Cross Reality (CR) is a new emerging field based on the current developments in Mixed Reality hardware, especially supported by the broad market penetration of video-based see-through Head-Mounted Displays. It refers to applications that span across different stages (real, Augmented Reality, Augmented Virtuality, Virtual Reality) of the reality-virtuality continuum, where users are interconnected between different stages and/or are able to transition between these stages. This publication follows the concept of other grand challenges publications and reflects the discussion of various researchers invested in CR. After an initial discussion at the 1stJoint Workshop on Cross Reality at IEEE ISMAR 2023, six topic groups have been identified, leading to 22 challenges, which were discussed in groups over the period of multiple months. The discussion of these challenges should act as a road map for future research in the area of CR.

We investigate hybrid user interfaces (HUIs), aiming to establish a cohesive understanding and to adopt consistent terminology for this nascent research area. HUIs combine heterogeneous devices in complementary roles, leveraging the distinct benefits of each. Our work focuses on cross-device interaction between 2D devices and mixed reality environments, which are particularly compelling, leveraging the familiarity of traditional 2D platforms while providing spatial awareness and immersion. Although prior work has prominently explored such HUIs in the context of mixed reality, we still lack a cohesive understanding of the unique design possibilities and challenges of such combinations, resulting in a fragmented research landscape. We conducted a systematic survey and present a taxonomy of HUIs that combine conventional display technology and mixed reality environments. Based on this, we discuss past and current challenges, the evolution of definitions, and prospective opportunities to tie together the past 30 years of research with our vision of future HUIs.

We introduce the SpatialMouse, a hybrid pointing device that combines the capabilities of a desktop mouse with the spatial input of a virtual reality (VR) controller, enabling seamless transitions between 2D and 3D interaction spaces in immersive mixed reality environments. Holistic usage scenarios in mixed reality involve tasks suited alternately to 2D or 3D information spaces. Yet, existing input devices excel in either 2D or 3D, but not both, making it necessary to switch between multiple input devices (e.g., mouse and VR controller). Our SpatialMouse addresses this issue, offering the affordances of a desktop mouse for indirect 2D pointing and the spatial capabilities of VR controllers with six degrees of freedom. In a user study with 12 participants, our prototype significantly reduced perceived task load and improved user experience compared to switching between separate devices. We extract design recommendations to further support such hybrid input approaches.

Supporting remote collaboration through augmented reality facilitates the experience of co-presence by presenting the collaborator’s avatar in the user’s physical environment. While visual user representations are continuously researched and advanced, the audio configuration – especially in combination with different visualizations – is rarely considered. In a user study (n = 48, 24 dyads), we evaluate the combination of two visual (Simple vs. Rich Avatar) with two auditory (Mono vs. Spatial Audio) user representations, to investigate their impact on user’s overall experience, performance, and perceived social presence during collaboration. Our results show a preference for rich auditory and visual user representations, as Spatial Audio supports completion of parallel tasks and the Rich Avatar positively influence user experience. However, the Simple Avatar draws less attention, which potentially benefits task efficiency, advocating for simpler visualizations in performance-oriented settings. Our findings contribute to a deeper understanding of how visual and auditory user representation combinations impact remote collaboration in augmented reality.

Smartphones conveniently place large information spaces in the palms of our hands. While research has shown that larger screens positively affect spatial memory, workload, and user experience, smartphones remain fairly compact for the sake of device ergonomics and portability. Thus, we investigate the use of hybrid user interfaces to virtually increase the available display size by complementing the smartphone with an augmented reality head-worn display. We thereby combine the benefits of familiar touch interaction with the near-infinite visual display space afforded by augmented reality. To better understand the potential of virtually-extended displays and the possible issues of splitting the user’s visual attention between two screens (real and virtual), we conducted a within-subjects experiment with 24 participants completing navigation tasks using different virtually-augmented display sizes. Our findings reveal that a desktop monitor size represents a “sweet spot” for extending smartphones with augmented reality, informing the design of hybrid user interfaces.

In image quality assessment, a collective visual quality score for an image or video is obtained from the individual ratings of many subjects. One commonly used format for these experiments is the two-alternative forced choice method. Two stimuli with the same content but differing visual quality are presented sequentially or side-by-side. Subjects are asked to select the one of better quality, and when uncertain, they are required to guess. The relaxed alternative forced choice format aims to reduce the cognitive load and the noise in the responses due to the guessing by providing a third response option, namely, “not sure”. This work presents a large and comprehensive crowdsourcing experiment to compare these two response formats: the one with the “not sure” option and the one without it. To provide unambiguous ground truth for quality evaluation, subjects were shown pairs of images with differing numbers of dots and asked each time to choose the one with more dots. Our crowdsourcing study involved 254 participants and was conducted using a within-subject design. Each participant was asked to respond to 40 pair comparisons with and without the “not sure” response option and completed a questionnaire to evaluate their cognitive load for each testing condition. The experimental results show that the inclusion of the “not sure” response option in the forced choice method reduced mental load and led to models with better data fit and correspondence to ground truth. We also tested for the equivalence of the models and found that they were different. The dataset is available at http://database.mmsp-kn.de/cogvqa-database.html.

