Eco-friendly service options (EFSOs) aim to reduce personal carbon emissions, yet their eco-friendly framing may permit increased consumption, weakening their intended impact. Such rebound effects remain underexamined in HCI, including how common eco-feedback approaches shape them. We investigate this in an online within-subjects experiment (N = 75) in a ride-hailing context. Participants completed 10 trials for five conditions (No EFSO, EFSO - Minimal, EFSO - CO2 Equivalency, EFSO - Gamified, EFSO - Social), yielding 50 choices between walking and ride-hailing for trips ranging from 0.5mi–2.0mi (≈ 0.80km-3.22km). We measured how different EFSO variants affected ride-hailing uptake relative to a No EFSO baseline. EFSOs lacking explicit eco-feedback metrics increased ride-hailing uptake, and qualitative responses indicate that EFSOs can make convenience-driven choices more permissible. We conclude with implications for designing EFSOs that begin to take rebound effects into account.

Presence is an important and widely used metric to measure the quality of virtual reality (VR) applications. Given the multifaceted and subjective nature of presence, the most common measures for presence are questionnaires. But there is little research on their validity regarding specific presence dimensions and their responsiveness to differences in perception among users. We investigated four presence questionnaires (SUS, PQ, IPQ, Bouchard) on their responsiveness to intensity variations of known presence dimensions and asked users about their consistency with their experience. Therefore, we created five VR scenarios that were designed to emphasize a specific presence dimension. Our findings showed heterogeneous sensitivity of the questionnaires dependent on the different dimensions of presence. This highlights a context-specific suitability of presence questionnaires. The questionnaires' sensitivity was further stated as lower than actually perceived. Based on our findings, we offer guidance on selecting these questionnaires based on their suitability for particular use cases.

Infinite scrolling on social media platforms is designed to encourage prolonged engagement, leading users to spend more time than desired, which can provoke negative emotions. Interventions to mitigate infinite scrolling have shown initial success, yet users become desensitized due to the lack of contextual relevance. Understanding how contextual factors influence intervention effectiveness remains underexplored. We conducted a 7-day user study (N=72) investigating how these contextual factors affect users' reactance and responsiveness to interventions during infinite scrolling. Our study revealed an interplay, with contextual factors such as being at home, sleepiness, and valence playing significant roles in the intervention's effectiveness. Low valence coupled with being at home slows down the responsiveness to interventions, and sleepiness lowers reactance towards interventions, increasing user acceptance of the intervention. Overall, our work contributes to a deeper understanding of user responses toward interventions and paves the way for developing more effective interventions during infinite scrolling.

The introduction of Highly Automated Vehicles (HAVs) has the potential to increase the independence of blind and visually impaired people (BVIPs). However, ensuring safety and situation awareness when exiting these vehicles in unfamiliar environments remains challenging. To address this, we conducted an interactive workshop with N=5 BVIPs to identify their information needs when exiting an HAV and evaluated three prior-developed low-fidelity prototypes. The insights from this workshop guided the development of PathFinder, a multimodal interface combining visual, auditory, and tactile modalities tailored to BVIP's unique needs. In a three-factorial within-between-subject study with N=16 BVIPs, we evaluated PathFinder against an auditory-only baseline in urban and rural scenarios. PathFinder significantly reduced mental demand and maintained high perceived safety in both scenarios, while the auditory baseline led to lower perceived safety in the urban scenario compared to the rural one. Qualitative feedback further supported PathFinder's effectiveness in providing spatial orientation during exiting.

Mixed Reality (MR) integrates virtual objects with the real world, offering potential but raising concerns about misuse through dark patterns. This study explored the effects of four dark patterns, adapted from prior research, and applied to MR across three targets: places, products, and people. In a two-factorial within-subject study with 74 participants, we analyzed 13 videos simulating MR experiences during a city walk. Results show that all dark patterns significantly reduced user comfort, increased reactance, and decreased the intention to use MR glasses, with the most disruptive effects linked to personal or monetary manipulation. Additionally, the dark patterns of Emotional and Sensory Manipulation and Hiding Information produced similar impacts on the user in MR, suggesting a re-evaluation of current classifications to go beyond deceptive design techniques. Our findings highlight the importance of developing ethical design guidelines and tools to detect and prevent dark patterns as immersive technologies continue to evolve.

