Simulating wetness in interactive systems is challenging due to the lack of dedicated hygroreceptors in human skin and the complexity of delivering physical moisture. We introduce Moisture Transfer, a perceptual wetness illusion in which users feel moisture at a dry site when cold and wet stimuli are applied nearby. This illusion arises from the brain’s spatial integration of thermal and tactile cues, offering a new pathway to render wetness without direct contact. We investigate this illusion by establishing it with a single finger and show that thermal congruence enhances perceived wetness. We then explored its spatial extent across five fingers, revealing lateral transfer of wetness. Finally, we applied these findings to create a proof-of-concept VR interface that evokes full-hand wetness using minimal actuation. We conclude with design implications for XR and wearable systems and outline future work exploring body-wide wetness illusions and multisensory integration.

Low-latency multimodal feedback is essential for maintaining a high-quality user experience in VR; however, unpredictable network conditions can introduce latency that negatively impacts user experience. This work investigates how users perceive multimodal haptic feedback—specifically thermal (hot/cold) and tactile stimuli—and how latency in such feedback affects user experience. We first measured users’ response times for thermal, tactile, and combined thermal-tactile stimuli. Subsequently, we conducted a psychophysical study to identify delay thresholds for each modality by examining temporal congruency between visual and haptic cues. We designed a haptic delay network simulator to emulate a realistic network environment. Results highlighted that combined thermal-tactile feedback has higher latency tolerance than thermal-only feedback, indicating that multimodal integration can buffer the negative effects of latency. Using these thresholds, we designed controlled latency conditions and assessed user experience. Based on our findings, we propose design recommendations for haptic data transmission in networked VR systems.

This paper reports on a thermal illusion called thermal masking. Thermal masking is a phenomenon induced by thermal referral to completely mask the original thermal sensation, providing thermal sensation only at the tactile site. Three experiments are conducted using thermal and vibrotactile actuators to investigate the nature of thermal masking on human arms. The first experiment investigates the effects of different temperatures on masking. The results show a higher percentage of thermal masking occurs in warm than hot or cold conditions. The second experiment examines how far the thermal masking can be perceived. The results show that masking can reach up to 24 cm from the thermal site. The third experiment explores the interaction space by placing the tactile actuators on the opposite side of the thermal actuator. The results confirm that thermal masking can reach the other side of the arm, and the performance was higher in warm conditions.

This study explores the impact of combining multiple senses on how people perceive wetness in mid-air. We examine how factors like temperature, pressure, and visual stimuli influence the illusion of wetness on users’ palms. The first user study examines these effects and the complex relationships between these variables. The findings suggest that increased temperature and pressure increase the likelihood of perceiving wetness. Interestingly, we note the influence of visual scene content on wetness perception. This leads to our second user study, which investigates how visual context impacts wetness perception. The results demonstrate a strong link between visual content and wetness perception, offering valuable insights for designing immersive virtual reality experiences that enhance sensory perception.

We present a novel approach to render thermal and tactile feedback to the palm and fingertips through thermal and tactile integration. Our approach minimizes the obstruction of the palm and inner side of the fingers and enables virtual object manipulation while providing localized and global thermal feedback. By leveraging thermal actuators positioned strategically on the outer palm and back of the fingers in interplay with tactile actuators, our approach exploits thermal referral and tactile masking phenomena. Through a series of user studies, we validate the perception of localized thermal sensations across the palm and fingers, showcasing the ability to generate diverse thermal patterns. Furthermore, we demonstrate the efficacy of our approach in VR applications, replicating diverse thermal interactions with virtual objects. This work represents significant progress in thermal interactions within VR, offering enhanced sensory immersion at an optimal energy cost.

This study presents a novel method for creating moving thermal sensations by integrating the thermal referral illusion with tactile motion. Conducted through three experiments on human forearms, the first experiment examined the impact of temperature and thermal actuator placement on perceived thermal motion, finding the clearest perception with a centrally positioned actuator under both hot and cold conditions. The second experiment identified the speed thresholds of perceived thermal motion, revealing a wider detectable range in hot conditions (1.8 cm/s to 9.5cm/s) compared to cold conditions (2.4cm/s to 5.0cm/s). Finally, we integrated our approach into virtual reality (VR) to assess its feasibility through two interaction scenarios. Our results shed light on the comprehension of thermal perception and its integration with tactile cues, promising significant advancements in incorporating thermal motion into diverse thermal interfaces for immersive VR experiences.

This paper presents a fabric-based thermal display of a polyester fabric material combined with thermally-conductive materials using an ultrasound haptic display. We first empirically test the thermal generation process in five fabric materials by applying 40 kHz ultrasonic waves to the fabric materials. We also examine their thermal characteristics by applying different frequencies and amplitudes of ultrasonic cues. We show that polyester demonstrates the best thermal performance. We then combine it with thermally-conductive materials, including copper and aluminum, and compare them with the fabric-only condition. Two user studies show that our approach of combining a fabric material with copper and aluminum outperforms fabric-only conditions in thermal perception and thermal level identification. We integrate polyester with aluminum into a glove to explore the use cases in VR and share our findings, insights, limitations, and future works.

This paper investigates the effects of thermal referral and tactile masking illusions to achieve localized thermal feedback on the upper body. Two experiments are conducted. The first experiment uses a 2D array of sixteen vibrotactile actuators $(4\times 4)$ with four thermal actuators to explore the thermal distribution on the user's back. A combination of thermal and tactile sensations is delivered to establish the distributions of thermal referral illusions with different numbers of vibrotactile cues. The result confirms that localized thermal feedback can be achieved through cross-modal thermo-tactile interaction on the user's back of the body. The second experiment is conducted to validate our approach by comparing it with thermal-only conditions with an equal and higher number of thermal actuators in VR. The results show that our thermal referral with a tactile masking approach with a lesser number of thermal actuators achieves higher response time and better location accuracy than thermal-only conditions. Our findings can contribute to thermal-based wearable design to achieve greater user performance and experiences.

We examine mid-air typing data collected from touch typists to evaluate the features and classification models for recognizing finger stroke. A large number of finger movement traces have been collected using finger motion capture systems, labeled into individual finger strokes, and classified into several key features. We test finger kinematic features, including 3D position, velocity, acceleration, and temporal features, including previous fingers and keys. Based on this analysis, we assess the performance of various classifiers, including Naive Bayes, Random Forest, Support Vector Machines, and Deep Neural Networks, in terms of the accuracy for correctly classifying the keystroke. We finally incorporate a linguistic heuristic to explore the effectiveness of the character prediction model and improve the total accuracy.

This paper presents a mid-air thermo-tactile feedback system using an ultrasound haptic display. We design a proof-of-concept thermo-tactile feedback system with an open-top chamber, heat modules, and an ultrasound display. Our approach is to provide heated airflow along the path to the focused pressure point created from the ultrasound display to generate thermal and vibrotactile cues in mid-air simultaneously. We confirm that our system can generate the thermo-tactile stimuli up to 54.2°C with 3.43 mN when the ultrasonic haptic signal was set to 100 Hz with a 12 mm radius of the cue size. We also confirm that our system can provide a stable temperature (mean error=0.25%). We measure the warm detection threshold (WDT) and the heat-pain detection threshold (HPDT). The results show that the mean WDT was 32.8°C (SD=1.12), and the mean HPDT was 44.6°C (SD=1.64), which are consistent with the contact-based thermal thresholds. We also found that the accuracy of haptic pattern identification is similar for non-thermal (98.1%) and thermal conditions (97.2%), showing a non-significant effect of high temperature. We finally confirmed that thermo-tactile feedback further enhances the user experiences.