Abstract Dynamic touch requires the perceptual system to extract stable material properties from complex, evolving signals. We show that the tactile system relies on total spectral energy, the overall vibratory power of contact-induced transients, rather than waveform details or dominant frequency. Using a spectral energy compensation method, we conducted five psychophysical experiments in two degraded feedback scenarios: soft finger interfaces, where fingertip stiffness was reduced by an inflatable silicone bubble, and soft surface interactions, where participants tapped compliant foam surfaces. In both, participants reliably discriminated hardness and identified materials only when natural spectral energy profiles were preserved, independent of signal type. Judgments scaled systematically with energy level, and under conflicting cues, spectral energy dominated over frequency or compliance. These findings establish spectral energy as a governing cue in tactile perception, revealing a simple and robust computation akin to estimating mechanical work. This principle offers a generalizable framework for restoring touch in prosthetics, teleoperation, and immersive virtual environments. Teaser Total spectral energy - not frequency - is the behaviorally relevant feature driving material perception through dynamic touch.

Vision and sound often dominate human–robot interaction systems, but touch can convey nuanced, real-time task and environment information. Vibrotactile feedback is increasingly common in commercial devices, and the wrist offers a promising location for wearable haptics: it is unobtrusive and sensitive to tactile input. While prior work has studied vibrotactile feedback in navigation and action confirmation tasks, quantifying information transfer for wrist-worn vibrotactile cues remains underexplored. This study estimates information transfer on the wrist (bits per stimulus) using a confusion-matrix-based metric alongside accuracy and pleasantness ratings. We conducted three linked studies with the same participants: identifying single-tactor cues spanning frequency, amplitude, and modulation; identifying the same cues under sequential vibrotactile masking and during a concurrent typing task; and identifying multi-tactor spatiotemporal patterns and rating pleasantness. Participants reliably discriminated complex signals, with amplitude and feature interactions playing key roles. Information transfer ranged from 0.75 bits/stimulus for multi-tactor patterns to 2.28 bits/stimulus for single-tactor testing across all participants (2.56 for experienced participants); masking and typing yielded 1.64 and 1.85 bits/stimulus, respectively. Performance was not solely driven by amplitude-normalized intensity.

We investigated whether surface texture (i.e., stochastic roughness) influences softness perception during direct touch interactions with elastic, textured stimuli. Using a Bayesian adaptive modeling approach and a 2AFC task, we evaluated participants' ability to discriminate the softness of stimuli that varied in both their stochastic surface roughness (Hurst exponent) and material elasticity. To explore potential interactions between these features, we conducted two discrimination experiments, testing stimuli from two distinct ranges of elasticity. All participants performed the task using pressing. Results show that softness discrimination was determined primarily by material elasticity, with no discernible influence of surface features. The findings suggest that humans effectively isolate elasticity-based information from smaller-scale surface topography or texture during direct pressing with the finger.

Roughness perception is a fundamental dimension of touch that guides object recognition and manipulation. While perceived roughness is typically attributed to surface texture, realworld materials rarely vary in texture alone–they also differ in material properties such as elasticity. Whether material properties contribute to roughness perception, and how they might interact with surface cues, remains poorly understood. Here, we investigated how texture and elasticity jointly influence perceived roughness by parametrically varying both features within a Bayesian optimization discrimination task. Participants compared pairs of stimuli differing in stochastic surface roughness and material elasticity, under both direct and tool-mediated touch. This approach enabled us to estimate two-dimensional perceptual functions and identify haptic roughness metamers–physically distinct stimuli perceived as equally rough. These perceptual equivalences were mirrored in confidence ratings and varied systematically with the relative stiffness between the stimulus and the probing tool or finger, implicating contact-induced vibrations as a mediating factor. Our findings reveal how texture and elasticity cues jointly constrain roughness perception, demonstrating that perceived roughness emerges from the integration of multiple stimulus dimensions rather than surface properties alone. These findings offer practical implications for the design of haptic interfaces and prosthetics, where equivalent percepts may be achieved through different combinations of material and texture, and contribute to a broader understanding of cue integration in haptic perception. Significance Statement Human touch perception must contend with ambiguity from varying tools, materials, and contexts. This study reveals that perceived roughness arises not from surface texture alone, but from the integration of texture and material elasticity–two physical cues that can trade off to produce indistinguishable tactile roughness percepts. These “roughness metamers” emerge even when touch is mediated through a probe, underscoring the role of vibratory cues, but their emergence depends on the relative stiffness between probe and surface. This finding expands how we understand roughness perception and has direct implications for the design of artificial limbs, robotic sensing, and haptic interfaces that aim to recreate natural tactile experiences. ### Competing Interest Statement The authors have declared no competing interest.

