We present HMD Light, a proof-of-concept Head-Mounted Display (HMD) implementation that reveals the Virtual Reality (VR) user's experience in the physical environment to facilitate communication between VR and external users in a mobile VR context. While previous work externalized the VR user's experience through an on-HMD display, HMD Light places the display into the physical environment to enable larger display and interaction area. This work explores the interaction design space of HMD Light and presents four applications to demonstrate its versatility. Our exploratory user study observed participant pairs experience applications with HMD Light and evaluated usability, accessibility and social presence between users. From the results, we distill design insights for HMD Light and asymmetric VR collaboration.

We present Pull-Ups, a suspension kit that can suggest a range of body postures and thus enables various exercise styles of users perceiving the kinesthetic force feedback by suspending their weight with arm exertion during the interaction. Pull-Ups actuates the user's body to move up to 15 cm by pulling his or her hands using a pair of pneumatic artificial muscle groups. Our studies informed the discernible kinesthetic force feedbacks that were then exploited for the design of kinesthetic force feedback in three physical activities: kitesurfing, paragliding, and space invader. Our final study on user experiences suggested that a passive suspension kit alone added substantially to users' perceptions of realism and enjoyment (all above neutral) with passive physical support, while sufficient active feedback can further level them up. In addition, we found that both passive and active feedback of the suspension kit significantly reduced motion sickness in simulated kitesurfing and paragliding compared to when no suspension kit (thus no feedback) was provided. This work suggests that a passive suspension kit is cost-effective as a home exercise kit, while active feedback can further level up user experience, though at the cost of the installation (e.g., an air compressor in our prototype).