The nascent field of mixed reality is seeing an ever-increasing need for user studies and field evaluation, which are particularly challenging given device heterogeneity, diversity of use, and mobile deployment. Immersive analytics tools have recently emerged to support such analysis in situ, yet the complexity of the data also warrants an ex-situ analysis using more traditional non-immersive visual analytics setups. To bridge the gap between both approaches, we introduce ReLive: a mixed-immersion visual analytics framework for exploring and analyzing mixed reality user studies. ReLive combines an in-situ virtual reality view with a complementary ex-situ desktop view. While the virtual reality view allows users to relive interactive spatial recordings replicating the original study, the synchronized desktop view provides a familiar interface for analyzing aggregated data. We validated our concepts in a two-step evaluation consisting of a design walkthrough and an empirical expert user study.

Augmented reality (AR) can create the illusion of being virtually co-located during remote collaboration, e.g., by visualizing remote co-workers as avatars. However, spatial awareness of each other's activities is limited as physical spaces, including the position of physical devices, are often incongruent. Therefore, alignment methods are needed to support activities on physical devices. In this paper, we present the concept of Re-locations, a method for enabling remote collaboration with augmented reality in incongruent spaces. The idea of the concept is to enrich remote collaboration activities on multiple physical devices with attributes of co-located collaboration such as spatial awareness and spatial referencing by locally relocating remote user representations to user-defined workspaces. We evaluated the Re-locations concept in an explorative user study with dyads using an authentic, collaborative task. Our findings indicate that Re-locations introduce attributes of co-located collaboration like spatial awareness and social presence. Based on our findings, we provide implications for future research and design of remote collaboration systems using AR.

Recent research in the area of immersive analytics demonstrated the utility of head-mounted augmented reality devices for visual data analysis. However, it can be challenging to use the by default supported mid-air gestures to interact with visualizations in augmented reality (e.g. due to limited precision). Touch-based interaction (e.g. via mobile devices) can compensate for these drawbacks, but is limited to two-dimensional input. In this work we present STREAM: Spatially-aware Tablets combined with Augmented Reality Head-Mounted Displays for the multimodal interaction with 3D visualizations. We developed a novel eyes-free interaction concept for the seamless transition between the tablet and the augmented reality environment. A user study reveals that participants appreciated the novel interaction concept, indicating the potential for spatially-aware tablets in augmented reality. Based on our findings, we provide design insights to foster the application of spatially-aware touch devices in augmented reality and research implications indicating areas that need further investigation.

Augmented Reality (AR) supported collaboration is a popular topic in HCI research. Previous work has shown the benefits of collaborative 3D object manipulation and identified two possibilities: Either separate or compose users’ inputs. However, their experimental comparison using handheld AR displays is still missing. We, therefore, conducted an experiment in which we tasked 24 dyads with collaboratively positioning virtual objects in handheld AR using three manipulation techniques: 1) Separation – performing only different manipulation tasks (i. e., translation or rotation) simultaneously, 2) Composition – performing only the same manipulation tasks simultaneously and combining individual inputs using a merge policy, and 3) Hybrid – performing any manipulation tasks simultaneously, enabling dynamic transitions between Separation and Composition. While all techniques were similarly effective, Composition was least efficient, with higher subjective workload and worse user experience. Preferences were polarized between clear work division (Separation) and freedom of action (Hybrid). Based on our findings, we offer research and design implications.

Cross-device interaction with tablets is a popular topic in HCI research. Recent work has shown the benefits of including multiple devices into users' workflows while various interaction techniques allow transferring content across devices. However, users are only reluctantly using multiple devices in combination. At the same time, research on cross-device interaction struggles to find a frame of reference to compare techniques or systems. In this paper, we try to address these challenges by studying the interplay of interaction techniques, device utilization, and task-specific activities in a user study with 24 participants from different but complementary angles of evaluation using an abstract task, a sensemaking task, and three interaction techniques. We found that different interaction techniques have a lower influence than expected, that work behaviors and device utilization depend on the task at hand, and that participants value specific aspects of cross-device interaction.

