The Importance of Visual Attention in Improving the 3D-TV Viewing Experience: Overview and New Perspectives <s> A. Depth Cues: Combination and Conflicts <s> Publisher Summary ::: This chapter discusses three questions: Why are there so many sources of information about layout? How is it that one perceives layout with near-metric accuracy when none of these sources yields metric information about it? Can one not do better, theoretically, in understanding the perception of layout than simply make a list? The answer to the first question begins with Todd's answer. Perceiving layout is extremely important to human beings, so important that it must be redundantly specified so that the redundancy can guard against the failure of any given source or the failure of any of the assumptions on which a given source is based. However, information redundancy is only part of the answer. Different sources of information about layout metrically reinforce and contrast with each other, providing a powerful network of constraints. The answer to the second proceeds from this idea. Through the analysis of depth-threshold functions for nine different sources of information about layout, one can begin to understand how those sources of information sharing the same-shaped functions across distances can help ramify judgments of layout by serving to correct measurement errors in each. Third, on the basis of the analyses and the pattern of functions, it suggests that list making has misled about space and layout. Psychologists and other vision scientists have generally considered layout, space, and distance as a uniform commodity in which observers carry out their day-to-day activities. <s> BIB001 </s> The Importance of Visual Attention in Improving the 3D-TV Viewing Experience: Overview and New Perspectives <s> A. Depth Cues: Combination and Conflicts <s> The authors used a virtual environment to investigate visual control of reaching and monocular and binocular perception of egocentric distance, size, and shape. With binocular vision, the results suggested use of disparity matching. This was tested and confirmed in the virtual environment by eliminating other information about contact of hand and target. Elimination of occlusion of hand by target destabilized monocular but not binocular performance. Because the virtual environment entails accommodation of an image beyond reach, the authors predicted overestimation of egocentric distances in the virtual relative to actual environment. This was confirmed. The authors used -2 diopter glasses to reduce the focal distance in the virtual environment. Overestimates were reduced by half. The authors conclude that calibration of perception is required for accurate feedforward reaching and that disparity matching is optimal visual information for calibration. <s> BIB002 </s> The Importance of Visual Attention in Improving the 3D-TV Viewing Experience: Overview and New Perspectives <s> A. Depth Cues: Combination and Conflicts <s> The idea of a largely segregated processing of color and form was initially supported by observations that geometric-optical illusions vanish under isoluminance. However, this finding is inconsistent with some psychophysical studies and also with physiological evidence showing that color and luminance are processed together by largely overlapping sets of neurons in the LGN, in V1, and in extrastriate areas. Here we examined the strength of nine geometric-optical illusions under isoluminance (Delboeuf, Ebbinghaus, Hering, Judd, Mul- ler-Lyer, Poggendorff, Ponzo, Vertical, Zollner). Subjects interactively manipulated computer-generated line drawings to counteract the illusory effect. In all cases, illusions presented under isoluminance (both for colors drawn from the cardinal LMo r S� (L + M) direc- tions of DKL color space) were as effective as the luminance versions (both for high and low contrast). The magnitudes of the illusion effects were highly correlated across subjects for the different conditions. In two additional experiments we determined that the strong illusions observed under isoluminance were not due to individual deviations from the photometric point of isoluminance or due to chro- matic aberrations. Our findings show that our conscious percept is affected similarly for both isoluminance and luminance conditions, suggesting that the joint processing for chromatic and luminance defined contours may extend well beyond early visual areas. � 2007 Elsevier Ltd. All rights reserved. <s> BIB003 </s> The Importance of Visual Attention in Improving the 3D-TV Viewing Experience: Overview and New Perspectives <s> A. Depth Cues: Combination and Conflicts <s> Cue combination rules have often been applied to the perception of surface shape but not to judgements of object location. Here, we used immersive virtual reality to explore the relationship between different cues to distance. Participants viewed a virtual scene and judged the change in distance of an object presented in two intervals, where the scene changed in size between intervals (by a factor of between 0.25 and 4). We measured thresholds for detecting a change in object distance when there were only ‘physical’ (stereo and motion parallax) or ‘texture-based’ cues (independent of the scale of the scene) and used these to predict biases in a distance matching task. Under a range of conditions, in which the viewing distance and position of the target relative to other objects was varied, the ratio of ‘physical’ to ‘texture-based’ thresholds was a good predictor of biases in the distance matching task. The cue combination approach, which successfully accounts for our data, relies on quite different principles from those underlying traditional models of 3D reconstruction. <s> BIB004
One of the major goals of 3D-TV is to increase the sensation of presence or immersion through the enhancement of depth perception. This is mainly achieved by changing the binocular disparity that is related to binocular depth cues. Nevertheless, fortunately for stereo-blind observers, our visual system perceives depth using several cues, which are not only limited to binocular ones. Monocular cues such as occlusion of objects, perspective information, relative and absolute size of objects, motion parallax, accommodation, texture gradient, direction of the light source, and shadows complement binocular cues. Depth cues have been analyzed and summarized concerning their accuracy and utility in BIB001 . All depth cues are fused together in an adaptive way depending on the viewing space conditions (personal, action, or vista space) but, to this date, only limited research has been done on the precedence, excitation and inhibition of the depth cues. In the Ponzo illusion it becomes evident that perspective provides a very strong depth cue, which supersedes for example the apparent size of known objects BIB003 . Studies on the relative importance of depth cues have also been conducted in the context of interactions with real-world objects in a virtual environment. Svarverud et al. have shown dependencies between stereoscopic disparity, motion parallax, and 2D-image based depth cues when locations of objects and distances are judged by humans in a virtual environment BIB004 . In some cases, adaptation is necessary as was shown for the case of accommodation by Bingham et al. BIB002 . When watching 3D content on currently available 3D-TV displays, depth cues might be in conflict. The strength of the conflict depends on the displayed content and in many cases the HVS can still correctly interpret the 3D scenario. One of the most apparent examples for this adaptation process is the switching of the views for the left and the right eye. While the binocular depth cues are opposite to all the other cues in this case, observers often report that they perceive stereoscopic 3D correctly. Nevertheless, after some time, they report visual discomfort, e.g., eye strain, headache or nausea. It might be assumed that the HVS is capable of performing a re-interpretation of the 3D depth cues but at a higher cognitive load. In general, enhancing the viewer's experience with binocular disparity might come as an additional workload on top of that required by monocular depth cues, especially if conflict is introduced. That is, a 3D-TV system might introduce cue conflicts that lead to visual discomfort. Considering that visual attention might be helpful in limiting some of those conflicting effects. With current 3D displays, accommodation is quite limited as it is forced to be fixed on the display plane itself. Consequently, the natural defocus depth cue is rather poor and exhibits possible conflicts with binocular disparity. Knowing how visual attention is deployed on a given content might be useful to reintroduce defocus blur, through adaptive blurring, and thus limiting depth cue conflicts. On the other hand, this is surely steering visual attention itself, which could be seen as a limitation on observers' freedom to explore content. As a matter of fact, driving visual attention introducing retinal blur (according to eccentricity) and defocus blur (according to depth) are candidate solutions to limit the cognitive load. In the next subsections, two other conflicts are detailed.