▶ Addresses the accessibility, usability, and, ultimately, acceptability of Information Society Technologies by anyone, anywhere, at anytime, and through any media and device. ▶ Focuses on theoretical, methodological, and empirical research, of both technological and non-technological nature. ▶ Features papers that report on theories, methods, tools, empirical results, reviews, case studies, and best-practice examples.

Universal access in the information society

The vergence-accommodation conflict (VAC) remains a major problem in head-mounted displays for virtual and augmented reality (VR and AR). In this review, I discuss why this problem is pivotal for nearby tasks in VR and AR, present a comprehensive taxonomy of potential solutions, address advantages and shortfalls of each design, and cover various ways to better evaluate the solutions. The review describes how VAC is addressed in monocular, stereoscopic, and multiscopic HMDs, including retinal scanning and accommodation-free displays. Eye-tracking-based approaches that do not provide natural focal cues—gaze-guided blur and dynamic stereoscopy—are also covered. Promising future research directions in this area are identified.

Resolving the Vergence-Accommodation Conflict in Head-Mounted Displays

A myriad of design rules for what constitutes a “good” colormap can be found in the literature. Some common rules include order, uniformity, and high discriminative power. However, the meaning of many of these terms is often ambiguous or open to interpretation. At times, different authors may use the same term to describe different concepts or the same rule is described by varying nomenclature. These ambiguities stand in the way of collaborative work, the design of experiments to assess the characteristics of colormaps, and automated colormap generation. In this paper, we review current and historical guidelines for colormap design. We propose a specified taxonomy and provide unambiguous mathematical definitions for the most common design rules.

The Good, the Bad, and the Ugly: A Theoretical Framework for the Assessment of Continuous Colormaps

This survey provides an overview of perceptually motivated techniques for the visualization of medical image data, including physics-based lighting techniques as well as illustrative rendering that incorporate spatial depth and shape cues. Additionally, we discuss evaluations that were conducted in order to study the perceptual effects of these visualization techniques as compared to conventional techniques. These evaluations assessed depth and shape perception with depth judgment, orientation matching, and related tasks. This overview of existing techniques and their evaluation serves as a basis for defining the evaluation process of medical visualizations and to discuss a research agenda.

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A survey of perceptually motivated 3D visualization of medical image data

We report on an experiment testing gaze-contingent depth-of-field (DOF) for the reduction of visual discomfort when viewing stereoscopic displays. Subjective results are compelling, showing, we believe for the first time, that gaze-contingent depth-of-field significantly reduces visual discomfort. When individual stereoacuity is taken into account, objective measurements of gaze vergence corroborate previous reports, showing significant bias toward the zero depth plane, where error is smallest. As with earlier similar attempts, participants expressed a dislike toward gaze-contingent DOF. Although not statistically significant, this dislike is likely attributed to the eye tracker's spatial inaccuracy as well as the DOF simulation's noticeable temporal lag.

Reducing visual discomfort of 3D stereoscopic displays with gaze-contingent depth-of-field

Focus-context techniques provide visual guidance in visualizations by giving strong visual prominence to elements of interest while the context is suppressed. However, finding a visual feature to enhance for the focus to pop out from its context in a large dynamic scene, while leading to minimal visual deformation and subjective disturbance, is challenging. This paper proposes Attractive Flicker, a novel technique for visual guidance in dynamic narrative visualizations. We first show that flicker is a strong visual attractor in the entire visual field, without distorting, suppressing, or adding any scene elements. The novel aspect of our Attractive Flicker technique is that it consists of two signal stages: The first “orientation stage” is a short but intensive flicker stimulus to attract the attention to elements of interest. Subsequently, the intensive flicker is reduced to a minimally disturbing luminance oscillation (“engagement stage”) as visual support to keep track of the focus elements. To find a good trade-off between attraction effectiveness and subjective annoyance caused by flicker, we conducted two perceptual studies to find suitable signal parameters. We showcase Attractive Flicker with the parameters obtained from the perceptual statistics in a study of molecular interactions. With Attractive Flicker, users were able to easily follow the narrative of the visualization on a large display, while the flickering of focus elements was not disturbing when observing the context.

