Virtual Reality
Virtual Reality provides a new way of experiencing virtual content with unprecedented capabilities that have the potential of profoundly impact our society. However little is known about how this new scenario influences users’ perception. Our research efforts are targeted towards understanding viewers’ behavior in immersive VR environments.
With the proliferation of low-cost, consumer level head-mounted displays (HMDs), Virtual Reality (VR) is progressively entering the consumer market. VR systems provide a new way of experiencing virtual content that is richer than radio, or television, yet also different from how we experience the real world. These unprecedented capabilities for creating new content have the potential to profoundly impact our society. However, little is known about how this new scenario may affect users’ behavior, especially in narrative VR: How does one design or edit 3D scenes effectively in order to retain or guide users’ attention? Can we predict users’ behavior and react accordingly? How does one create a satisfactory cinematic VR cinematic experience? On a more fundamental level, our understanding of how to tell stories may have to be revised for VR. To derive conventions for storytelling from first principles, it is crucial to understand how users explore virtual environments and what constitutes attention. Such an understanding would also inform future designs of user interfaces, eye tracking technology, and other key aspects of VR systems.
Funding agencies
Publications
Imperceptible manipulation of lateral camera motion for improved virtual reality applications
Ana Serrano*, Daniel Martín*, Diego Gutierrez, Karol Myszkowski, Belen Masia
ACM Transactions on Graphics, Vol. 39(6) (SIGGRAPH Asia 2020)
Abstract: Virtual Reality (VR) systems increase immersion by reproducing users’ move- ments in the real world. However, several works have shown that this real- to-virtual mapping does not need to be precise in order to convey a realistic experience. Being able to alter this mapping has many potential applications, since achieving an accurate real-to-virtual mapping is not always possible due to limitations in the capture or display hardware, or in the physical space available. In this work, we measure detection thresholds for lateral translation gains of virtual camera motion in response to the corresponding head motion under natural viewing, and in the absence of locomotion, so that virtual camera movement can be either compressed or expanded while these manipulations remain undetected. Finally, we propose three applications for our method, addressing three key problems in VR: improving 6-DoF viewing for captured 360◦ footage, overcoming physical constraints, and reducing simulator sickness. We have further validated our thresholds and evaluated our applications by means of additional user studies confirming that our ma- nipulations remain imperceptible, and showing that (i) compressing virtual camera motion reduces visible artifacts in 6-DoF, hence improving perceived quality, (ii) virtual expansion allows for completion of virtual tasks within a reduced physical space, and (iii) simulator sickness may be alleviated in simple scenarios when our compression method is applied.
Auditory stimuli degrade visual performance in virtual reality
Sandra Malpica, Ana Serrano, Diego Gutierrez, Belen Masia
Scientific Reports (Nature Publishing Group)
Abstract: We report an auditory effect of visual performance degradation in a virtual reality (VR) setting, where the viewing conditions are significantly different from previous studies. With the presentation of temporally congruent but spatially incongruent sound, we can degrade visual performance significantly at detection and recognition levels. We further show that this effect is robust to different types and locations of both auditory and visual stimuli. We also analyze participants behavior with an eye tracker to study the underlying cause of the degradation effect. We find that the performance degradation occurs even in the absence of saccades towards the sound source, during normal gaze behavior. This suggests that this effect is not caused by oculomotor phenomena, but rather by neural interactions or attentional shifts.
Exploring the impact of 360º movie cuts in users' attention
Carlos Marañes, Diego Gutierrez, and Ana Serrano
IEEE VR 2020
Abstract: Virtual Reality (VR) has grown since the first devices for personal use became available on the market. However, the production of cinematographic content in this new medium is still in an early exploratory phase. The main reason is that cinematographic language in VR is still under development, and we still need to learn how to tell stories effectively. A key element in traditional film editing is the use of different cutting techniques, in order to transition seamlessly from one sequence to another. A fundamental aspect of these techniques is the placement and control over the camera. However, VR content creators do not have full control of the camera. Instead, users in VR can freely explore the 360◦ of the scene around them, which potentially leads to very different experiences. While this is desirable in certain applications such as VR games, it may hinder the experience in narrative VR. In this work, we perform a systematic analysis of users’ viewing behavior across cut boundaries while watching professionally edited, narrative 360◦ videos. We extend previous metrics for quantifying user behavior in order to support more complex and realistic footage, and we introduce two new metrics that allow us to measure users’ exploration in a variety of different complex scenarios. From this analysis, (i) we confirm that previous insights derived for simple content hold for professionally edited content, and (ii) we derive new insights that could potentially influence VR content creation, informing creators about the impact of different cuts in the audience’s behavior.
