Motion, conveyed through motion platform movements on which the audience is seated, is the most commonly employed four-dimensional (4D) effect. It enhances immersion and influences emotional responses, with its impact varying depending on design factors. This variation suggests the potential for optimizing audience emotions through motion design. However, previous studies have either overlooked motion design factors or focused on single motion types, limiting the generalizability of their findings. This study focused on 4D ride films, which provide first-person ride experience. We examined the effects of motion presence and developed regression models to explain the relationship between motion design factors and emotional intensity. Models were constructed for representative emotions such as confused and urgent, using maximum amplitudes as independent variables. Based on these models, we proposed motion design guidelines to optimize emotional intensity by adjusting the maximum amplitudes of pitch, roll, and heave. These findings will help 4D ride film producers elicit the intended emotional intensity in audiences.

Multimodal haptic feedback that combines electrical muscle stimulation (EMS) and vibrotactile signals can create richer, more immersive experiences than those using a single modality. EMS delivers kinesthetic feedback by inducing muscle contractions, simulating force sensations that complement tactile stimuli from mechanical vibrations. However, presenting these stimuli concurrently can lead to perceptual interference, where one modality masks or alters the perception of the other. Temporal alignment between stimuli is also critical, as asynchrony can affect the perceived quality of haptic sensations. To investigate these phenomena, we conducted three user studies with a total of 40 participants (12, 12, and 16, respectively), focusing on mutual masking effects and temporal order perception between EMS and vibration. Our findings suggest that vibration can alleviate the tingling and discomfort commonly associated with EMS, effectively mitigating these unwanted sensations. Conversely, the presence of EMS increases the Just Noticeable Difference (JND) in vibration frequency discrimination, indicating a decrease in sensitivity to vibratory changes. Additionally, participants generally perceived the stimuli as simultaneous when EMS preceded vibration by 100 to 200 milliseconds. We discuss these findings and present four design guidelines for multimodal haptic rendering with EMS and vibrations in user applications.

This paper proposes the use of reaction wheels in parallel mechanisms for physical human-robot interaction during the co-manipulation of large payloads. The concept combines the advantages of a mechanically backdrivable robot - for hands-on-payload interaction - with the reactiveness of flywheels for the compensation of inertial loads, thereby leading to a smooth and low-inertia rendering. In the proposed approach, gravity compensation and dynamic compensation are partitioned and assigned to two subsets of actuators, namely the backdrivable joint actuators and the flywheel actuators, the latter being smaller and properly geared actuators to benefit from faster dynamics for interaction stability purposes. Simulation results of a human interaction with a planar robot to displace a payload show that the desired dynamic behaviour of the moving platform is correctly rendered, while indicating that the inertia compensation torques may vary more quickly than the gravity torques, which supports the proposed idea. Experiments are also conducted to validate the rendering of the desired virtual dynamics to the user.

Drilling is an essential procedure in many orthopedic surgeries. Especially in femoral neck fracture surgery, any loss of control can lead to secondary injury to the patient. Consequently, it is imperative for orthopaedists to undergo extensive training to master the appropriate haptic interaction. In this work, a virtual drilling surgery training system with high-fidelity haptic feedback is developed for femoral neck fracture. First, to achieve realistic visual rendering, the external boundary of femur is reconstructed using Triple dexel, allowing for fast and realistic surface reconstruction. Next, the heterogeneous and hierarchical structure of femur is reconstructed using multi-morphology with three periodic minimal surface (TPMS) design approaches. Then, a haptic interaction algorithm based on Triple dexel and TPMS is proposed. This algorithm uses the TPMS equations to quickly compute the densities of the bone chips produced by Triple dexel Boolean operations, thus simulating the variation in porosity at different positions of the bone and providing precise haptic feedback during the drilling process. Finally, a robotic experimental platform is established, and the proposed force model is verified using bovine bones. The results show that the measured values are consistent with the experimental values. Furthermore, evaluation of the training system with medical students as participants shows that a fine haptic rendering improves users' hand-eye coordination skills.