Redirected walking (RDW) is a technique that allows users to navigate larger physical spaces in virtual reality (VR) environments by manipulating the users’ view of the virtual world. In this study, we investigate the effect of adding spatial audio elements to curvature gains in RDW aiming to increase the perceptual threshold for the manipulation and allowing for higher levels of unnoticed redirection. We conducted a user study (n = 18), evaluating perceptual thresholds across conditions with and without spatial audio elements across different curvature gains. We found that spatial audio can significantly increase thresholds with a large effect size. This finding indicates the value of spatial audio for RDW. It could facilitate higher levels of redirection, while maintaining a convincing experience, leading to more freedom to navigate virtual environments in even smaller physical spaces.

Object manipulation in 3D space, meaning translating, rotating, and scaling, is ubiquitous in virtual reality (VR), and several interaction techniques have been developed in the past to optimize the task performance and usability. However, preliminary research indicates that individual spatial abilities also have an impact. Yet, it was never investigated if users’ spatial abilities influence VR object manipulation. We assessed this in a user study (N=66) using 21 manipulation tasks defined in a Fitts’ law-related approach. As interaction techniques, we chose gizmos for simultaneously manipulating 1 and 3 degrees of freedom (DOF) and a handle bar metaphor for 7 DOF. Higher spatial abilities resulted in significantly shorter task completion time and more targeted manipulations, while task accuracy was unaffected. However, an optimized interaction technique could compensate individual disadvantages. We propose seven guidelines on spatial abilities in interaction technique design and research to personalize and improve VR applications.

Pair-learning is beneficial for learning outcome, motivation, and social presence, and so is virtual reality (VR) by increasing immersion, engagement, motivation, and interest of students. Nevertheless, there is a research gap if the benefits of pair-learning and VR can be combined. Furthermore, it is not clear which influence it has if only one or both peers use VR. To investigate these aspects, we implemented two types of VR pair-learning systems, a symmetric system with both peers using VR and an asymmetric system with one using a tablet. In a user study (N=46), the symmetric system statistically significantly provided higher presence, immersion, player experience, and lower intrinsic cognitive load, which are all important for learning. Symmetric and asymmetric systems performed equally well regarding learning outcome, highlighting that both are valuable learning systems. We used these findings to define guidelines on how to design co-located VR pair-learning applications, including characteristics for symmetric and asymmetric systems.

Voice assistants (VAs) are present in homes, smartphones, and cars. They allow users to perform tasks without graphical or tactile user interfaces, as they are designed for natural language interaction. However, we found that currently, VAs are emulating human behavior by responding in complete sentences, limiting the design options, and preventing VAs from meeting their full potential as a utilitarian tool. We implemented a VA that handles requests in three response styles: two differing short keyword-based response styles and a full-sentence baseline. In a user study, 72 participants interacted with our VA by issuing eight requests. Results show that the short responses were perceived similarly useful and likable while being perceived as more efficient, especially for commands, and sometimes better to comprehend than the baseline. To achieve widespread adoption, we argue that VAs should be customizable and adapt to users instead of always responding in full sentences.

Players can get stuck in video games, which impedes their process to their goal and results in unfavorable outcomes like negative emotions, impediments of flow, and obstacles for learning. Currently, it is not easily possible to assess if a player is stuck, as no widely accepted definition of "being stuck" in games exists. We conducted 13 expert interviews and a systematic literature review with 104 relevant papers selected from 4022 candidates. We present a definition of "being stuck" that conceptualizes the state as a continuum and contextualize it within related concepts. Our stuck continuum can be applied to regulate the player's stuck level. We propose a taxonomy of measures that are useful for the detection of the level of stuckness and discuss the effectiveness of countermeasures. Our stuck concept is crucial for game developers creating an optimal player experience in games.