Programming assignments in computer science courses are often processed in pairs or groups of students. While working together, students face several shortcomings in today's software: The lack of real-time collaboration capabilities, the setup time of the development environment, and the use of different devices or operating systems can hamper students when working together on assignments. Text processing platforms like Google Docs solve these problems for the writing process of prose text, and computational notebooks like Google Colaboratory for data analysis tasks. However, none of these platforms allows users to implement interactive applications. We deployed a web-based literate programming system for three months during an introductory course on application development to explore how collaborative programming practices unfold and how the structure of computational notebooks affect the development. During the course, pairs of students solved weekly programming assignments. We analyzed data from weekly questionnaires, three focus groups with students and teaching assistants, and keystroke-level log data to facilitate the understanding of the subtleties of collaborative programming with computational notebooks. Findings reveal that there are distinct collaboration patterns; the preferred collaboration pattern varied between pairs and even varied within pairs over the course of three months. Recognizing these distinct collaboration patterns can help to design future computational notebooks for collaborative programming assignments.

Building data analysis skills is part of modern elementary school curricula. Recent research has explored how to facilitate children's understanding of visual data representations through completion exercises which highlight links between concrete and abstract mappings. This approach scaffolds visualization activities by presenting a target visualization to children. But how can we engage children in more free-form visual data mapping exercises that are driven by their own mapping ideas? How can we scaffold a creative exploration of visualization techniques and mapping possibilities? We present Construct-A-Vis, a tablet-based tool designed to explore the feasibility of free-form and constructive visualization activities with elementary school children. Construct-A-Vis provides adjustable levels of scaffolding visual mapping processes. It can be used by children individually or as part of collaborative activities. Findings from a study with elementary school children using Construct-A-Vis individually and in pairs highlight the potential of this free-form constructive approach, as visible in children's diverse visualization outcomes and their critical engagement with the data and mapping processes. Based on our study findings we contribute insights into the design of free-form visualization tools for children, including the role of tool-based scaffolding mechanisms and shared interactions to guide visualization activities with children.

Analysing and understanding brain function and disorder is the main focus of neuroscience. Due to the high complexity of the brain, directionality of the signal and changing activity over time, visual exploration and data analysis are difficult. For this reason, a vast amount of research challenges are still unsolved. We explored different challenges of the visual analysis of brain data and the design of corresponding immersive environments in collaboration with experts from the biomedical domain. We built a prototype of an immersive virtual reality environment to explore the design space and to investigate how brain data analysis can be supported by a variety of design choices. Our environment can be used to study the effect of different visualisations and combinations of brain data representation, as for example network layouts, anatomical mapping or time series. As a long-term goal, we aim to aid neuro-scientists in a better understanding of brain function and disorder.

People's ability to remember and recall spatial information can be harnessed to improve navigation and search performances in interactive systems. In this paper, we investigate how display size and input modality influence spatial memory, especially in relation to efficiency and user satisfaction. Based on an experiment with 28 participants, we analyze the effect of three input modalities (trackpad, direct touch, and gesture-based motion controller) and two display sizes (10.6" and 55") on people's ability to navigate to spatially spread items and recall their positions. Our findings show that the impact of input modality and display size on spatial memory is not straightforward, but characterized by trade-offs between spatial memory, efficiency, and user satisfaction.

In recent years, research on cross-device interaction has become a popular topic in HCI leading to novel interaction techniques mutually interfering with new evolving theoretical paradigms. Building on previous research, we implemented an individual multi-device work environment for creative activities. In a study with 20 participants, we compared a traditional toolbar-based condition with two conditions facilitating spatially distributed tools on digital panels and on physical devices. We analyze participants' interactions with the tools, encountered problems and corresponding solutions, as well as subjective task load and user experience. Our findings show that the spatial distribution of tools indeed offers advantages, but also elicits new problems, that can partly be leveraged by the physical affordances of mobile devices.

Cross-device collaboration with tablets is an increasingly popular topic in HCI. Previous work has shown that tablet-only collaboration can be improved by an additional shared workspace on an interactive tabletop. However, large tabletops are costly and need space, raising the question to what extent the physical size of shared horizontal surfaces really pays off. In order to analyse the suitability of smaller-than-tabletop devices (e.g. tablets) as a low-cost alternative, we studied the effect of the size of a shared horizontal interactive workspace on users' attention, awareness, and efficiency during cross-device collaboration. In our study, 15 groups of two users executed a sensemaking task with two personal tablets (9.7") and a horizontal shared display of varying sizes (10.6", 27", and 55"). Our findings show that different sizes lead to differences in participants' interaction with the tabletop and in the groups' communication styles. To our own surprise we found that larger tabletops do not necessarily improve collaboration or sensemaking results, because they can divert users' attention away from their collaborators and towards the shared display.