Thermal perception and regulation are essential for physical exercise. The hue-heat hypothesis suggests that an environment's color temperature, e.g., warm reddish lighting or cold bluish lighting, affects thermal perception and regulation. Virtual reality (VR) enables immersion in any environment. Previous work showed that a VR environment can affect how warm or cold users feel during sedentary VR experiences. However, it is unclear whether such visual thermal cues also influence physiological and perceptual responses during physical exercise. Therefore, we conducted a controlled VR experiment (n = 34) examining whether a virtual heater, either activated or deactivated, influences skin temperature, thermal perception, and perceived exertion while cycling for 20 minutes in each condition. Activation of the virtual heater resulted in significantly higher skin temperature over time and increased thermal sensation compared to the deactivated heater, despite no differences in perceived exertion and heart rate responses. Thereby, we show that visual thermal cues can indeed influence users' thermal perception and thermophysiological responses during physical exercise. Our findings highlight the role of visual environmental cues in shaping thermoregulation during immersive physical exercises.

Although orthotic footwear supports the rehabilitation of lower-limb injuries, it often impairs natural gait control. Due to the lack of additional feedback, patients are unaware of abnormal foot pressure distributions, which can hinder recovery. Prior work has demonstrated the potential of virtual and mixed reality (VR/MR) for gait training with visual feedback. However, it remains unclear how smart insole pressure feedback affects gait and user experience in VR/MR. We conducted a within-subject study with 24 participants, testing four visual feedback modalities across three virtual environments during treadmill walking. Quantitative and qualitative results showed that a virtual forest altered gait, increased engagement, and reduced workload, while a pressure heatmap influenced objective and subjective measures depending on the environment. We provide empirical insights on foot augmentation in immersive settings and contribute design recommendations for future VR/MR gait training applications.

Navigating novel smartphone applications is often complex and unintuitive during the initial onboarding phase. Missing or ineffective guidance can cause misuse, errors, and abandonment, which is particularly critical in domains such as mobile health (mHealth) apps. While previous research has shown potential for onboarding with conversational avatars in mixed reality (MR), the impact of avatars combining gestures and voice for app tutorial guidance remains unknown. To address this gap, we conducted a within-subject study with 24 participants using a smart insole mHealth app as a case example. Participants completed tasks in MR under four conditions varying the presence of avatar voice and animated pointing gestures. Our findings show that tutorial guidance improved with voice and gesture compared to no avatar support, enhancing usability and learning experience while also highlighting remaining challenges. We contribute design implications for avatar-supported guidance in mHealth and broader human-computer interaction (HCI) contexts.

The lack of social acceptability for wearable devices such as orthopedic foot orthoses can lead to irregular usage and missed health benefits, as shown in prior studies. While AI-generated designs have been explored for prototyping aesthetic hand orthoses, their impact on social acceptability, particularly for foot orthoses, remains unknown. The current state of research is limited, as no empirical evidence exists on whether AI-designed orthoses influence acceptance, nor has the role of customized generative pre-trained transformers (GPTs) and specific prompting strategies been examined in this context. To address these gaps, we conducted two mixed-methods studies to investigate (1) the impact of AI-generated orthosis designs on social acceptability compared to existing orthopedic products and development concepts and (2) how a customized GPT and different prompt keywords influence acceptance. Our results show that AI-generated designs significantly enhance social acceptance across orthotic categories. Furthermore, we found that personalized GPTs and targeted prompt keywords significantly influence user perception. Overall, our findings highlight the potential of using AI to create socially acceptable design solutions for wearable technology and offer new applications for future smart devices. We contribute to generative AI in product design and provide concrete recommendations for optimizing prompting strategies to enhance social acceptance.

Virtual reality (VR) allows to embody avatars. Coined the Proteus effect, an avatar’s visual appearance can influence users’ behavior and perception. Recent work suggests that athletic avatars decrease perceptual and physiological responses during VR exercise. However, such effects can fail to occur when users do not experience avatar ownership and identification. While customized avatars increase body ownership and identification, it is unclear whether they improve the Proteus effect. We conducted a study with 24 participants to determine the effects of athletic and non-athletic avatars that were either customized or randomly assigned. We developed a customization editor to allow creating customized avatars. We found that customized avatars reduced perceived exertion. We also found that athletic avatars decreased heart rate while holding weights, however, only when being customized. Results indicate that customized avatars can positively influence users during physical exertion. We discuss the utilization of avatar customization in VR exercise systems.