Electrotactile displays are a promising technology that combines the simplicity of implementation using only electronic circuits with the flexibility to deliver tactile sensations across many body sites. In recent years, their applications and research have rapidly advanced. This article provides an overview of studies published in IEEE Transactions on Haptics, covering diverse aspects such as application domains of electrotactile stimulation, techniques for stabilizing percepts, methods for efficient information rendering, and the use of electrotactile displays as tools for investigating human tactile perception. Through this review, the engineering and scientific potential of electrotactile interfaces is highlighted, along with prospects for realizing future tactile displays that are low-cost, high-density, and large-area.

Understanding haptic interactions between fingers and piano keys is essential for uncovering the sensorimotor mechanisms underlying piano performance. In the present study, we developed a sensor-integrated piano keyboard capable of monitoring three-dimensional (3D) forces applied to the keys, achieved by embedding MEMS sensor devices in both white and black keys spanning an entire octave (C4 to C5). The system captures both vertical (depressing) and horizontal (frictional) forces, offering novel insights into how pianists utilize friction to execute complex finger movements in playing note sequences and chords. We describe the system's design and functionality, and present representative results demonstrating its capabilities. Our findings reveal that the temporal profiles of both vertical and horizontal forces contain rich information about physical mechanisms underlying pianistic skills. Moreover, we report novel observations of the dynamic force interaction between the fingers and key surfaces. This system offers a valuable tool for analyzing the sensorimotor foundations of pianistic skills and for providing objective data to support piano pedagogy.

We developed a new aerial push-button with tactile feedback using focused airborne ultrasound. This study has two significant novelties compared to past related studies: 1) ultrasound emitters are equipped behind the user's finger and reflected ultrasound emission that is focused just above the solid plane placed under the finger presents tactile feedback to a finger pad, and 2) tactile feedback is presented at two stages during pressing motion; at the time of pushing the button and withdrawing the finger from it. The former has a significant advantage in apparatus implementation in that the input surface of the device can be composed of a generic thin plane including touch panels, potentially capable of presenting input touch feedback only when the user touches objects on the screen. We experimentally found that the two-stage tactile presentation is much more effective in strengthening perceived tactile stimulation and believability of input completion when compared with a conventional single-stage method. This study proposes a composition of an aerial push-button in much more practical use than ever. The proposed system composition is expected to be one of the simplest frameworks in the airborne ultrasound tactile interface.

In this paper, we present a virtual training platform for soldering based on immersive visual feedback (i.e., a Virtual Reality (VR) headset) and scaffolded guidance (i.e., disappearing throughout the training) provided through a haptic device (Phantom Omni). We conducted a between-subject user study experiment with four conditions (2D monitor with no guidance, VR with no guidance, VR with constant, active guidance, and VR with scaffolded guidance) to evaluate their performance in terms of procedural memory, motor skills in VR, and skill transfer to real life. Our results showed that the scaffolded guidance offers the most effective transitioning from the virtual training to the real-life task - even though the VR with no guidance group has the best performance during the virtual training. These findings are critical for the industry and academy looking for safer and more effective training techniques, leading to better learning outcomes in real-life implementations. Furthermore, this work offers new insights into further haptic research in skill transfer and learning approaches while offering information on the possibilities of haptic-assisted VR training for complex skills, such as welding and medical stitching.

Kinesthetic illusions, which arise when muscle spindles are activated by vibration, provide a compact means of presenting kinesthetic sensations. Because muscle spindles contribute not only to sensing body movement but also to perceiving heaviness, vibration-induced illusions could potentially modulate weight perception. While prior studies have primarily focused on conveying virtual movement, the modulation of perceived heaviness has received little attention. Presenting a sense of heaviness is essential for enriching haptic interactions with virtual objects. This study investigates whether multi-point tendon vibration can increase or decrease perceived heaviness (Experiment 1) and how the magnitude of the effect can be systematically controlled (Experiment 2). The results show that tendon vibration significantly increases perceived heaviness but does not significantly decrease it, although a decreasing trend was observed. Moreover, the increase can be adjusted across at least three levels within the range of 350-450 g. Finally, we discuss plausible mechanisms underlying this vibration-induced modulation of weight perception.

