Feeling ownership of a virtual body in Virtual Reality (VR) enhances the immersion and quality of user experience. Inducing body ownership in VR is mainly based on the Rubber Hand Illusion (RHI) experiment, where watching a rubber hand being stroked while the natural hidden hand is synchronously stroked, induces an illusion of ownership for the rubber hand. Tactile feedback plays a vital role in inducing the RHI in VR. While previous research showed that vibrotactile feedback significantly improves the quality of the illusion, it remains unclear what type of brushing is more effective. In this study, we consider two brushing parameters: (1) self-brushing versus brushing by others and (2) discrete versus continuous brushing. We developed a VR simulation and a haptic sleeve to simulate the RHI through five experimental conditions: control (without haptics), self-discrete, self-continuous, other-discrete, and other-continuous. A total of 85 participants, divided across the 5 experimental conditions, took part in the experiment. The quality of the RHI was assessed using two standard tests, namely proprioceptive drift and an ownership illusion questionnaire. The results indicated that while the control condition (no brushing) showed no significant improvement, all types of brushing resulted in a significant increase in the quality of the illusion. Furthermore, across the four brushing conditions, the self-continuous condition showed a significant increase in the quality of the illusion as compared to the control condition.
A body-penetrating phantom sensation refers to a tactile experience in which the perceived location shifts between the dorsal and ventral sides of the body over time, resulting in the illusion of a tactile stimulus passing through the body. This study explores the integration of auditory and tactile stimuli to enhance the perception of body-penetrating phantom sensations. Combining vibrotactile feedback with various sounds commonly used in gaming, we investigate how multisensory configurations improve their realism, directional clarity, and user satisfaction. The experimental results demonstrate that penetration-related sounds significantly enhance perceived realism and satisfaction. We also compare the changes in emotional pleasantness and arousal levels resulting from integration of sound and tactile stimuli, along with a summary of the subjective responses. Our findings highlight the critical role of semantic harmony between auditory and tactile information, offering actionable insights for improving the realism and immersion of physical interactions in virtual environments.
Individuals who lack tactile and/or proprioceptive sensations in their lower limbs commonly report postural and locomotive imbalance. To mitigate imbalance, haptic feedback has been implemented using devices that employ external sensors and waist-worn actuators for sensory augmentation. Analyses of the effectiveness of these devices have primarily focused on balance outcomes and generally disregard the potential effect of the user's varying activities or anthropometric data on their perception of the haptic feedback. Since motor activity can influence haptic perception, we investigate vibrotactile cue localizability in a waist-worn haptic device for two conditions, standing and walking on a treadmill at a self-selected speed. In this preliminary study, ten participants without sensorimotor deficits wore a waistband equipped with seven vibrotactile actuators. Vibrotactile cues were played at randomized locations during standing and walking, and participants reported the perceived stimulation location. In addition, we recorded relevant anthropometric data for each participant. In both standing and walking conditions, participants correctly localized 51% of the vibrotactile cues on average. When considering zonal accuracy, or localization within one vibrotactor position, participants, on average, achieved an accuracy of 91 % in standing and 90% in walking.
Haptic cues are crucial in the elicitation of emotions, as affective touch research has revealed. However, our increasingly digital lives have eroded access to these cues, having detrimental effects. Thus, the investigation of alternative ways to elicit equivalent emotional responses to those of affective touch merits attention. In the present study, two online experiments examining the emotional responses to sounds of organic affective touch were conducted. In Experiment 1, the emotional responses to a series of organic affective touch sounds, compared to object-based sounds, were evaluated. In Experiment 2, the influence of manipulating the stated nature of the sounds, as either affective touch or object-based, on the emotional responses to the sounds was investigated. The results revealed different patterns in the emotional responses to the affective touch sounds compared to the object-based ones, although participants could not confidently identify affective touch. Furthermore, explicitly stating that the sounds involved object-based interactions increased the evoked valence of two specific object-based sounds. These findings highlight the importance of meaning in affective touch and reveal the high complexity of the sonification of touch. This study paves the way for future research on the emotions of auditory affective touch.
