Exploring the design space of eyes-free target acquisition in virtual environments

Supporting smooth target acquisition is an important objective in immersive virtual reality (VR) environments. However, users were obliged to search for objects relying on the vision channel in traditional VR systems. Such eyes-engaged technologies may significantly degrade the interaction efficiency and user experience, particularly when users have to turn their head frequently to search for virtual objects in the limited field of view of a head-mounted display. In this paper, we report a two-stage study which investigates the capability of VR users to acquire spatial targets without eye engagement (i.e., eyes-free target acquisition). First, we measure the eyes-free performance of users in terms of control accuracy and subjective task load. Second, we evaluate the effects of eyes-free acquisition on memory capacity, spatial offset, and task completion time in the context of a VR game. Starting from a set of 54 spatial positions, we identify 18 optimal locations (half on the left side of the user’s body and half on the right) that allow both accurate and comfortable target acquisition without visual attention. After a short training period, users could accurately and quickly acquire 17 targets in a VR game with an average offset of 10.5 cm and an average completion time of 2.7 s. According to our results, we suggest how to optimize the spatial layout, number of targets, target locations, and interaction techniques for eyes-free acquisition in VR applications. Our work can serve as a foundation for future development of eyes-free methods of target acquisition in VR.