Preventing Imminent Collisions between Co-Located Users in HMD-Based VR in Non-Shared Scenarios

This paper presents two experiments set in amulti-user HMD-based VR system where usersnavigate by real walking in a large real and vir-tual area. We investigate a case that could beused in a multi-user VR game or a training ap-plication: several users are walking in the samephysical space without seeing each other in thevirtual environment. Such a scenario involvesthe risk of collisions between users. In the firstexperiment, we investigate the strategy of stop-ping a walking user in a dangerous situation. Inparticular, we compare the effectiveness and theperceived difficulty of two visual and two audi-tory stopping signals. The results of this com-parison show that the tested visual and auditorysignals are equally effective in stopping users.With both visual and auditory signals, partici-pants prefer the signal to contain a "stop" com-mand. In the second experiment, avatars aredisplayed at users´ positions if the distance be-tween users is dangerously small. The methodis tested with four avatars of various degrees ofanthropomorphism and in two different appli-cation scenarios. Our results suggest that thetype of scenario influences users´ preference ofa notification avatar. It is sufficient to displayan area occupied by other users in scenarioswith specific goals and interactive content. Ifusers are exploring a virtual world without hav-ing any other goal, they prefer to see human-like avatars as a possible collision notification.