Exploring perceptual dissimilarity spaces of largescale Tactons (i.e., Tactile icons) can inform the design of distinguishable haptic feedback. Yet, collecting pairwise similarity ratings for entire Tacton sets becomes costly as set size increases, prompting the need for alternative methods like subset aggregation. Despite previous efforts, little systematic investigation exists on efficient subset size or participant number needed to estimate large-scale Tacton perceptual spaces within a bounded error threshold. We address this gap by introducing a model that simulates between-subject variability in similarity perception. The model explores various distributions under different conditions, including total Tacton numbers and subset-to-total ratios, to guide user studies. Guided by these simulations, we evaluated subset aggregation with three small-scale Tacton sets (12 or 14 patterns) and one large-scale set (48 patterns). Study 1 revealed that initial simulations underestimated real-world variability. We refined the model, ran simulations for larger-scale conditions, and validated them in subsequent studies. The updated model closely matched reality, showing that designers can use our subset aggregation method to prototype perceptual spaces for large-scale Tacton sets. Notably, 4-7 observations were sufficient to achieve. = 0.6, compared to the typical 12 required for generalization. We discuss the efficacy of subset aggregation and future research directions.
Smoothness is an essential tactile characteristic for virtual texture simulation. However, research on its haptic ren-dering remains limited compared to the well-explored domain of roughness. Existing methods often define smoothness as simply the absence of roughness, oversimplifying its continuous nature and limiting the potential of haptic systems to fully express its quality. In this study, we introduce a novel haptic parameter, continuity length (CL), designed to render smoothness through continuous feedback. CL represents the continuous shift of the feedback point over a specified length, enabling spatial continuity and creating a seamless tactile experience. Furthermore, when feedback is applied in a fixed direction, regardless of the user's hand movements, misalignment between the hand movement and the feedback can diminish the perception of smoothness in active touch scenarios involving exploratory interaction with objects. To address this, we propose a CL-based movement-adaptive haptic rendering approach. By dynamically adjusting the feedback point in the opposite direction of the user's hand movement, this method ensures alignment between movement and feedback, preserving tactile continuity. User studies show that the CL-based adaptive rendering effectively conveys smoothness, especially for textures like cloth and fur. This approach enhances the expressive capabilities of haptic systems, enabling richer tactile experiences in virtual reality.
Previous works have shown that vibrations under the feet can significantly enhance the walking experience in Virtual Reality (VR). However, such approaches often require specialized hardware. Therefore, in this paper, we study if vibrations in the hands could represent a simple and cost-effective alternative to improve the walking experience in VR. We conducted a user study comparing vibrations displayed in the hands, vibrations under the feet, and no vibration in a VR passive walking simulation during which participants were seated and embodied a first-person avatar. We compared the different conditions regarding: the sensation of walking, avatar embodiment, cybersickness, and comfort. Interestingly, our results show that vibrations in the hands significantly increase the sensation of walking and embodiment compared to no vibration. Moreover, no significant difference is observed between vibrations under the feet and in the hands concerning the sensation of walking. Still, embodiment is higher with vibrations under the feet. No significant differences in cybersickness or comfort were observed between vibrations displays. Overall, our results promote using vibrations in the hands as a cost-effective and suitable alternative to vibrations under the feet in VR applications for which the walking sensation is prominent, leveraging for instance vibrations embedded in VR controllers.