Attractive Flicker — Guiding Attention in Dynamic Narrative Visualizations

In the design of interactive applications, notably games, a recent trend is to understand player behavior by investigating telemetry logs as is the focus of many chapters in this book or by integrating the use of psychophysics as is the subject of Chaps. 26 and 27. In addition to these valuable methods, measuring, where players are likely to focus, could be a very useful tool in the arsenal of game designers. This knowledge can be utilized to help game designers decide how and where to allocate computing resources, such as rendering and various kinds of simulations of physical properties. This leaves as many computing cycles as possible free to carry out other tasks. Therefore, the perceived realism of a game can be increased by perceptually optimizing calculations that are computationally intensive, including physically based lighting (e.g. ray-tracing Cater et al. 2003), animations (e.g. crowds of characters McDonnell et al. 2009), physically correct simulations of the interaction of materials (e.g. collision detection (O’Sullivan 2005), natural behavior of clothes or fluids etc.). Level of Detail variants of simulation or rendering techniques can be used in regions which are less attended by the player, while accurate simulations can be used within the expected focus of a user. Verifying or improving game mechanics and AI could be other uses.

Visual Attention and Gaze Behavior in Games: An Object-Based Approach

With the emergence of affordable 3D displays, stereoscopy is becoming a commodity. However, often users report discomfort even after brief exposures to stereo content. One of the main reasons is the conflict between vergence and accommodation that is caused by 3D displays. We investigate dynamic adjustment of stereo parameters in a scene using gaze data in order to reduce discomfort. In a user study, we measured stereo fusion times after abrupt manipulation of disparities using gaze data. We found that gaze-controlled manipulation of disparities can lower fusion times for large disparities. In addition we found that gaze-controlled disparity adjustment should be applied in a personalized manner and ideally performed only at the extremities or outside the comfort zone of subjects. These results provide important insight on the problems associated with fast disparity manipulation and are essential for developing appealing gaze-contingent and gaze-controlled applications.

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The effects of fast disparity adjustment in gaze-controlled stereoscopic applications

Gaze analysis and prediction in interactive virtual environments, such as games, is a challenging topic since the 3D perspective and variations of the viewpoint as well as the current task introduce many variables that affect the distribution of gaze. In this article, we present a novel pipeline to study eye-tracking data acquired from interactive 3D applications. The result of the pipeline is an importance map which scores the amount of gaze spent on each object. This importance map is then used as a heuristic to predict a user's visual attention according to the object properties present at runtime. The novelty of this approach is that the analysis is performed in object space and the importance map is defined in the feature space of high-level properties. High-level properties are used to encode task relevance and other attributes, such as eccentricity, which may have an impact on gaze behavior.The pipeline has been tested with an exemplary study on a first-person shooter game. In particular, a protocol is presented describing the data acquisition procedure, the learning of different importance maps from the data, and finally an evaluation of the performance of the derived gaze predictors. A metric measuring the degree of correlation between attention predicted by the importance map and the actual gaze yielded clearly positive results. The correlation becomes particularly strong when the player is attentive to an in-game task.

An empirical pipeline to derive gaze prediction heuristics for 3D action games

Stimuli obtained from highly dynamic 3D virtual environments and synchronous eye-tracking data are commonly used by algorithms that strive to correlate gaze to scene objects, a process referred to as gaze-to-object mapping (GTOM). We propose to address this problem with a probabilistic approach using Bayesian inference. The desired result of the inference is a predicted probability density function (PDF) specifying for each object in the scene a probability to be attended by the user. To evaluate the quality of a predicted attention PDF, we present a methodology to assess the information value (i.e., likelihood) in the predictions of different approaches that can be used to infer object attention. To this end, we propose an experiment based on a visual search task, which allows us to determine the object of attention at a certain point in time under controlled conditions. We perform this experiment with a wide range of static and dynamic visual scenes to obtain a ground-truth evaluation dataset, allowing us to assess GTOM techniques in a set of 30 particularly challenging cases.

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Matthias Bernhard

Papers

Attractive Flicker — Guiding Attention in Dynamic Narrative Visualizations

Visual Attention and Gaze Behavior in Games: An Object-Based Approach

The effects of fast disparity adjustment in gaze-controlled stereoscopic applications

An empirical pipeline to derive gaze prediction heuristics for 3D action games

Gaze-to-Object Mapping during Visual Search in 3D Virtual Environments