The Importance of Visual Attention in Improving the 3D-TV Viewing Experience: Overview and New Perspectives <s> B. Vergence and Accommodation <s> Abstract The usual explanation of the disparity-diplopia relationship in terms of retinal fusional areas (Panum's fusional areas) is discussed. Measurements were made of the size of Panum's areas at the fovea, using a method of constant stimuli with flash presentation of the test target to prevent fusional eye movements from influencing the results. Under these conditions little inter- or intra- individual variation was found. In contrast to previous studies, little meridional difference was observed in the amount of disparity necessary to elicit diplopia. Various factors are suggested to explain the relatively large amount of disparity that must be introduced between the two ocular images before diplopia is perceived. <s> BIB001 </s> The Importance of Visual Attention in Improving the 3D-TV Viewing Experience: Overview and New Perspectives <s> B. Vergence and Accommodation <s> Asthenopia, or visual fatigue, is a frequent complaint from observers of stereoscopic three-dimensional displays. It has been proposed that asthenopia is a consequence of anomalous oculomotor responses generated by conflict between accommodative and convergence stimuli. The hypothesis was examined by measuring accommodation and convergence continuously with a Shin-Nippon SRW5000 infrared autorefractor and a limbus tracking device. Subjects viewed a high contrast Maltese Cross target at three levels of Gaussian filter target blur under conditions of relatively low- and high-conflict between accommodation and convergence stimuli, the latter inducing the sensation of stereopsis. Under the low-conflict conditions accommodation was stable, but convergence-driven accommodation was dominant when the target was extremely blurred. Under the high-conflict conditions the role of convergence-driven accommodation increased systematically with the degree of target blur. It is proposed that defocus-driven accommodation becomes weak when the target comprises low spatial frequency components. Large accommodative overshoots to step stimuli that are not blurred or only mildly blurred were consistently observed and are attributed to the initial accommodative response being convergence-driven. Whereas the possibility that high-conflict conditions are a cause of asthenopia has been previously reported, this is the first evidence that they specifically affect accommodative responses while viewing stereoscopic displays. © 2005 Elsevier Ltd. All rights reserved. <s> BIB002 </s> The Importance of Visual Attention in Improving the 3D-TV Viewing Experience: Overview and New Perspectives <s> B. Vergence and Accommodation <s> Three-dimensional (3D) displays have become important for many applications including vision research, operation of remote devices, medical imaging, surgical training, scientific visualization, virtual prototyping, and more. In many of these applications, it is important for the graphic image to create a faithful impression of the 3D structure of the portrayed object or scene. Unfortunately, 3D displays often yield distortions in perceived 3D structure compared with the percepts of the real scenes the displays depict. A likely cause of such distortions is the fact that computer displays present images on one surface. Thus, focus cues-accommodation and blur in the retinal image-specify the depth of the display rather than the depths in the depicted scene. Additionally, the uncoupling of vergence and accommodation required by 3D displays frequently reduces one's ability to fuse the binocular stimulus and causes discomfort and fatigue for the viewer. We have developed a novel 3D display that presents focus cues that are correct or nearly correct for the depicted scene. We used this display to evaluate the influence of focus cues on perceptual distortions, fusion failures, and fatigue. We show that when focus cues are correct or nearly correct, (1) the time required to identify a stereoscopic stimulus is reduced, (2) stereoacuity in a time-limited task is increased, (3) distortions in perceived depth are reduced, and (4) viewer fatigue and discomfort are reduced. We discuss the implications of this work for vision research and the design and use of displays. <s> BIB003
Vergence and accommodation are mechanisms of the HVS that are closely linked and work together when the eyes view visual information in the real world. However, this is not the case with the display of 3D content on a television. On the one hand, as stated before, the eyes focus on the screen because objects appear sharpest on the display plane. On the other hand, the disparity of the objects between the left and the right eyes (or views) leads to a convergence of the eyes towards a point in front or behind the display plane, i.e., depicted objects can appear outside of the screen plane. In the real world, an examined object is located at a certain position in space; therefore, the accommodation and vergence are in synchronization. When the human observer changes its attention to a different location in depth, both accommodation and vergence change at the same time. For the HVS, a change in accommodation induces an automatic change in vergence and vice-versa. The influence of blurred targets to the response of this coupling has been analyzed by Okada et al. BIB002 . When the human observer accommodates and converges on a certain point in depth, his/her vision is able to perceive objects within a certain range using stereopsis while objects farther away are not fused. The area in which fusion is possible is referred to as Panum's area and extends approximately 0.2-0.3 diopters. In order to avoid visual fatigue due to accommodation-vergence conflict, it has been suggested to restrict the displayed depth range to this region BIB003 . Currently, the extent of this area is modeled as a maximum and minimum allowed vergence in front and at the back of the screen. The consequences for displaying content from different sources and thus different disparities on typical 3D screens and the relationship to typical viewing distances has been shown recently in  . However, the size of the Panum's area depends on the extent of the targets, their spatial frequency, and the time of adaptation and a more sophisticated approach may be necessary. It also changes dramatically with the eccentricity as measured relative to the fovea. It has been reported that the fusion limit may be as small as 0.16 degrees in the fovea but reaches 0.5 degrees at 6 degrees eccentricity  , BIB001 . We hypothesize that the consequence might be that a certain combination of objects can be fused in the peripheral vision but when it attracts attention later, it may happen that the observer is not able to fuse it anymore when in foveal vision. The simple assumption that the observer stays focused on the center of the screen may not be correct, in particular when large viewing angles and high-definition content is displayed. Concerning this specific conflict, it is intuitive to think that knowing the position of objects that have the potential to attract visual attention becomes very useful.