A Qualitative Investigation of User Transitions and Frictions in Cross-Reality ApplicationsResearch in Augmented Reality (AR) and Virtual Reality (VR) has mostly viewed them in isolation. Yet, when used together in practical settings, AR and VR each offer unique strengths, necessitating multiple transitions to harness their advantages. This paper investigates potential challenges in Cross-Reality (CR) transitions to inform future application design. We implemented a CR system featuring a 3D modeling task that requires users to switch between PC, AR, and VR. Using a talk-aloud study (n=12) and thematic analysis, we revealed that frictions primarily arose when transitions conflicted with users' Spatial Mental Model (SMM). Furthermore, we found five transition archetypes employed to enhance productivity once an SMM was established. Our findings uncover that transitions have to focus on establishing and upholding the SMM of users across realities, by communicating differences between them.2025JWJulius von Willich et al.TU Darmstadt, Telecooperation LabMixed Reality WorkspacesImmersion & Presence ResearchCHI
Assessing the Influence of Visual Cues in Virtual Reality on the Spatial Perception of Physical Thermal StimuliAdvancements in haptics for Virtual Reality (VR) increased the quality of immersive content. Particularly, recent efforts to provide realistic temperature sensations have gained traction, but most often require very specialized or large complex devices to create precise thermal actuations. However, being largely detached from the real world, such a precise correspondence between the physical location of thermal stimuli and the shown visuals in VR might not be necessary for an authentic experience. In this work, we contribute the findings of a controlled experiment with 20 participants, investigating the spatial localization accuracy of thermal stimuli while having matching and non-matching visual cues of a virtual heat source in VR. Although participants were highly confident in their localization decisions, their ability to accurately pinpoint thermal stimuli was notably deficient.2024SGSebastian Günther et al.Technical University of DarmstadtMid-Air Haptics (Ultrasonic)Immersion & Presence ResearchCHI
Tailor Twist: Assessing Rotational Mid-Air Interactions for Augmented RealityMid-air gestures, widely used in today's Augmented Reality (AR) applications, are prone to the “gorilla arm” effect, leading to discomfort with prolonged interactions. While prior work has proposed metrics to quantify this effect and means to improve comfort and ergonomics, these works usually only consider simplistic, one-dimensional AR interactions, like reaching for a point or pushing a button. However, interacting with AR environments also involves far more complex tasks, such as rotational knobs, potentially impacting ergonomics. This paper advances the understanding of the ergonomics of rotational mid-air interactions in AR. For this, we contribute the results of a controlled experiment exposing the participants to a rotational task in the interaction space defined by their arms' reach. Based on the results, we discuss how novel future mid-air gesture modalities benefit from our findings concerning ergonomic-aware rotational interaction.2023DSDominik Schön et al.Technical University of DarmstadtFull-Body Interaction & Embodied InputAR Navigation & Context AwarenessCHI
TicTacToes: Assessing Toe Movements as an Input ModalityFrom carrying grocery bags to holding onto handles on the bus, there are a variety of situations where one or both hands are busy, hindering the vision of ubiquitous interaction with technology. Voice commands, as a popular hands-free alternative, struggle with ambient noise and privacy issues. As an alternative approach, research explored movements of various body parts (e.g., head, arms) as input modalities, with foot-based techniques proving particularly suitable for hands-free interaction. Whereas previous research only considered the movement of the foot as a whole, in this work, we argue that our toes offer further degrees of freedom that can be leveraged for interaction. To explore the viability of toe-based interaction, we contribute the results of a controlled experiment with 18 participants assessing the impact of five factors on the accuracy, efficiency and user experience of such interfaces. Based on the findings, we provide design recommendations for future toe-based interfaces.2023FMFlorian Müller et al.LMU MunichFoot & Wrist InteractionCHI