In providing realistic texture scanning experiences, the recent concentric rotation mechanism contributed to its small form factor, but its realism was not validated compared with the typical uni-directional slip feedback. Therefore, we investigated differences in tactile perception between concentric rotation and uni-directional feedback by implementing SpinTexture, which rotates a textured disk in sync with users' scanning speed. We configured five distances between the centers of the fingerpad and the disk (0.00, 0.25, 0.50, 0.75, and 1.00 cm) and two materials (sandpaper and silk). We first established rotation gain functions to provide perceptually similar sensations to real texture scanning. In 2D (Study 2) and 3D object (Study 3) interaction scenarios, our results showed that scanning realism (Study 2, 3) and enjoyment (Study 3) were insignificantly affected by the different center distances while the sandpaper interaction rated higher realism than silk. Our study bridges the gap between uni-directional and concentric methods.

Digital touch refers to haptic technologies that deliver somatic sensations primarily via cutaneous mechanoreceptors, with additional involvement of deeper receptors (e.g., muscles and joints). Like all emerging technologies, its benefits must be balanced against potential risks. We explore ethical concerns for future digital touch technologies by analysing the distinctive physiology and function of the human somatosensory system. Much current research on digital touch focuses on active touch. However, we argue that most pressing ethical concerns emerge with passive touch, where touch stimuli are controlled by external agents. First, somatosensation is "always on". Haptic technologies such as alerting systems often make use of this sensory availability, although doing so potentially undermines our sensory autonomy-the right to control our own sensations. Second, users need transparency about who/what is touching them and why, necessitating clear consent mechanisms. Third, as touch directly connects us with our environment, haptics that alter this interaction pose significant epistemic challenges, potentially distorting a user's perception of reality. Our analysis raises critical questions about cultural norms, privacy of bodily sensation, bodily self-awareness, control, transparency, and epistemic procedures. We propose an ethical design framework for digital touch, comprising four simple questions to guide future development of digital touch systems.

Gesture control systems based on mid-air haptics are increasingly used in infotainment systems in cars, where they can reduce drivers' distractions and improve safety. However, studies on vibrotactile adaptation show that exposure to mechanical vibration impairs the perception of subsequent stimuli of the same frequency. Given that moving vehicles generate different types of mechanical noise, it is crucial to investigate whether mid-air ultrasound stimuli are also affected by mechanical adaptation. Here, we directly addressed this question by testing participants' perception of ultrasound stimuli both before and after exposure to different mechanical vibrations. Across two experiments, we systematically manipulated the frequency (Experiment 1) and amplitude (Experiment 2) of the adapting mechanical stimulus and measured participants' detection threshold for different ultrasound test stimuli. We found that low-frequency mechanical vibration significantly impaired perception of low-frequency ultrasound stimuli. In contrast, high-frequency mechanical vibration equally impaired perception of both low- and high-frequency ultrasound stimuli. This effect was mediated by the amplitude of the adapting stimulus, with stronger mechanical vibrations producing a larger increase in participants' detection threshold. These findings show that mid-air ultrasound stimuli are significantly affected by specific sources of mechanical noise, with important implications for their safe use in the automotive industry.

Despite advances in vibrotactile displays, most existing systems are limited in their ability to deliver calibrated, frequency-differentiated stimulation across multiple touch modes. This constrains our understanding of how supra-threshold frequency modulation influences tactile perception, particularly in dynamic, shape-based interactions. To address this gap, we introduce the PinArray-a novel hybrid haptic device featuring a 4 × 3 array of independently actuated pins capable of delivering vibrations from 0 to 300 Hz. The PinArray uniquely supports static, passive, and active touch conditions, enabling nuanced exploration of tactile shape encoding. We evaluated the device in a user study examining the perception of edge-like shapes generated via frequency pairings. Results show that specific combinations, especially those involving static and dynamic frequency pairs, significantly enhance shape recognition. These findings highlight the device's potential for advancing both perceptual research and the development of expressive tactile interfaces.