Perceived temperature and thermoregulation are not only influenced by actual temperature but also by visual perception. For instance, the hue-heat hypothesis posits that warm-colored lighting can increase perceived temperature. Recent work indicates that embodying avatars with visual cues suggesting extreme temperatures influences thermal perception and thermoregulation. However, recent work is limited by short exposure times, inconsistent temperature effects, and the absence of a baseline comparison. Thus, we conducted a study where participants embodied ice, neutral, and fire hands in virtual reality for 15 minutes. We show that thermal sensation is significantly higher with fire hands compared to ice hands, but found no consistent effects on skin temperature. As the effects on thermal sensation remain consistent at least over 15 minutes, we conclude that avatars' appearance can be used to systematically influence users' thermal perception.

Obtaining informed consent is a fundamental ethical requirement in research involving human subjects, designed to ensure autonomy, respect, and the protection of participants. However, new technologies and research methodologies in Human-Computer Interaction (HCI) present unique challenges in maintaining ethical standards and require a deeper understanding of how consent practices are implemented. This scoping review provides a detailed examination of the frameworks, methodologies, and practices for obtaining informed consent in HCI. We present recognized universal principles while also discussing the ethical guidelines, and legal frameworks that underpin consent processes. Furthermore, we analyze the practices of disclosure, screening, consenting, and confirmation to assess how researchers ensure voluntary participation. The review addresses key criticisms and challenges identified in the literature, suggesting improvements and exploring alternative approaches. By offering comprehensive insights into the complexities of informed consent, we underscore the ongoing need for ethical awareness and continuous refinement of ethical conduct in HCI.

Agility ladder training is used by athletes and in rehabilitation to improve coordination and motor skills. Research highlights the potential of visual feedback in virtual reality (VR) to enhance agility ladder training compared to conventional real-world (RW) methods. Moreover, the integration of mixed reality technologies introduces new possibilities for rehabilitation through novel agility ladder concepts. However, the impact of augmented reality (AR) and VR on foot positioning success rates and foot rotation angles compared to RW environment remains underexplored. We conducted an experimental study with 24 participants to assess foot positioning success rates, rotation angles, and perceived workload in AR, RW, and VR environments, using two different visualizations: empty fields and footsteps. The results showed that AR led to significantly lower foot positioning success rates compared to both RW and VR, while VR resulted in greater inward foot rotation angles. Additionally, participants reported a significantly higher perceived workload in AR, which was consistent with qualitative feedback from post-study questionnaires. Our findings reveal the need for improved visual feedback in immersive training environments to enhance performance and reduce cognitive load. We also discuss the challenges of using AR passthrough technology for agility ladder training and provide recommendations for future rehabilitation applications.

Designers of virtual characters use facial expressions to display avatar emotions. Previous work revealed connections between emotions and thermoregulatory, e.g., happiness increases and sadness decreases skin temperature. As virtual reality (VR) enables embodying avatars with any facial expression, it is unclear whether embodying avatars with different emotions also affect users' thermophysiological and emotional responses. We conducted a study with 24 participants who embodied customized avatars displaying happy, neutral, and sad facial expressions in VR. We found that participants' skin temperature was higher with sad avatars than with happy ones while resting. Despite non-significant pairwise comparisons, descriptive statistics suggest an opposite trend for skin temperature responses during grabbing interactions. We also show that participants felt happier while embodying happy avatars compared to sad avatars. Results indicate that avatars' emotions impact users' thermoregulation and affective states. We discuss underlying mechanisms and potential applications.