Many people utilize audio equipment to escape from noises around them, leading to the desired isolation but also dangerously reduced awareness. Mediation of sounds through smarter headphones (e.g., hearables) could address this by providing non-uniform interaction with sounds while retaining a comfortable, yet informative soundscape. In a week-long event sampling study (n = 12), we found that users mostly desire muting or a distinct "quiet-but-audible" volume for sound sources. A follow-up study (n = 12) compared a reduced interaction granularity with a continuous one in VR. Usability and workload did not differ significantly for the two granularities but a set of four states can be considered sufficient for most scenarios, namely: ''muted'', ''quieter'', ''louder'' and ''unchanged'', allowing for smoother interaction flows. We provide implications for the design of interactive auditory mediated reality systems enabling users to be safe, comfortable and less isolated from their surroundings, while re-gaining agency over their sense of hearing.

Natural navigation in VR is challenging due to spatial limitations. While Teleportation enables navigation within very small physical spaces and without causing motion sickness symptoms, it may reduce the feeling of presence and spacial awareness. Redirected walking (RDW), in contrast, allows users to naturally walk while staying inside a finite, but still very large, physical space. We present Telewalk, a novel locomotion approach that combines curvature and translation gains known from RDW research in a perceivable way. This combination enables Telewalk to be applied even within a physical space of 3m x 3m. Utilizing the head rotation as input device enables directional changes without any physical turns to keep the user always on an optimal circular path inside the real world while freely walking inside the virtual one. In a user study we found that even though motion sickness susceptible participants reported respective symptoms, Telewalk did result in stronger feelings of presence and immersion and was seen as more natural then Teleportation.

Natural haptic feedback in virtual reality (VR) is complex andchallenging, due to the intricacy of necessary stimuli and re-spective hardware. Pseudo-haptic feedback aims at providinghaptic feedback without providing actual haptic stimuli butby using other sensory channels (e.g. visual cues) for feed-back. We combine such an approach with the additional inputmodality of muscle activity that is mapped to a virtual force toinfluence the interaction flow.

While the real world provides humans with a huge variety of sensory stimuli, virtual worlds most of all communicate their properties by visual and auditory feedback due to the design of current head mounted displays (HMDs). Since HMDs offer sufficient contact area to integrate additional actuators, prior works utilised a limited amount of haptic actuators to integrate respective information about the virtual world. With the Face/On prototype complex feedback patterns are introduced that combine a high number of vibration motors with additional thermal sources to transport multi-modal and spatial information. A pre-study determining the boundaries of the feedbacks' intensities as well as a user study showing a significant increase of presence and enjoyment validate Face/On's approach.

Current approaches for locomotion in virtual reality are either creating a visual-vestibular conflict, which is assumed to cause simulator sickness, or use metaphors such as teleportation to travel longer distances, lacking the perception of self motion. We propose VRSpinning, a seated locomotion approach based around stimulating the user's vestibular system using a rotational impulse to induce the perception of linear self-motion. In a first study we explored the approach of oscillating the chair in different frequencies during visual forward motion and collected user preferences on applying these feedback types. In a second user study we used short bursts of rotational acceleration to match the visual forward acceleration. We found that this rotational stimulus significantly reduced simulator sickness and increased the perception of self-motion in comparison to no physical motion.

Including haptic feedback in current consumer VR applications is frequently challenging, since technical possibilities to create haptic feedback in consumer-grade VR are limited. While most systems include and make use of the possibility to create tactile feedback through vibration, kinesthetic feedback systems almost exclusively rely on external mechanical hardware to induce actual sensations so far. In this paper, we describe an approach to create a feeling of such sensations by using unmodified off-the-shelf hardware and a software solution for a multi-modal pseudo-haptics approach. We first explore this design space by applying user-elicited methods, and afterwards evaluate our refined solution in a user study. The results show that it is indeed possible to communicate kinesthetic feedback by visual and tactile cues only and even induce its perception. While visual clipping was generally unappreciated, our approach led to significant increases of enjoyment and presence.