Panoramic convolutions for 360º single-image saliency prediction
Daniel Martin, Ana Serrano, Belen Masia
CVPR Workshop on Computer Vision for Augmented and Virtual Reality 2020
Abstract: We present a convolutional neural network based on panoramic convolutions for saliency prediction in 360º equirectangular panoramas. Our network architecture is designed leveraging recently presented 360º-aware convolutions that represent kernels as patches tangent to the sphere where the panorama is projected, and a spherical loss function that penalizes prediction errors for each pixel depending on its coordinates in a gnomonic projection. Our model is able to successfully predict saliency in 360º scenes from a single image, outperforming other state of-the-art approaches for panoramic content, and yielding more precise results that may help in the understanding of users’ behavior when viewing 360º VR content.
Motion parallax for 360 RGBD video
Ana Serrano, Incheol Kim, Zhili Chen, Stephen DiVerdi, Diego Gutierrez, Aaron Hertzmann, Belen Masia
IEEE Transactions on Visualization and Computer Graphics, Vol. 25(5) (IEEE VR 2019)
Abstract: We present a method for adding parallax and real-time playback of 360° videos in Virtual Reality headsets. In current video players, the playback does not respond to translational head movement, which reduces the feeling of immersion, and causes motion sickness for some viewers. Given a 360° video and its corresponding depth (provided by current stereo 360 stitching algorithms), a naive image-based rendering approach would use the depth to generate a 3D mesh around the viewer, then translate it appropriately as the viewer moves their head. However, this approach breaks at depth discontinuities, showing visible distortions, while cutting the mesh at such discontinuities leads to ragged silhouettes and holes at disocclusions. We address these issues by improving the given initial depth map to yield cleaner, more natural silhouettes. We rely on a three-layer scene representation, made up of a foreground layer and two static background layers, to handle disocclusions by propagating information from multiple frames for the first background layer, and then inpainting for the second one. Our system works with input from many of today's most popular 360 stereo capture devices (e.g., Yi Halo or GoPro Odyssey), and works well even if the original video does not provide depth information. Our user studies confirm that our method provides a more compelling viewing experience, increasing immersion while reducing discomfort and nausea.
Crossmodal Perception in Virtual Reality
Sandra Malpica, Ana Serrano, Marcos Allue, Manuel Bedia, Belen Masia
Multimedia Tools and Applications, 2019
Abstract: With the proliferation of low-cost, consumer level, head-mounted displays (HMDs) we are witnessing a reappearance of virtual reality. However, there are still important stumbling blocks that hinder the achievable visual quality of the results. Knowledge of human perception in virtual environments can help overcome these limitations. In this work, within the much-studied area of perception in virtual environments, we look into the less explored area of crossmodal perception, that is, the interaction of different senses when perceiving the environment. In particular, we look at the influence of sound on visual perception in a virtual reality scenario. First, we assert the existence of a crossmodal visuo-auditory effect in a VR scenario through two experiments, and find that, similar to what has been reported in conventional displays, our visual perception is affected by auditory stimuli in a VR setup. The crossmodal effect in VR is, however, lower than that present in a conventional display counterpart. Having asserted the effect, a third experiment looks at visuo-auditory crossmodality in the context of material appearance perception. We test different rendering qualities, together with the presence of sound, for a series of materials. The goal of the third experiment is twofold: testing whether known interactions in traditional displays hold in VR, and finding insights that can have practical applications in VR content generation (e.g., by reducing rendering costs)
How do people explore virtual environments?