Smooth as Steel Wool: Effects of Visual Stimuli on the Haptic Perception of Roughness in Virtual RealityHaptic Feedback is essential for lifelike Virtual Reality (VR) experiences. To provide a wide range of matching sensations of being touched or stroked, current approaches typically need large numbers of different physical textures. However, even advanced devices can only accommodate a limited number of textures to remain wearable. Therefore, a better understanding is necessary of how expectations elicited by different visualizations affect haptic perception, to achieve a balance between physical constraints and great variety of matching physical textures. In this work, we conducted an experiment (N=31) assessing how the perception of roughness is affected within VR. We designed a prototype for arm stroking and compared the effects of different visualizations on the perception of physical textures with distinct roughnesses. Additionally, we used the visualizations' real-world materials, no-haptics and vibrotactile feedback as baselines. As one result, we found that two levels of roughness can be sufficient to convey a realistic illusion.2022SGSebastian Günther et al.Technical University of DarmstadtVibrotactile Feedback & Skin StimulationImmersion & Presence ResearchCHI
BikeAR: Understanding Cyclists' Crossing Decision-Making at Uncontrolled Intersections using Augmented RealityCycling has become increasingly popular as a means of transportation. However, cyclists remain a highly vulnerable group of road users. According to accident reports, one of the most dangerous situations for cyclists are uncontrolled intersections, where cars approach from both directions. To address this issue and assist cyclists in crossing decision-making at uncontrolled intersections, we designed two visualizations that: (1) highlight occluded cars through an X-ray vision and (2) depict the remaining time the intersection is safe to cross via a Countdown. To investigate the efficiency of these visualizations, we proposed an Augmented Reality simulation as a novel evaluation method, in which the above visualizations are represented as AR, and conducted a controlled experiment with 24 participants indoors. We found that the X-ray ensures a fast selection of shorter gaps between cars, while the Countdown facilitates a feeling of safety and provides a better intersection overview.2022AMAndrii Matviienko et al.Technical University of DarmstadtExternal HMI (eHMI) — Communication with Pedestrians & CyclistsAR Navigation & Context AwarenessCHI
Squeezy-Feely: Investigating Lateral Thumb-Index Pinching as an Input ModalityFrom zooming on smartphones and mid-air gestures to deformable user interfaces, thumb-index pinching grips are used in many interaction techniques. However, there is still a lack of systematic understanding of how the accuracy and efficiency of such grips are affected by various factors such as counterforce, grip span, and grip direction. Therefore, in this paper, we contribute an evaluation (N = 18) of thumb-index pinching performance in a visual targeting task using scales up to 75 items. As part of our findings, we conclude that the pinching interaction between the thumb and index finger is a promising modality also for one-dimensional input on higher scales. Furthermore, we discuss and outline implications for future user interfaces that benefit from pinching as an additional and complementary interaction modality.2022MSMartin Schmitz et al.Technical University of DarmstadtIn-Vehicle Haptic, Audio & Multimodal FeedbackHand Gesture RecognitionCHI
CameraReady: Assessing the Influence of Display Types and Visualizations on Posture GuidanceComputer-supported posture guidance is used in sports, dance training, expression of art with movements, and learning gestures for interaction. At present, the influence of display types and visualizations have not been investigated in the literature. These factors are important as they directly impact perception and cognitive load, and hence influence the performance of participants. In this paper, we conducted a controlled experiment with 20 participants to compare the use of five display types with different screen sizes: smartphones, tablets, desktop monitors, TVs, and large displays. On each device, we compared three common visualizations for posture guidance: skeletons, silhouettes, and 3d body models. To conduct our assessment, we developed a mobile and cross-platform system that only requires a single camera. Our results show that compared to a smartphone display, larger displays show a lower error (12%). Regarding the choice of visualization, participants rated 3D body models as significantly more usable in comparison to a skeleton visualization.2021HEHesham Elsayed et al.Human Pose & Activity RecognitionDance & Body Movement ComputingDIS
Therminator: Understanding the Interdependency of Visual and On-Body Thermal Feedback in Virtual RealityRecent advances have made Virtual Reality (VR) more realistic than ever before. This improved realism is attributed to today's ability to increasingly appeal to human sensations, such as visual, auditory or tactile. While research also examines temperature sensation as an important aspect, the interdependency of visual and thermal perception in VR is still underexplored. In this paper, we propose Therminator, a thermal display concept that provides warm and cold on-body feedback in VR through heat conduction of flowing liquids with different temperatures. Further, we systematically evaluate the interdependency of different visual and thermal stimuli on the temperature perception of arm and abdomen with 25 participants. As part of the results, we found varying temperature perception depending on the stimuli, as well as increasing involvement of users during conditions with matching stimuli.2020SGSebastian Günther et al.Technische Universität DarmstadtMid-Air Haptics (Ultrasonic)Immersion & Presence ResearchCHI
