The Importance of Visual Attention in Improving the 3D-TV Viewing Experience: Overview and New Perspectives <s> G. Increase of Visual Comfort With Blurring Effects <s> Two possible explanations are presented for the mechanism which limits the maximum fusional vergence response. An experimental paradigm is developed to differentiate between these alternatives. Experimental results indicate that the blur generally associated with strong fusional effort is due to convergence accommodation "overdrive." Th important theoretical and clinical implications of this finding are presented. <s> BIB001 </s> The Importance of Visual Attention in Improving the 3D-TV Viewing Experience: Overview and New Perspectives <s> G. Increase of Visual Comfort With Blurring Effects <s> Abstract Three-dimensional displays provide an unambiguous visual representation of the spatial structure of natural scenes and computer-generated virtual environments and thus have proven substantial advantages over conventional displays in remote guidance and inspection tasks and in application fields such as medical imagery and architectural and molecular modelling. Recent years have seen increasing efforts to extend 3D technologies into the domain of image communications. These efforts received support from human factors studies indicating that 3D displays are highly appreciated by prospective users of image communications systems for their enhanced psychological effects (telepresence and communicative presence). On the other hand, these studies have revealed heavy technological requirements that must be met in order to avoid visible image distortions and increased visual strain. <s> BIB002 </s> The Importance of Visual Attention in Improving the 3D-TV Viewing Experience: Overview and New Perspectives <s> G. Increase of Visual Comfort With Blurring Effects <s> This paper points out that the fusional limits of binocular stereoscopic viewing are an important factor, not only determining the reproduction range of stereoscopic images, but also the conformity between the stereoscopic display and stereoscopic vision. Experimental results showed that fusional limits increase in proportion to the field of view angle, and that they are affected not only by the size of the viewing target, but also by the effects that the environment has on the target. These findings explain the differences between binocular vision in real space and binocular vision in a stereoscopic display. Finally, the conditions under which observers arc able to view images of stereoscopic displays without excessive visual strain are discussed. <s> BIB003 </s> The Importance of Visual Attention in Improving the 3D-TV Viewing Experience: Overview and New Perspectives <s> G. Increase of Visual Comfort With Blurring Effects <s> We present a video-based, contact-free measurement system which allows combined tracking of the subject's eye positions and the gaze direction in near real time. This system will be integrated into a new kind of autostereoscopic display which supports the natural link between accommodation and convergence of human vision, reproduces the limited depth of focus of human vision and shows comfortable, hologram-like scenes with motion parallax to subjects. <s> BIB004 </s> The Importance of Visual Attention in Improving the 3D-TV Viewing Experience: Overview and New Perspectives <s> G. Increase of Visual Comfort With Blurring Effects <s> Depth-of-focus limitations introduce spatial blur in images of three-dimensional scenes. It is not clear how the visual system combines depth information derived from image blur with information from other depth cues. Stereoscopic disparity is the pre-eminent depth cue, so experiments were conducted to investigate interactions between image blur and stereoscopic disparity. Observers viewed two random dot stereograms (RDSs) in a 2AFC task, and were required to identify the RDS depicting the greatest depth. In control observations, all dots in both RDSs were sharply defined. In experimental observations, one RDS contained only sharply defined dots, but the other contained differential spatial blur to introduce an additional depth cue. Results showed that the addition of differential blur made only a marginal difference to apparent depth separation, and only when the blur difference was consistent with the sign of disparity. Cue combination between blur and disparity cues is thus weighted very heavily in favour of the latter. It is shown that blur and disparity cues co-vary according to geometric optics. Since the two cues are effective over different distances, the visual system is not normally called upon to integrate them, and is most likely to make use of blur cues over distances beyond the range of disparity mechanisms. <s> BIB005 </s> The Importance of Visual Attention in Improving the 3D-TV Viewing Experience: Overview and New Perspectives <s> G. Increase of Visual Comfort With Blurring Effects <s> Visual discomfort has been the subject of considerable research in relation to stereoscopic and autostereoscopic displays. In this paper, the importance of various causes and aspects of visual discomfort is clarified. When disparity values do not surpass a limit of 1°, which still provides sufficient range to allow satisfactory depth perception in stereoscopic television, classical determinants such as excessive binocular parallax and accommodation-vergence conflict appear to be of minor importance. Visual discomfort, however, may still occur within this limit and we believe the following factors to be the most pertinent in contributing to this: (1) temporally changing demand of accommodation-vergence linkage, e.g., by fast motion in depth; (2) three-dimensional artifacts resulting from insufficient depth information in the incoming data signal yielding spatial and temporal inconsistencies; and (3) unnatural blur. In order to adequately characterize and understand visual discomfort, multiple types of measurements, both objective and subjective, are required. <s> BIB006 </s> The Importance of Visual Attention in Improving the 3D-TV Viewing Experience: Overview and New Perspectives <s> G. Increase of Visual Comfort With Blurring Effects <s> In this paper we analyze and try to predict the gaze behavior of users navigating in virtual environments. We focus on first-person navigation in virtual environments which involves forward and backward motions on a ground-surface with turns toward the left or right. We found that gaze behavior in virtual reality, with input devices like mice and keyboards, is similar to the one observed in real life. Participants anticipated turns as in real life conditions, i.e. when they can actually move their body and head. We also found influences of visual occlusions and optic flow similar to the ones reported in existing literature on real navigations. Then, we propose three simple gaze prediction models taking as input: (1) the motion of the user as given by the rotation velocity of the camera on the yaw axis (considered here as the virtual heading direction), and/or (2) the optic flow on screen. These models were tested with data collected in various virtual environments. Results show that these models can significantly improve the prediction of gaze position on screen, especially when turning, in the virtual environment. The model based on rotation velocity of the camera seems to be the best trade-off between simplicity and efficiency. We suggest that these models could be used in several interactive applications using gaze point as input. They could also be used as a new top-down component in any existing visual attention model. <s> BIB007
Comfortable viewing conditions, i.e., zone of comfortable viewing, of stereoscopic content is linked to several factors among which range of depth of focus and range of fusion BIB002 , BIB003 . For instance, Wöpking's studies  suggest that visual discomfort increases with high spatial frequencies and disparities. This is partially explained by the fact that the limits of fusion increase as a result of the decreased spatial frequency. More generally, it appears that blurring effects can positively impact visual comfort because they reduce the accommodation-vergence conflict limiting both accommodation and effort to fuse BIB001 , BIB004 . As the distance from the fixation point increases, objects are perceived more and more blurred. Blur in this sense may be used to mimic the perception of retinal defocus, which will lead to the sought positive effect in visual comfort. Simulating depth-of-field (DOF) is a way to take advantage of this property, by artificially blurring images to a degree that corresponds to the relative depth or distance from fixated objects. As reported by Lambooij et al. BIB006 , "three essential steps are required for proper implementation of a simulated DOF: localization of the eye positions, determination of the fixation point and implementation of blur filters to non-fixated layers". This procedure has been applied in virtual reality environment but is still subject to some drawbacks in more general contexts (depth cues integration between retinal disparity and high amount of blur BIB005 ). Blurring effects can also be used in 3D content to direct the viewer's attention towards a specific area of the image that should fit ideally in a zone of comfortable viewing. Although gaming is not a topic of interest in this paper, we can however mention that visual attention modeling has attracted a growing interest from the computer graphics community, especially for virtual environments. The use of visual attention models has been proposed to produce a more realistic behavior of a virtual character, to improve interactivity in 3D virtual environments and to improve the visual comfort of the rendering of 3D virtual environments  ,  , BIB007 .