CHANGE BLINDNESS PHENOMENA FOR VIRTUAL REALITY DISPLAY SYSTEMS 1 Change Blindness Phenomena for Virtual Reality Display Systems Frank Steinicke, Member, IEEE , Gerd Bruder, Student Member, IEEE , Klaus Hinrichs Member, IEEE , Pete Willemsen, Member, IEEE Abstract—In visual perception, change blindness describes the phenomenon that persons viewing a visual scene may apparently fail to detect significant changes in that scene. These phenomena have been observed in both computer generated imagery and real-world scenes. Several studies have demonstrated that change blindness effects occur primarily during visual disruptions such as blinks or saccadic eye movements. However, until now the influence of stereoscopic vision on change blindness has not been studied thoroughly in the context of visual perception research. In this article we introduce change blindness techniques for stereoscopic virtual reality (VR) systems, providing the ability to substantially modify a virtual scene in a manner that is difficult for observers to perceive. We evaluate techniques for semi-immersive VR systems, i. e., a passive and active stereoscopic projection system as well as an immersive VR system, i. e., a head-mounted display, and compare the results to those of monoscopic viewing conditions. For stereoscopic viewing conditions, we found that change blindness phenomena occur with the same magnitude as in monoscopic viewing conditions. Furthermore, we have evaluated the potential of the presented techniques for allowing abrupt, and yet significant, changes of a stereoscopically displayed virtual reality environment. Index Terms—Change Blindness, stereoscopic display, virtual reality ✦ 1 I NTRODUCTION V ISUAL attention describes how humans prioritize information in their visual field of view to process complex visual scenes in order to detect, identify, localize and track objects [17], [28]. This allows our visual system to handle subsets of the visual input sequentially by focusing attention to salient locations [9], [28]. 1.1 Inattentional and Change Blindness In this context, inattentional blindness describes the phe- nomenon that human observers fail to notice objects that are in their view due to the circumstance that they focus on other parts of the visual scene [12]. In such situations, modifications to certain objects can literally go unnoticed when the visual attention is not focused on them. Change blindness denotes the inability of the human eye to detect modifications of the scene that are rather obvious–once they have been identified [1], [5], [20]. These scene changes can be of various types and magnitudes, for example, prominent objects could appear and disappear, change color, or shift position by a few degrees [23]. Such change blindness effects occur for both static pictures as well as dynamic scenes [19], [22]. Figure 1 shows an example of such a change. In Figure 1(c) and (d) the spire within the frame has shifted position in comparison to Figure 1(a) and (b), respectively. The red frames highlight • Frank Steinicke, Gerd Bruder and Klaus Hinrichs are with the Insti- tute of Computer Science, University of M ¨ unster, Germany, E-mail: {fsteini|g brud01|khh}@uni-muenster.de. • Pete Willemsen is with the Department of Computer Science, University of Minnesota Duluth, USA, E-mail: willemsn@d.umn.edu. the difference between the two images and are used for illustration purposes only. 1.2 Virtual Reality Display Systems Such change blindness effects have great potential for computer-generated environments, in particular virtual reality (VR) systems, since they allow abrupt changes of the visual scene which are unnoticeable for users. VR systems usually employ semi- or fully-immersive displays to immerse users into the virtual world [3]. Active or passive stereoscopic projection systems like powerwalls or workbenches are considered as semi- immersive, whereas head-mounted displays (HMDs) or CAVE environments are considered as (fully-)immersive VR display systems. In a semi-immersive VR display environment usually the user can perceive the physical surroundings of the laboratory, whereas in an immersive VR display environment these physical surroundings are blocked out such that the user perceives only the virtual world. Which technology is more appropriate for a given situation depends on the application. For instance, if it is important to immerse the user in the virtual world and provide a high level of feeling present in the VE, a fully-immersive VR display system is beneficial, whereas if multiple users should explore a VE in collaboration, semi-immersive VR environments may be more appro- priate. 1.3 Perception in Virtual Environments Current research on human perception in virtual environments (VEs) focuses on identifying just- noticeable differences and detection thresholds that