It has been known for some time that a perception of wetness can be elicited when the skin is in contact with a cold, dry surface, a phenomenon called illusory wetness. The critical feature of the illusion is the rate at which the skin cools. This paper focuses on understanding the variables that contribute to illusory wetness by initially determining the sensitivity of participants to the rate with which the skin is cooled and then examining how the perception of illusory wetness is affected by the thermal and material properties of the contact surface. In the first experiment, the method of constant stimuli was used to measure the difference threshold for the rate of cooling on the hand. The results showed that the threshold averaged 0.90 ${}^{\circ }$C/s at a reference value of 0.5 ${}^{\circ }$C/s and that wetness was perceived at an average cooling rate of 1.09 ${}^{\circ }$C/s. In the second experiment, participants rated the perceived wetness of five contact materials presented at four different surface temperatures. The results showed that temperature was the more critical variable in determining perceived wetness, and that the influence of material properties in this experiment related primarily to their effects on the heat transfer process.

Haptic wearables provide an intuitive human-machine interface to convey information through the sense of touch, which may have promising applications in guided breathing. In this paper, we detail the design and evaluation of three wearable prototypes (Vibration, Skin Drag, and Tapping) capable of administering discrete (individual, separate pulses and stimuli) and continuous (overlapping or uninterrupted stimuli) forms of linear haptic cycles with inspiration from slow, deep guided breathing. Characterization was performed to quantify and validate the performance of six haptic stimuli (discrete/continuous vibration, skin drag, and tapping). Devices were quantified with key metrics that described the applied stimuli and the dynamics of the wearable. A human subjects study (N=25), composed of two-cycle tracking tasks, was conducted to determine device performance and user aptitude. Results indicated consistent directional recognition across all six stimuli, but discrete stimuli performed better in spatial localization tasks. Although outperformed in tracking/localization tasks, continuous stimuli, especially skin drag, were described as the most apt and intuitive pairing to guided breathing. Findings highlight the potential of these linear haptic stimuli in a number of applications, including guided breathing, navigation, virtual immersion, and communication.

Rendering affective touch through haptic interfaces has gathered significant interest due to its ability to elicit emotional responses. Among various forms of affective touch, this study focuses on stroke stimuli. An illusory stroke stimulus is rendered using eight discrete Pneumatic Unit Cell (PUC) actuators on the left forearm. The study systematically investigates how rendering parameters-including the traveling speed of the illusory stroke, the stimulus onset asynchrony (SOA) of consecutive indentations, and indentation pressure-affect the perceived pleasantness and continuity of the stimulus. Results reveal that higher speeds significantly improved both pleasantness and continuity, with speed emerging as the most influential factor. In contrast, SOA has no significant effect on either perceived pleasantness or continuity. Indentation pressure shows a moderate impact on pleasantness, with high pressures reducing pleasantness but having no significant effect on continuity. Additionally, a positive correlation is observed between perceived pleasantness and continuity, underscoring the relevance of the continuity illusion created by sequential indentations with discrete actuators in evoking pleasant sensations. These findings demonstrate the potential of PUC actuators for creating affective touch stimuli and provide preliminary insights into the influence of rendering parameters on affective touch in human-machine and human-robot interactions.

Online retail is still mostly limited to the visual channel despite haptic interface technology advances. One potential strategy for overcoming the lack of touch in online retail is using pseudo-haptics: illusory haptic sensations resulting from manipulating the visual feedback of mouse or touchscreen interactions. Previous research used computer-generated graphics for pseudo-haptic experiences, while online retailers rely heavily on accurate photos of their products. Therefore, our study proposes a novel approach to designing pseudo-haptics using interactive photograph series together with mouse cursor gain modulations, called Pseudo-Haptic Photograph Interaction (PHPI). Unlike prior approaches that rely on simulated or stylized imagery, PHPI introduces pseudo-haptic effects through real photographic sequences of fabric motion, bridging the gap between visual realism and interactive haptic simulation. We conducted user studies on the perception of stiffness and weight to validate our approach. In experiment 1, we investigated the relation between the perception of weight and stiffness and increased or decreased gain of mouse movement. The study reveals a strong relation between mouse gain and perception. To test whether this corresponded to pseudo-haptic sensations, we performed experiment 2, in which actual fabrics had to be matched with those displayed through PHPI. We found a correlation between the haptically perceived weight and stiffness of fabrics, and their digital surrogate mediated by visual cues, confirming the potential of PHPI for multimodal experiences in online retail and other photographic presentations.