Agility ladder training is commonly used in fitness and therapy to improve coordination in lower-limb exercises by training precise foot placement. Previous research adapted this training approach to immersive environments and emphasized both the potential and the need for enhanced visual feedback in virtual reality (VR) to improve training outcomes. However, effective visual guidance for such tasks in VR remains underexplored, as it is unclear how spatial user interfaces (UIs) should be designed to support accurate foot placement. To address this gap, we conducted a within-subject study with 40 participants, investigating the effects of two visualization techniques: a Foot-Aligned UI (exocentric, attached to the feet) and a Head-Aligned UI (egocentric, floating in view); combined with color-coded performance feedback. Foot positioning accuracy, rotational control, success rate, and perceived workload were measured during VR-based agility ladder tasks. Results show that the Foot-Aligned UI significantly improved foot placement success rates without increasing cognitive load, compared to the Head-Aligned UI and No UI conditions, which was supported by qualitative feedback. In contrast, color-coded step feedback was perceived as helpful but showed no measurable performance benefit. Based on these findings, we derive design recommendations for spatial UIs to support lower-limb motor training in VR.

Virtual reality enables embodying different avatars. Coined the Proteus effect, previous work found that the visual characteristics of an avatar can cause behavioral, attitudinal, and perceptual effects. Recent work suggests that avatars’ muscularity can even have physiological effects while cycling in virtual reality. As the effects have not been replicated it is, however, unclear how robust they are and if effects are limited to specific activities, such as cycling. Therefore, we conducted a study to understand if avatars’ muscularity also causes physiological and perceptual effects for other tasks and if the effects can be replicated. 16 participants embodied a muscular and a non-muscular avatar while rowing on an indoor rower. We found that over time participants’ heart rates increased significantly slower when embodying a muscular avatar compared to a non-muscular avatar. While not significant, descriptive statistics suggest the same trend for perceived exertion. Overall, the results confirm previous findings and support the conclusion that avatars can cause physiological effects for a range of physical activities.

This paper presents the results of a user study examining the impact of biofeedback awareness on the effectiveness of stress management, utilizing Electrodermal Activity (EDA) as the primary metric within an immersive Virtual Reality (VR). Employing a between-subjects design (N=30), we probed whether informing individuals of their capacity to manipulate the VR environment’s weather impacts their physiological stress responses. Our results indicate lower EDA levels of participants who were informed of their biofeedback control than those participants who were not informed about their biofeedback control. Interestingly, the participants who were informed about the control over the environment also manifested variations in their EDA responses. Participants who were not informed of their ability to control the weather showed decreased EDA measures until the end of the biofeedback phase. This study enhances our comprehension of the significance of awareness in biofeedback in immersive settings and its potential to augment stress management techniques.

In face-to-face social interactions, emotional expressions provide insights into the mental state of an interactive partner. This information can be crucial to infer action intentions and react towards another person’s actions. Here we investigate how facial emotional expressions impact subjective experience and physiological and behavioral responses to social actions during real-time interactions. Thirty-two participants interacted with virtual agents while fully immersed in Virtual Reality. Agents displayed an angry or happy facial expression before they directed an appetitive (fist bump) or aversive (punch) social action towards the participant. Participants responded to these actions, either by reciprocating the fist bump or by defending the punch. For all interactions, subjective experience was measured using ratings. In addition, physiological responses (electrodermal activity, electrocardiogram) and participants’ response times were recorded. Aversive actions were judged to be more arousing and less pleasant relative to appetitive actions. In addition, angry expressions increased heart rate relative to happy expressions. Crucially, interaction effects between facial emotional expression and action were observed. Angry expressions reduced pleasantness stronger for appetitive compared to aversive actions. Furthermore, skin conductance responses to aversive actions were increased for happy compared to angry expressions and reaction times were faster to aversive compared to appetitive actions when agents showed an angry expression. These results indicate that observers used facial emotional expression to generate expectations for particular actions. Consequently, the present study demonstrates that observers integrate information from facial emotional expressions with actions during social interactions.

Balance board training is a promising method to enhance physical rehabilitation for humans with motor problems through interactive exercises. Previous work highlighted the benefts of balance board training in virtual reality (VR) compared to conventional methods. However, it is still unclear how visual target feedback and the presence of an avatar influence balance behavior in immersive environments. We conducted an experimental user study with 24 participants without motor impairments to investigate the effects of visual target feedback and a human avatar on balance performance and perceived workload in VR. Quantitative results show that visual target feedback significantly improves balance performance without increasing workload in VR. In contrast, an avatar shows no effect on performance and workload, which is also confrmed by qualitative feedback. Finally, we discuss the implications of our study for future developments of virtual balance board training exercises and highlight potential applications of visual target feedback.