Medical palpation is a vital diagnostic technique where practitioners assess a patient's condition through tactile examination. Advancements in remote health technologies should emphasize supporting tactile/haptic modalities to enable some aspects of physical examination to be conducted at a distance. In thyroid examinations, differentiating nodule sizes is critical for identifying malignant lumps. This study investigates how palpation motion affects the sensing performance of single-point normal force sensors in detecting thyroid nodules. Using a phantom skin model with lumps of varied sizes and depths, force data was captured and visualized as a stiffness distribution (tactile imaging). The captured lump shapes were compared to actual shapes using Correlation Coefficient (CC), Mean Squared Error (MSE), and Structural Similarity Index (SSIM) methods. Results showed that single-point normal force sensors effectively detect lumps, particularly during typical palpation motions such as Poke and Push & Pull, with Poke consistently yielding superior performance across various sizes and depths. However, estimating lump shapes becomes increasingly challenging as lump depth increases, regardless of the motion applied. These findings emphasize the importance of motion in optimizing single-point sensors for palpation and provide valuable insights for developing sensorized gloves for clinical use, particularly in remote healthcare systems.
We experience a sense of adhesion when touching a lotion or adhesive tape with a finger and attempting to pull it off. This sense of adhesion is considered an important element of tactile sensation. However, previous methods for presenting this sensation have been limited, and most require relatively large devices. This study proposes a compact method for presenting a sense of adhesion using an electro-tactile display. The electrotactile display can be made wearable, and it allows flexible control over stimulation timing and area. We propose a method for evoking a sense of adhesion by delivering cutaneous electrical stimulation at the timing when a pulling force is generated between the finger and the adhesive object. Additionally, we investigated a method for reproducing changes in the contact area. Experimental results showed that electrical stimulation successfully induced a sense of adhesion when the finger was lifted from the adhesive surface. The results also suggest that stimulation timing contributes more to the perception of adhesion than changes in the stimulation area.
Pressing motions have traditionally been regarded as the most effective method for discerning object compliance. However, recent studies suggest that humans adopt sliding motions just as frequently as pressing motions for this purpose. Sliding exploration inevitably induces friction, which is in part determined by material softness. This study demonstrates that friction provides crucial cues for judging softness. To investigate the role of sliding friction in compliance judgment, this study compares three tactile exploration methods. sliding, rolling, and pressing.using a shaft ball bearing. Participants assessed the softness of seven rubber materials through the bearing under controlled conditions. In the sliding mode, the outer ring of the bearing slid over the materials, generating significant friction. In the rolling mode, the inner ring was held stationary while the outer ring rolled over the material surfaces, minimizing friction. In the pressing mode, participants applied only vertical force using the bearing, with sliding and rolling motions prohibited. Consistent force application was ensured using a balance scale, and participants ranked the materials by perceived compliance for each method. Results indicate that sliding provides the most reliable cues for judging physical compliance, followed by pressing, while rolling produces lower accuracy. These findings highlight the instrumental role of friction in accurately perceiving compliance during tactile exploration.
Haptics is one of the critical sensory input modalities through which humans acquire information from both the external environment and their own bodies. Transcutaneous electrical stimulation has been adopted as a sensory presentation technique among the various haptic feedback methods. Due to its high responsiveness and compact and lightweight design advantages, transcutaneous electrical stimulation stands out from other haptic approaches and has been applied in various wearable devices and interfaces. This review examines four types of transcutaneous electrical stimulation methods for haptics, namely electrotactile stimulation, electrical stimulation of nerve bundles, electrical stimulation of muscles, and electrical stimulation of tendons, from the perspectives of applications and device development. By providing a comprehensive overview of these methods, we also identify key challenges in the field and propose directions for future research. Specifically, we discuss five themes: combined electrical stimulation, the need for qualitative evaluation, the risk of confusion from identical terminology in different stimulation methods, the importance of interface research geared toward practical implementation, and individual differences in the perception of induced sensation.
This paper proposes a method for controlling the stiffness of a thermally driven actuator by leveraging the phase transition of a low-boiling-point liquid. Using a Peltier device for cooling, the reduction in actuator stiffness can be precisely adjusted. Experiments demonstrated the actuator's effectiveness, particularly in handling fragile objects with precision, ensuring delicate interactions with contact surfaces. Since stiffness is adjusted within a safe temperature range, this approach shows promise for applications involving direct human contact, such as the outer surfaces of social robots (robot skin).