Vincent Sitzmann*, Ana Serrano*, Amy Pavel, Maneesh Agrawala, Diego Gutierrez, Belen Masia, and Gordon Wetzstein
IEEE Transactions on Visualization and Computer Graphics, Vol. 24 (IEEE VR 2018)
Abstract: Understanding how humans explore virtual environments is crucial for many applications, such as developing compression algorithms or designing effective cinematic virtual reality (VR) content, as well as to develop predictive computational models. We have recorded 780 head and gaze trajectories from 86 users exploring omnidirectional stereo panoramas using VR head-mounted displays. By analyzing the interplay between visual stimuli, head orientation, and gaze direction, we demonstrate patterns and biases of how people explore these panoramas and we present first steps toward predicting time-dependent saliency. To compare how visual attention and saliency in VR are different from conventional viewing conditions, we have also recorded users observing the same scenes in a desktop setup. Based on this data, we show how to adapt existing saliency predictors to VR, so that insights and tools developed for predicting saliency in desktop scenarios may directly transfer to these immersive applications.
Movie Editing and Cognitive Event Segmentation in Virtual Reality Video
Ana Serrano, Vincent Sitzmann, Jaime Ruiz-Borau, Gordon Wetzstein, Diego Gutierrez, and Belen Masia
ACM Transactions on Graphics, Vol. 36(4) (SIGGRAPH 2017)
Abstract: Traditional cinematography has relied for over a century on a well-established set of editing rules, called continuity editing, to create a sense of situational continuity. Despite massive changes in visual content across cuts, viewers in general experience no trouble perceiving the discontinuous flow of information as a coherent set of events. However, Virtual Reality (VR) movies are intrinsically different from traditional movies in that the viewer controls the camera orientation at all times. As a consequence, common editing techniques that rely on camera orientations, zooms, etc., cannot be used. In this paper we investigate key relevant questions to understand how well traditional movie editing carries over to VR, such as: Does the perception of continuity hold across edit boundaries? Under which conditions? Does viewers’ observational behavior change after the cuts? To do so, we rely on recent cognition studies and the event segmentation theory, which states that our brains segment continuous actions into a series of discrete, meaningful events. We first replicate one of these studies to assess whether the predictions of such theory can be applied to VR. We next gather gaze data from viewers watching VR videos containing different edits with varying parameters, and provide the first systematic analysis of viewers’ behavior and the perception of continuity in VR. From this analysis we make a series of relevant findings; for instance, our data suggests that predictions from the cognitive event segmentation theory are useful guides for VR editing; that different types of edits are equally well understood in terms of continuity; and that spatial misalignments between regions of interest at the edit boundaries favor a more exploratory behavior even after viewers have fixated on a new region of interest. In addition, we propose a number of metrics to describe viewers’ attentional behavior in VR. We believe the insights derived from our work can be useful as guidelines for VR content creation.
Crossmodal perception in immersive environments
Marcos Allue, Ana Serrano, Manuel G. Bedia and Belen Masia
Spanish Computer Graphics Conference (CEIG), 2016
Abstract: With the proliferation of low-cost, consumer level, head-mounted displays (HMDs) such as Oculus VR or Sony’s Morpheus, we are witnessing a reappearance of virtual reality. However, there are still important stumbling blocks that hinder the development of applications and reduce the visual quality of the results. Knowledge of human perception in virtual environments can help overcome these limitations. In this paper, within the much-studied area of perception in virtual environments, we chose to look into the less explored area of crossmodal perception, that is, the interaction of different senses when perceiving the environment. In particular, we looked at the influence of sound on visual motion perception in a virtual reality scenario. We first replicated a well-known crossmodal perception experiment, carried out on a conventional 2D display, and then extended it to a 3D headmounted display (HMD). Next, we performed an additional experiment in which we increased the complexity of the stimuli of the previous experiment, to test whether the effects observed would hold in more realistic scenes. We found that the trend which was previously observed in 2D displays is maintained in HMDs, but with an observed reduction of the crossmodal effect. With more complex stimuli the trend holds, and the crossmodal effect is further reduced, possibly due to the presence of additional visual cues.