Vibration feedback is a widely used form of haptic feedback in stylus-mediated interaction with screens of mobile devices. To accurately and efficiently present haptic effects, it is important to investigate key design factors that influence vibrotactile perception. In this paper, we perform experiments using two actuators (linear resonant actuator and voice-coil actuator) to investigate the effect of pressing force on perceived intensity with various combinations of factors such as actuator orientation, frequency of the driving signals, baseline perceived intensity, and user's motion speed in the vibrotactile feedback of stylus-mediated interaction. The results show that in stationary condition when the actuator is placed with its long side perpendicular to the axis of the stylus, the larger the pressing force is, the weaker the perceived intensity is; when the actuator is placed with its long side parallel to the axis of the stylus, the perceived intensity increases slightly with increasing pressing force. Another experiment is conducted and shows that the perceived intensity is more uniform when the amplitude is dynamically changed with the variation of the pressing force. For the moving conditions, the changes in pressing force have almost no effect on the perceived intensity. The results provide knowledge about the perceived intensity of vibrations in the stylus-mediated vibrotactile rendering.

This paper investigates the notion of "Persuasive Vibrations", which showed that augmenting a person's speech with vibrotactile feedback could artificially increase persuasion. However, while the initial paper has shown the effect, the underlying reasons why vibrations enhance persuasion remain unknown. Through two different user studies, this paper aims to study how the underlying parameters of the vibratory feedback (e.g., frequency, amplitude, or audio-vibration synchronization) influence persuasion. The first study aimed to identify the parameters of vibrotactile feedback that can positively influence persuasion. The second study evaluated vibrotactile feedback that might impair the persuasive effect. In a nutshell, the first experiment suggests that the isolation of different properties of the vibratory signal could tend to provide higher persuasion compared to no vibratory feedback. A lower frequency at 100 Hz seems the most efficient way to generate a persuasive effect. In contrast, the second experiment suggests that some alteration of the vibratory signal ( e.g., latency) does not decrease the levels of persuasion compared to the no-vibration condition. All in all, the results suggest that using lower frequencies could have a better effect on persuasion. These results could serve as a basis for haptic design in applications like videoconferencing, virtual meetings, and training systems where supporting user speech is essential.

Palpation of arteries holds significant physiological importance. Existing pulse actuator designs intended to replicate the haptic sensations of palpation primarily focus on normal force interactions, often overlooking the shear forces generated by oscillations of the arterial wall during blood flow. This study aims to evaluate the normal, longitudinal, and transverse forces exerted by arteries through both theoretical and experimental analyses during palpation. The experimental validation features a pulse actuator-sensor system. The actuator component is a hydroelectromagnetic actuator, while the haptic sensing is performed by the Subblescope. The Subblescope measures arterial force feedback from both soft and hard artery models, as well as from the radial pulse in 18 human subjects. Mathematical analysis establishes the operational range of the sensor-actuator system as 0.005 N to 2.5 N. The force feedback from the simulation has been used for designing the total force generation by the actuator. The reactive force along the Z-axis varies between 19.3 mN to 500 mN, while the transverse and longitudinal forces along the Y and X axes range from 6.9 mN to 88.01 mN and 5.46 mN to 87.85 mN, respectively. The pulse-force map of the hard artery reveals higher three-dimensional force interactions compared to the soft artery. The hydroelectromagnetic actuator effectively generates both normal and shear forces during pulsatile flow. Future work will focus on developing training modules that replicate pulse haptics associated with various physiological conditions, such as diabetes.

In [1], Fig. 5 shows that the code was inadvertently plotted IT on the graphs labeled Percent Correct and vice-versa (with IT multiplied by 100 rather than the fraction of correct responses) for subplots (b)-(d). None of the statistics or other analyses were affected. It was simply a transcription error in generating the plots for this specific figure, with incorrect data assigned to each plot window in MATLAB. In the figure, you will note that effectively the top and bottom data in each subplot are swapped as shown.