Inconsistency between the binocular and focus cues in stereoscopic augmented reality overburdens the visual system leading to its stress. However, a high individual variability of tolerance for visual stress makes it difficult to predict and generalize the user gain associated with the implementation of alternative visualization technologies. In this study, we investigated the relationship between the binocular function and perceptual judgments in augmented reality. We assessed the task completion time and accuracy of perceptual distance matching depending on the consistency of binocular and focus cues in the stereoscopic environment of augmented reality. The head-mounted display was driven in two modes: multifocal and monofocal mode, providing consistent-cues and inconsistent-cues condition, respectively. Participants matched the distance of a real object with images displayed at three viewing distances (concordant with distances of display focal planes in the consistent-cues condition). A thorough vision screening was performed before the experiment. As a result, individuals with low convergent fusional reserves and receded near point of convergence misjudged distances to a higher extent in comparison to others in the inconsistent-cues condition. In contrast, perceptual judgments were fast and less overestimated, as well as no significant effect of binocular function was revealed in the consistent-cues condition. We suggest that the binocular function measures characterizing individual tolerance for visual stress might be used as the predictors of user gain in the comparative assessment of new visualization technologies for the augmentation of reality.
KEYWORDS: Visualization, 3D volumetric display, 3D image processing, 3D displays, Optical components, 3D volumetric displays, Statistical analysis, Eye, Data analysis, Visual system
Three-dimensional images on multiple depth layers of the volumetric display provide the physiological depth cues which ensure the high precision of depth judgements at close viewing distances and enhance the user experience. However, the contribution of physiological cues declines with an increase of viewing distance (egocentric distance), and the human spatial perception varies depending on the inter-stimuli distance (exocentric distance). We conducted a psychophysical experiment to test the perception of three-dimensional images rendered on the volumetric display depending on exocentric and egocentric stimuli distance. The constant angular size visual stimuli were displayed on different depth layers of the optical element at three eccentricities in a random order. In 4AFC tasks, observers were required to indicate the closest stimulus. The decline in performance was evident at the largest tested exocentric distance, and it became more pronounced with an increase of egocentric distance. However, no performance differences manifested themselves when stimuli were located close to each other. Namely, the correct relative depth judgements were given quickly regardless of slight changes in the egocentric distance. We discuss how the viewing distance and spatial layout of stimuli facilitate perception of three-dimensional images on the volumetric display.
In natural viewing, numerous depth cues are available to the visual system, but their significance varies considerably depending on the viewing distance. How is it reflected in the outcome of depth judgements? We have designed a psychophysical experiment with a limited number of depth cues to examine distance-related changes in the correct response rate and time. Twenty young adults evaluated relative depth of stimuli in physical space. Each time four constant angular size achromatic stimuli were presented on a volumetric multi-planar display. One of these stimuli was demonstrated closer to the observer comparing to others. The experiment followed the four-interval forced-choice procedure. On any given trial, observers determined which one of four stimuli was located closest to them. The nine viewing distances ranged from 0.5 m to 2.5 m. Overall, the depth judgements were correct and fast at the close viewing distances. However, the correct response rate dropped markedly at 1.0 m distance and continued declining gradually at larger distances. The average response time experienced the linear growth with increasing distance. In total, we showed that the relative depth judgements based on binocular depth cues changed the most at the viewing distances that exceeded 1.0 m, as well as the response time and correctness were affected to varying degrees.
KEYWORDS: Visualization, Information visualization, Image segmentation, 3D volumetric displays, 3D volumetric display, 3D image processing, 3D displays, Visual information processing, Visual system
In diagnostics, radiologists search for anatomical abnormalities through generated three-dimensional data on flat displays. Professionals are required to scroll repeatedly through image stacks forth and back, as well as remember a broad amount of visual information. This process leads to working memory overload and decreased search outcome. In contrast, a volumetric multi-planar display includes many planes, which makes possible to visualize data in a true physical depth. Thus, theoretically, it can facilitate the visual search performance in diagnostics and lessen the necessity for repeated scrolling. Therefore, our work aims to explore practically the extent to which the visual search is effective, as well as deliver evidence on the scrolling strategy through image stacks when data are shown on many display planes. Visual search set consisted of constant angular size stimuli presented on ten out of twenty display planes in two depth segments. Participants searched for a target with varying target-distractor similarity within trials. All ten images were presented simultaneously in the beginning of each trial and participants scrolled freely through them. In the result, target discriminability affected significantly the correct response rate and time, as well as search behavior was consistent with the physical design of stimuli set. In more detail, the number of moves through image stack almost doubled when the target-distractor similarity increased and, overall, participants skipped searching repeatedly already seen images. The developed visual search task is suggested for implementation in studies of visual perception and search behavior in threedimensional displays.
KEYWORDS: Visualization, 3D volumetric displays, Medical imaging, 3D volumetric display, 3D acquisition, Visual system, Image quality, 3D image processing, 3D displays, New and emerging technologies
In medical imaging, large sets of two-dimensional images are used for evaluating anatomical structures. Observers experience high cognitive load due to necessity of memorizing information and data is not seen in a real volume. A volumetric multi-planar display is a promising technology that can eliminate above mentioned issues by producing images in a real three-dimensional space. Therefore, the goal of our study was to investigate how well individuals perceived a difference in spatial localization of visual stimuli and describe its impact on visual search performance in three-dimensional digital space. Participants searched for a target stimulus which was located closer to the observer comparing to other stimuli in different depth segments of a display and provided subjective evaluation of the task difficulty. The results revealed that on average visual attention could be deployed without significant differences on all four depths segments in terms of response time and quality. But at the same time, eccentricity of stimuli influenced considerably the performance which can be related to higher cognitive load due to limitation of visual acuity and attention in the peripheral visual field. To be added, subjective evaluation of perceived task difficulty matched well response time and accuracy in visual search. The obtained results leaded to the conclusion that spatial layout of stimuli in horizontal and vertical dimension had a bigger impact on visual search performance comparing to the third dimension on a volumetric multi-planar display.
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