Walk The Line: Leveraging Lateral Shifts of the Walking Path as an Input Modality for Head-Mounted DisplaysRecent technological advances have made head-mounted displays (HMDs) smaller and untethered, fostering the vision of ubiquitous interaction in a digitally augmented physical world. Consequently, a major part of the interaction with such devices will happen on the go, calling for interaction techniques that allow users to interact while walking. In this paper, we explore lateral shifts of the walking path as a hands-free input modality. The available input options are visualized as lanes on the ground parallel to the user's walking path. Users can select options by shifting the walking path sideways to the respective lane. We contribute the results of a controlled experiment with 18 participants, confirming the viability of our approach for fast, accurate, and joyful interactions. Further, based on the findings of the controlled experiment, we present three example applications.2020FMFlorian Müller et al.Technische Universität DarmstadtFull-Body Interaction & Embodied InputEye Tracking & Gaze InteractionCHI
Assessing the Accuracy of Point & Teleport Locomotion with Orientation Indication for Virtual Reality using Curved TrajectoriesRoom-scale Virtual Reality (VR) systems have arrived in users' homes where tracked environments are set up in limited physical spaces. As most Virtual Environments (VEs) are larger than the tracked physical space, locomotion techniques are used to navigate in VEs. Currently, in recent VR games, point & teleport is the most popular locomotion technique. However, it only allows users to select the position of the teleportation and not the orientation that the user is facing after the teleport. This results in users having to manually correct their orientation after teleporting and possibly getting entangled by the cable of the headset. In this paper, we introduce and evaluate three different point & teleport techniques that enable users to specify the target orientation while teleporting. The results show that, although the three teleportation techniques with orientation indication increase the average teleportation time, they lead to a decreased need for correcting the orientation after teleportation.2019MFMarkus Funk et al.Technische Universität DarmstadtHead-Up Display (HUD) & Advanced Driver Assistance Systems (ADAS)Eye Tracking & Gaze InteractionImmersion & Presence ResearchCHI
Mind the Tap: Assessing Foot-Taps for Interacting with Head-Mounted DisplaysFrom voice commands and air taps to touch gestures on frames: Various techniques for interacting with head-mounted displays (HMDs) have been proposed. While these techniques have both benefits and drawbacks dependent on the current situation of the user, research on interacting with HMDs has not concluded yet. In this paper, we add to the body of research on interacting with HMDs by exploring foot-tapping as an input modality. Through two controlled experiments with a total of 36 participants, we first explore direct interaction with interfaces that are displayed on the floor and require the user to look down to interact. Secondly, we investigate indirect interaction with interfaces that, although operated by the user's feet, are always visible as they are floating in front of the user. Based on the results of the two experiments, we provide design recommendations for direct and indirect foot-based user interfaces.2019FMFlorian Müller et al.Technische Universität DarmstadtFoot & Wrist InteractionCHI
Off-Line Sensing: Memorizing Interactions in Passive 3D-Printed ObjectsEmbedding sensors into objects allow them to recognize various interactions. However, sensing usually requires active electronics that are often costly, need time to be assembled, and constantly draw power. Thus, we propose off-line sensing: passive 3D-printed sensors that detect one-time interactions, such as accelerating or flipping, but neither require active electronics nor power at the time of the interaction. They memorize a pre-defined interaction via an embedded structure filled with a conductive medium (e.g., a liquid). Whether a sensor was exposed to the interaction can be read-out via a capacitive touchscreen. Sensors are printed in a single pass on a consumer-level 3D printer. Through a series of experiments, we show the feasibility of off-line sensing.2018MSMartin Schmitz et al.Technische Universität DarmstadtDesktop 3D Printing & Personal FabricationCircuit Making & Hardware PrototypingCHI