## 2 Related Work
### Asymmetric VR  
Asymmetric VR is a relatively novel branch of VR-related research that explores the use of VR among devices of different immersion and control levels, focusing on the experiences of non-HMD users [13]. The asymmetry occurs when users access the same virtual environment or system using a different technology (for instance, HMD and a desktop-based user interface), which cause uneven experiences and difference in interactions and control. The term \"asymmetry\" took its roots from studies on telepresence and telecollaboration [12]--when symmetric access to virtual environments was reconsidered by virtually recreating a real environment and allowing remote participants to access it. However, in recent years, the research on asymmetric VR was focused on the use of VR for collaboration in co-located settings [13; 14; 15; 19], whereas distributed asymmetric VR gained less attention and was mentioned as a cross-platform multi-user VR [14]. Several studies have investigated the appliance of VR in combination with other technologies of mixed-reality continuum or wearables [15; 21; 22; 23], contributing to a better understanding of immersion, presence, and social interactions of non-HMD users. For example, [PERSON] et. al. [24] presented a low-asymmetry interface, which increases the presence and immersion of non-HMD users by providing a first-person view and realistic movements in a virtual environment based on a portable tracking device. Another study [15] proposed to increase the presence and enjoyment of non-HMD users with floor projection, additional mobile displays, and positional tracking.  
Further, [PERSON] and [PERSON] [14] attempted to characterize how co-located VR asymmetry occurs and how it affects collaboration building on the incorporate theory from the Computer-Supported Cooperative Work (CSCW) field. Their article presented a composite framework of co-located asymmetric VR (CAVR) and introduced the dimensions of asymmetry: three technology-related (transportation, spatial co-presence, informational richness) and two interpersonal experiences--related (team interdependence, and balance of power). Another study [9], which may be applied to distributed asymmetry, defined the degrees of asymmetry as low, medium, and high and suggested defining it based on the interactivity of non-HMD users (also referred as non-VR users). The users of asymmetric VR, therefore, are divided into an actor, who perceives the space through an HMD, and an assistant,who participates in a less immersive manner, while the interactivity of the assistant, which ranges from direct control to absence of control, defines the degrees of asymmetry.  
The topic of collaboration via asymmetric VR gained increased interest during the COVID-19 pandemic's remote work enforcement [25], leading to the exploration of asymmetry in distributed settings [16; 18; 19; 26; 27]. For example, [PERSON] et al. [19] presented a scalable cross-platform prototype that allows communication interactions between a single VR user and multiple non-HMD users on a standard web browser. Further, [PERSON] et al. [18] compared experiences of VR and non-HMD users in a similar setup in the context of immersive analytics and reported overall good user engagement, usability, and collaboration flow despite asymmetry. Another study [16] presented a low-cost approach to the asymmetry between Microsoft Teams and multi-user VR, demonstrating positive effects on collaboration between multidisciplinary teams and enhanced spatial understanding of non-HMD users. Despite the asymmetric VR showing the capability to advance distributed and co-located collaboration, there is a lack of understanding of how it affects learning [28], which results in no clear understanding of how to apply asymmetric set-up for industrial VR-based training to ensure beneficial effects on learning outcomes.