This study proposes a method to represent a 360degree cold sensation by optimizing the use of jet nozzles, considering the curved geometry of the human body. The method leverages the Coand.a effect, a phenomenon where jets adhere to curved surfaces, to achieve wide-area cold perception with a reduced number of jet nozzles. To determine the nozzle conditions required to exceed the threshold of 360-degree cold perception throughout the neck, the target body part of this study, temperature changes were measured using a silicone phantom. Experimental results indicate that a single nozzle was insufficient to exceed the threshold, whereas two nozzles with an internozzle angle of 90 degree or greater successfully exceeded the required temperature change for cold perception. A user study was conducted to evaluate participants 'perceived cold sensation across the neck. The results confirmed that the proposed method can provide 360-degree cold sensation. They also demonstrated statistically significant differences in the effective angle ranges for 360-degree cold sensation between different nozzle-tip directions; parallel (83.0 to 118.4 degree) and center (124.7 to 139.4 degree) nozzle-tip configurations. These findings offer valuable insights that could contribute to the advancement of future thermal displays.
Mid-air haptic systems use focused ultrasound to create tactile sensations in free space. However, predicting and calibrating these systems according to human perception often requires complex multi-physics models or lengthy user studies. In this work, we address this challenge by conducting an extensive measurement campaign, capturing perceived intensity, acoustic pressure, and force across varying heights and device voltages. Using this data, we evaluate four linear models to predict perceived intensity, culminating in a model that combines normalized force and distance. This model achieves strong predictive accuracy, demonstrating that force is a practical and effective predictor of perceived intensity. Our findings show that force, measured using an affordable precision scale, offers a straightforward alternative to complex pressure-based approaches, providing an accessible framework for characterizing mid-air haptic systems. This approach enables efficient, perception-driven design and optimization of mid-air haptic applications.
We present CrazyJoystick, a flyable handheld joy-stick allowing seamless interaction methods to change between joystick and hand-tracking while displaying on-demand haptic feedback in extended reality (XR). Our system comprises a quadrotor that can autonomously approach the user when needed, addressing the limitations of conventional handheld and wearable devices that require continuous carrying throughout interactions. CrazyJoystick dynamically reallocates all thrust for haptic rendering during stationary states, eliminating the need to hover while delivering feedback. A customized cage allows users to grasp the device and interact with virtual objects, receiving 3.5 degree-of-freedom feedback. This novel transition method allows us to harvest the aerial mobility from multi-rotor based haptic devices, while having high force-to-weight ratios from being handheld during interaction. This paper describes the design and implementation of CrazyJoystick, evaluates its force and torque performance, and usability of the system in three VR applications. Our evaluation of torque rendering found that users can perceive the direction with an accuracy of 92.2%. User studies further indicated that the system significantly improves presence in VR environments. Participants found on-demand haptic feedback intuitive and enjoyable, emphasizing the potential of CrazyJoystick to redefine immersive interactions in XR through portable and adaptive feedback mechanisms.
Surgeons require accurate catheter visualization and force estimation during catheter-based surgeries. Segmentation is crucial for both catheter visualization and force estimation purposes. However, using separate models for segmentation and force estimation is computationally costly. Recently, sensor-free vision/deep learning-based models have shown reasonable performance in estimating the applied forces during such surgeries, aiming to reduce the risk of surgical error. These models, however, require pre-processing to cleanly segment the catheter from the background in input images, which increases computational complexity and reduces system throughput. In this work, an encoder-decoder architecture is presented to simultaneously segment the catheter and estimate the applied forces in 2D. The presented method is designed to be deployed on a monoplane fluoroscopy machine. This multi-output network takes a raw image of the catheter's deflection and outputs both the segmented shape of the catheter and the estimated forces in 2D. Similar to object detection models, the network solves a classification problem for segmentation and a regression problem for force estimation. This integrated approach provides the estimated forces and segmented catheter shape within a single end-to-end model. Validation results show that the model accurately maps raw RGB images to the 2D force space and precisely segments the catheter.
