## 2 Materials and Methods
### Task Procedure  
All participants experienced the VR-based interactive feedback program of about 45 min, 'Enhancing Functional Communication' once, that consisted of three tasks, such as exploring the communication style, practicing functional communication, and expressing empathy (Figure 1). The task procedures were identical in all respects to those detailed in the feasibility study of this program [35]. The VR system consisted of a desktop computer, an Oculus Rift head-mounted display with a tracker (Oculus VR LLC, Menlo Park, CA, USA), and the touch controller (Oculus VR LLC, Menlo Park, CA, USA). In all the tasks that were produced using a 3D video shot of the acting of professional actors, participants were advised to consider and talk in detail as they deemed appropriate in the given interpersonal situation. Participants performed all the tasks themselves while sitting on a comfortable sofa, and the researcher provided assistance only for the start and end of the tasks. In the task of exploring the communication style, participants experienced dysfunctional communication in two categories of interpersonal conflict situations: conflict with family and conflict with a friend (Figure 1A-1). Participants experienced two situations in each category in the order given: conflict with family: father and mother, conflict with a friend: male and female friends. Participants should select twice one of five response options reflecting the style of communication (placating, blaming, computing, distracting, and functional) in each situation. Specifically, after hearing emotional remarks from a virtual person, participants made the first choice (Choice 1) from five response options that most closely resembled the response they were most likely to actually make. Then, they experienced the recorded conversation consisting of their own reaction and the reaction from the virtual person corresponding to their selection. After experiencing the recorded conversation, participants had to choose the second selection (Choice 2). The next situation with another virtual person (mother or female friend) in the same category was presented and proceeded in the same way. Participants had to repeat the two situations each time they selected a dysfunctional communication style in any situation, and the task was completed by selecting the option of functional communication in both situations in each category. The number of selections for each dysfunctional communication style made before both categories were repeated was recorded and referred to as NS-placating, NS-blaming, NS-computing, and NS-distracting, respectively (Figure 1A-2). Figure 1: Screenshots and schematic diagrams of enhancing functional communication. Although the tasks were conducted in Korean, the procedure here is explained in English for the convenience of understanding. To protect the portrait rights of the cast, the faces are obscured. Abbreviation: VAS, visual analog scale; NS, the number of selections; CS, communication score. In the task of practicing functional communication, participants interacted with someone who communicated dysfunctionally in four different conflict-driven situations (Figure 1B-1). In each situation, participants listened to and freely responded to one of four dysfunctional communication styles (placating, blaming, computing, or distracting) exhibited by one of two or three others, and then listened to a possible example of functional communication via voice guidance. Next, they rated how close their response was to the presented example using a visual analog scale (VAS), which presented 'not at all' (0) at the left end and'very much' (100) at the right end. The VAS score was referred to as the communication score with the placating, blaming, computing, or distracting style (abbreviation: CS-placating, CS-blaming, CS-computing, and CS-distracting, respectively) (Figure 1B-2).