Virtual reality (VR) technology strives to enable a highly immersive experience for the user by including a wide variety of modalities (e.g. visuals, haptics). Current VR hardware however lacks a sufficient way of communicating the perception of weight of an object, resulting in scenarios where users can not distinguish between lifting a bowling ball or a feather. We propose a solely software based approach of simulating weight in VR by deliberately using perceivable tracking offsets. These tracking offsets nudge users to lift their arm higher and result in a visual and haptic perception of weight. We conducted two user studies showing that participants intuitively associated them with the sensation of weight and accept them as part of the virtual world. We further show that compared to no weight simulation, our approach led to significantly higher levels of presence, immersion and enjoyment. Finally, we report perceptional thresholds and offset boundaries as design guidelines for practitioners.

Redirected walking (RDW) allows virtual reality (VR) users to walk infinitely while staying inside a finite physical space through subtle shifts (gains) of the scene to redirect them back inside the volume. All prior approaches measure the feasibility of RDW techniques based on if the user perceives the manipulation, leading to rather small applicable gains. However, we treat RDW as an interaction technique and therefore use visually perceivable gains instead of using the perception of manipulation. We revisited prior experiments with focus on applied gains and additionally tested higher gains on the basis of applicability in a user study. We found that users accept curvature gains up to 20°/m, which reduces the necessary physical volume down to approximately 6x6m for virtually walking infinitely straight ahead. Our findings strife to rethink the usage of redirection from being unperceived to being applicable and natural.

We perceive the flow of time as a constant factor in the real world, but there are examples in media, like films or games, where time is being manipulated and slowed down. Manipulating temporal cues is simple in linear media by slowing down video and audio. Interactive media like VR however poses additional challenges, because user interaction speed is independent from media speed. While the speed of the environment can still be manipulated easily, interaction is a new aspect to consider. We implemented such manipulation by slowing down visual feedback of user movements. In prior experiments we slowed down the virtual representation of a user by applying a velocity based low pass filter and by visually redirecting the motion. We found such a manipulation to be even contributing to realism, enjoyment or presence as long as it is consistent with the experience.

The integration of multi-sensory stimuli, e.g. haptic airflow, in virtual reality (VR) has become an important topic of VR research and proved to enhance the feeling of presence. VaiR focuses on an accurate and realistic airflow simulation that goes far beyond wind. While previous works on the topic of airflow in VR are restricted to wind, while focusing on the feeling of presence, there is to the best of our knowledge no work considering the conceptual background or on the various application areas. Our pneumatic prototype emits short and long term flows with a minimum delay and is able to animate wind sources in 3D space around the user's head. To get insights on how airflow can be used in VR and how such a device should be designed, we arranged focus groups and discussed the topic. Based on the gathered knowledge, we developed a prototype which proved to increase presence, as well as enjoyment and realism, while not disturbing the VR experience.

While we perceive time as a constant factor in the real world, it can be manipulated in media. Being quite easy for linear media, this is used for various aspects of storytelling e.g., by applying slow motion in movies or TV. Interactive media like VR however poses additional challenges, because user interaction speed is independent from media speed. While it is still possible to change the speed of the environment, for interaction it is also necessary to deal with the emerging speed mismatch, e.g., by slowing down visual feedback of user movements. In this paper, we explore the possibility of such manipulations of visual cues, with the goal of enabling the use of slow motion also in immersive interactive media like VR. We conducted a user study to investigate the impact of limiting angular velocity of a virtual character in first person view in VR. Our findings show that it is possible to use slow motion in VR while maintaining the same levels of presence, enjoyment and susceptibility to motion sickness, while users adjust to the maximum speed quickly. Moreover, our results also show an impact of slowing down user movements on their time estimations.

Home automation faces the challenge of providing ubiquitous, unobtrusive services while empowering users with approachable configuration interfaces. These interfaces need to provide sufficient expressiveness to support complex automation, and notations need to be devised that enable less tech-savvy users to express such scenarios. Rule-based and process-oriented paradigms have emerged as opposing ends of the spectrum; however, their underlying concepts have not been studied comparatively. We report on a contextual inquiry study in which we collected qualitative data from 18 participants in 12 households on the current potential and acceptance of home automation, as well as explored the respective benefits and drawbacks of these two notation paradigms for end users. Results show that rule-based notations are sufficient for simple automation tasks but not flexible enough for more complex use cases. The resulting insights can inform the design of interfaces for smart homes to enable usable real-world home automation for end users.