Augmentation Techniques for Efficient Exploration in Head-Mounted Display Environments Benjamin Bolte * , Gerd Bruder † , Frank Steinicke ‡ , Klaus Hinrichs § Visualization and Computer Graphics Group Department of Computer Science, University of M¨ unster, Germany Markus Lappe ¶ Psychology Department II University of M¨ unster, Germany Abstract Physical characteristics and constraints of today’s head-mounted displays (HMDs) often impair interaction in immersive virtual en- vironments (VEs). For instance, due to the limited field of view (FOV) subtended by the display units in front of the user’s eyes more effort is required to explore a VE by head rotations than for exploration in the real world. In this paper we propose a combination of two augmentation tech- niques that have the potential to make exploration of VEs more ef- ficient: (1) augmenting the geometric FOV (GFOV) used for ren- dering the VE, and (2) amplifying head rotations while the user changes her head orientation. In order to identify how much ma- nipulation can be applied without users noticing, we conducted two psychophysical experiments in which we analyzed subjects’ ability to discriminate between virtual and real head pitch and roll rota- tions while three different geometric FOVs were used. Our results show that the combination of both techniques has great potential to support efficient exploration of VEs. We found that virtual pitch and roll rotations can be amplified by 30% and 44% respectively, when the GFOV matches the subject’s estimation of the most nat- ural FOV. This leads to a possible reduction of the user’s effort re- quired to explore the VE using a combination of both techniques by approximately 25%. CR Categories: I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism—Virtual reality Keywords: Head-mounted displays, head motion perception, ge- ometric field of view 1 Introduction In the real world, long-term evolutionary natural selection opti- mized the complex interplay of human actions and multi-sensory feedback evaluation. In particular, the ability to explore our sur- roundings by means of our eyes and coordinated head motions is very sophisticated. Unfortunately, until now this important abil- ity has not been transferred appropriately to immersive virtual real- ∗ e-mail: b.bolte@uni-muenster.de † e-mail: g brud01@uni-muenster.de ‡ e-mail: fsteini@uni-muenster.de § e-mail: khh@uni-muenster.de ¶ e-mail: mlappe@uni-muenster.de ity (VR) environments. Immersive head-mounted displays (HMDs) are one of the most popular virtual display devices which have the potential to support a natural viewing experience in a virtual world. However, physical characteristics of today’s HMDs such as size, weight, wires, and field of view (FOV) hamper efficient exploration of virtual environments (VEs). For instance, the limited FOV al- lows users to see only a portion of the VE, while most parts that would be visible to humans in the real world due to peripheral vi- sion are blocked. When standing upright in the real world, it is easy for a human to look at her feet by simply pitching her head and eyes downwards by an angle of approximately 45 ◦ . Attempting the same task while wearing a HMD requires the user to bend forward, resulting in more effort as illustrated in Figure 1. Moreover, in HMD environments users have to apply greater mus- cle force to the neck in order to adjust their head posture to com- pensate for the HMD characteristics. Consequently, head move- ments with HMDs often appear cumbersome and constrained, and often it is more strenuous for users to perform specific tasks or even worse, musculoskeletal problems may arise from prolonged posture adoption [Baber et al. 1999]. These arguments underscore the im- portance and need for methods to improve comfort of HMDs and to reduce neck fatigue or even to prevent injury. Although some wide field of view HMDs are available, unfortunately, the trade- off between the HMD’s FOV and the resolution, cost, and weight, makes HMDs with a FOV comparable to human vision unlikely in the foreseeable future [Melzer et al. 2009]. Hence, solutions are highly desirable that do not rely on hardware changes, but reduce the user’s effort required to explore the VE. In order to satisfy this requirement, we propose the combination of two augmentation techniques: • augmenting the geometric FOV (GFOV) used for rendering the VE, and • amplifying head rotations while the user changes her head ori- entation. Considering the first aspect, researchers have proposed to compress visual information in the limited FOV of a HMD by increasing the GFOV that is applied in the rendering process [Kuhl et al. 2009]. But for an undistorted view to the virtual world in a HMD environ- ment the perspective projection in the rendering process has to be adjusted to the FOV of the HMD. Increasing the GFOV augments the virtual aperture angle that is used for rendering the VE and thus reduces the need for head motions in visual search tasks. However, this manipulation distorts the perception of geometry of virtual ob- jects [Steinicke et al. 2009] and spatial relations in the VE [Kuhl et al. 2009], since the virtual scene appears minified. Until now, hardly any research has focused on analyzing the effects of manip- ulating the GFOV, and in particular the impact of such perspective distortions on motion perception has not yet been evaluated. Tracked head rotations, in particular yaw and pitch rotations, en- able natural exploration of VEs. However, due to the limited FOV of HMDs, more frequent and larger head motions are required, for example, in visual search tasks [Alfano and Michel 1996; Jay and Hubbold 2003]. Roll rotations are used primarily in specific tasks,