This paper introduces a hybrid passivity-digital twin (P-DT) control strategy for teleoperation to enhance haptic feedback in partially unknown remote environments. While Digital Twin-based teleoperation mitigates communication delays through model-based interaction, it may provide less accurate force feedback when the model is insufficiently developed. To address this, the proposed hybrid P-DT strategy dynamically switches between passivity-based and Digital Twin-based control modes, depending on the quality of task perception (QoTP), which reflects the quality of the Digital Twin model. Passivity-based control is used to ensure stable but distorted feedback during the modeling phase. DT-based control provides accurate and responsive feedback once the QoTP metric indicates sufficient model quality. Experimental results under various delays and model update conditions show that the hybrid P-DT strategy outperforms standalone passivity-based and DT-based methods, with subjective quality ratings improving by up to 80% under a 150 ms delay.
Wearable haptic devices can provide haptic feedback in both active and passive touch interactions. In virtual or extended reality environments, wearable devices also enable referred haptic feedback, where touch sensation expected in one place on the body is directed to another. How people perceive the distinction between these feedback forms has been relatively under-explored, especially considering the additional role that vision plays in our multisensory understanding of the world. To explore how active and passive touch affect the perception of referred haptic feedback, we conducted an experiment in VR where participants chose the stiffer of two springs in a 2-interval, 2-alternative forced-choice design. We find that participants can be categorized into two groups based on the different strategies they employ for making the decision - those with a haptic or a visual prior, similar to related work. We also considered both active and passive feedback conditions. Notably, people are more accurate in judging haptic stiffness during the active case. Our results have implications for designers of virtual systems and simulations where users receive various sensory inputs, both via active and passive interactions, with potential mismatches due to latency, bandwidth, or design issues.
Self-Haptics is a tactile feedback technique where users utilize their own body to generate tactile sensations. This method allows the body to act purely as a prop, making it useful for virtual objects and user interfaces not directly related to the body. However, a method for maintaining the sense of ownership (SoO) and agency (SoA) of the user's body and interaction targets that aligns with the perceptual interaction by visual cues does not established. To address this, we present the concept of “(Not My) Self-Haptics,” which aims to resolve these inconsistencies, leveraging vision's dominance in sensory integration. Our study proved how the task performance and the user's experience, including SoO and SoA toward a virtual keypad (VPad) displayed at the position of the real hand (RHand), changes based on the visual appearance of the VHand during the interaction with the VPad. The results show that displaying the VHand in a position different from the RHand or hiding the VHand significantly reduces SoO and SoA toward the VPad, with this effect more pronounced when the RHand faces downward. These findings contribute to the understanding of the interaction between visual and tactile sensations in Self-Haptics and the realization of “(Not My) Self-Haptics”.
Virtual reality (VR) experiences are increasingly employed as tools for pain management. Conventional VR-based pain reduction strategies rely on distraction of the user's attention from the source of the stimulus. However, these strategies are less effective for individuals with difficulty shifting their attention, highlighting the need for alternative methods. This study introduces a novel approach to pain reduction by modifying the appearance of the stimulus source, altering the context as less unpleasant (contextual modification). This method let users to misinterpret the source of the stimulus. The experiment used an animation of a cat scratching a user as a new context, and investigated whether the discomfort threshold, stimulus interpretation, discomfort level, and intensity of discomfort generated by electrical stimulation could be affected. We conducted this evaluation in both VR and augmented reality (AR) environments. Results indicated that the simultaneous presentation of cat animation synchronized with stimulus increased the discomfort threshold and reduced discomfort and pain compared to the presentation of electrical stimuli alone. The effectiveness of this intervention diminished when a temporal delay was set between the stimulus and the animation.
