample size of twenty patients with ages ranging between 20 and 21 years old. Moreover, the selected sample was divided into two groups having the same or a similar anxiety level; one was exposed to the normal exposure therapy, while the other was exposed to the virtual reality exposure therapy. Over two months, eight sessions were conducted. One session per week was each 25 min long. A Body Sensation Interpretation Questionnaire (BSIQ) was used to clarify the anxiety symptoms during the test [34]. Another study was conducted to determine the visibility of remote virtual exposure therapy in comparison to traditional virtual reality exposure therapy. Nevertheless, the study was tested on the same sample but divided into groups to compare. The first group received three virtual exposure therapy sessions remotely, while the second received three virtual reality exposure therapy sessions in the presence of a therapist. An evaluation was conducted on a total of six height phobia patients with ages ranging between 18 and 65 years. The testing duration was three weeks, with a total of six sessions, two in a week. Sony HMZ-T1 HMD is used to display the therapy, with a microphone to allow communication between the patient and the therapist and a webcam to monitor the patient's activity. The patient was exposed to two different virtual worlds, a subway station and a 24-storey tower block. Pre-exposure, the patient must fill in the State-Trait Anxiety Inventory (STAI form Y-A) and rate their anxiety level on a visual analogue scale (VAS). Post-exposure, the patient must fill in anxiety-related questionnaires using a VAS [37]. 0 Phobia is a self-guided mobile game developed to deliver virtual reality exposure therapy easily to every height phobia patient using a VR cardboard. An evaluation was achieved on 180 height patients in total that were randomly assigned to either 0 Phobia or waitlist. The number of measurements used included an acrophobia questionnaire, the Attitudes Towards Heights Questionnaire (ATHQ), Beck Anxiety Inventory (BAI), System Usability Scale (SUS), Igorup Presence Questionnaire (IPQ), Pearlin Mastery Scale, and a Patient Health Questionnaire. However, the app contains six modules each which can be completed in 5 to 20 min. In addition to a virtual therapist that guides the user, the user needs to complete a set of assignments in all the modules. Each assignment aims to expose the user to a different level of height. It also includes four 360 deg videos, including the user standing on top of a high building, crossing a bridge, dangling their legs on a rooftop, or standing on a high crane. In the end, the user gets performance feedback to proceed to the next stage [21]. With the enhancement of virtual reality devices, the user can experience stronger emotions that provide the most realistic experience.