Increasing research on intelligent wearable technologies, such as smart insoles for mobile health (mHealth) monitoring, brings new challenges for user-centered design, particularly in data visualization. Research shows various developments in mobile apps for monitoring foot health with smart insoles, while emerging trends like chatbot interactions and improved analytic visualizations offer new opportunities to enhance user experience. However, the usability of various health data visualizations remains unvalidated. A mixed-method experimental user study with 30 participants was conducted to assess the usability of three prototype mHealth applications for smart insoles: Analytical, Basic, and Chatbot visualizations. Quantitative results showed that Basic visualization achieved the highest usability, followed by Analytical, and finally Chatbot. Qualitative feedback supported these findings but also highlighted the potential of Chatbot interactions to enhance data understanding in mHealth apps. We discuss implications for future mHealth applications to monitor foot health and propose design recommendations to improve usability in chatbot interactions.

Electromyography (EMG) enables hands-free interactions by detecting muscle activity at different human body locations. Previous studies have demonstrated that input performance based on isometric contractions is muscle-dependent and can benefit from synchronous biofeedback. However, it remains unknown whether stimulation before interaction can help to localize and tense a muscle faster. In a response-based VR experiment (N=21), we investigated whether prior stimulation using visual or tactile cues at four different target muscles (biceps, triceps, upper leg, calf) can help reduce the time to perform isometric muscle contractions. The results show that prior stimulation decreases EMG reaction times with visual, vibrotactile, and electrotactile cues. Our experiment also revealed important findings regarding learning and fatigue at the different body locations. We provide qualitative insights into the participants’ perceptions and discuss potential reasons for the improved interaction. We contribute with implications and use cases for prior stimulated muscle activation.

As our society ages and technology becomes increasingly omnipresent, the use of Mixed Reality (MR) in private and health-related domains inevitably encounters the older population. This intersection presents unique challenges and opportunities for the integration of MR technology into the lives of elderlies. We conducted a qualitative study (N=7) using think-aloud interviews to gain in-depth insights into the usage of MR devices by elderly people. Using thematic analysis we identifed barriers and facilitators for elderly engagement with MR: emotional response, ergonomics and handling, utility, learning competence, and acceptance. Our fndings highlight the roles of timing, responsiveness, and skepticism towards the technology, which can act as a deterrent to the participation of elderlies. We contribute with a refned understanding of the elderly's interaction with MR and recommendations for elderly-centric MR technology adoption.

Humans’ thermal regulation and subjective perception of temperature is highly plastic and depends on the visual appearance of the surrounding environment. Previous work shows that an environment’s color temperature affects the experienced temperature. As virtual reality (VR) enables visual immersion, recent work suggests that a VR scene’s color temperature also affects experienced temperature. It is, however, unclear if an avatar’s appearance also affects users’ thermal perception and if a change in thermal perception even influences the body temperature. Therefore, we conducted a study with 32 participants performing a task in an ice or fire world while having ice or fire hands. We show that being in a fire world or having fire hands increases the perceived temperature. We even show that having fire hands decreases the hand temperature compared to having ice hands. We discuss the implications for the design of VR systems and future research directions.

Planning and organizing user studies can be a challenge for novices and student researchers in human-computer interaction (HCI). We present a web-based study planning toolkit for researchers to support their planning and organization with human subjects. The free and open toolkit contains multiple interactive research applications for (1) the selection of quantitative and qualitative research methods in HCI, (2) automated study design planning for experimental user studies, (3) an automated informed consent generation for studies with human subjects, (4) calendar booking for experimental user studies in shared laboratories, and (5) automated participation confirmation certificates. The toolkit can be helpful for Ph.D. students in supervising novices and undergraduates who need support with their planning and study design choices. The toolkit was actively used over two semesters in multiple HCI lectures and formatively evaluated. We contribute with the whole toolkit and encourage other researchers to contribute and further improve the content.