Tactile surface perception is often assumed to reflect a fixed boundary between body and world, with the skin providing a stable oriented surface that separates inside from outside. We show that this assumption fails in functionally specific ways. Using moving tactile stimuli on the hand, participants perceived stimulus direction on the fingertips as reversed when hand posture changed - reporting motion as if it originated from the opposite side of the skin, while responses on the palm were less consistent and less sensitive to posture. Congenitally blind participants exhibited stable, individualized surface assignments on the fingertips, demonstrating that vision is not required to construct oriented tactile surfaces. However, visual experience modulated posture effects: sighted individuals showed posture-dependent, skin-orientation assignments driven by motion direction, whereas congenitally blind individuals showed posture-invariant assignments determined by functional use. These findings indicate that tactile surface perception is not globally fixed but dynamically inferred according to functional demands; rather than enforcing a purely geometric body-world boundary, the brain flexibly assigns where the surface is and which side we occupy. ### Competing Interest Statement The authors have declared no competing interest. Fondation Fyssen, https://ror.org/05ebnp485 Agence Nationale de la Recherche, https://ror.org/00rbzpz17, ANR-16-CE28-0015 Leverhulme Trust, https://ror.org/012mzw131, VP1-2016-060)

We present a technique for providing remote tactile feedback to the thumb and index finger via a wristband device. This enables haptics for touch and pinch interactions in mixed reality (MR) while keeping the user's hand entirely free. We achieve this through a novel cross-modal stimulation, which we term visually augmented electro-tactile feedback. This consists of (1) electrically stimulating the nerves that innervate the targeted fingers using our wristband device; and (2) concurrently, visually augmenting the targeted finger in MR to steer the perceived sensation to the desired location. In our psychophysics study, we found that our approach provides tactile perception akin to tapping and, even from the wrist, it is capable of delivering the sensation to the targeted fingers with similar to 50% of sensation occurring in the thumb and similar to 40% of sensation occurring in the index finger. These results on localizability are unprecedented compared to electro-tactile feedback alone or any prior work for creating sensations in the hand with devices worn on the wrist/arm. Moreover, unlike conventional electro-tactile techniques, our wristband dispenses with gel electrodes. Instead, it incorporates custommade elastomer-based dry electrodes and a stimulation waveform designed for the electrodes, ensuring the practicality of the device beyond laboratory settings. Lastly, we evaluated the haptic realism of our approach in mixed reality and elicited qualitative feedback from users. Participants preferred our approach to a baseline vibrotactile wrist-worn device.

It is known that human haptic perception is lateralised, for example, object shape is felt differently according to the hand used to explore objects. Here we show that it is not the hand but the hemispace in which the exploring hand is located that determines differences in perception. This finding implies that our lateralised somatosensory processing depends on hand localisation in space rather than on the hand itself. ### Competing Interest Statement The authors have declared no competing interest.

Understanding the interplay between surface roughness and material elasticity in haptic texture perception is important. In the real world, these characteristics do not occur isolated from one another, yet, the haptic perceptions of surface features and material properties are often investigated individually. This highlights the need for suitable stimulus material for haptic perceptual experiments. The present research details the manufacturing and validation of a database of stochastically-rough, elastic stimuli tailored for haptic perceptual experiments. The stimulus set comprises 49 3D-printed samples, offering a systematic variation in stochastic microscale roughness and material elasticity, replicating natural surface features without compromising experimental control. The surfaces were generated using an algorithm that produces randomly rough surfaces with well-defined spectral distributions, demonstrating fractal properties over a large range of length scales. Controlled variations in elasticity were implemented via variations of the printing material composition. Finally, we present preliminary perceptual data from two observers, illustrating the discriminability of the stimulus space for roughness and softness discrimination. This database aims to facilitate haptic research on material and texture perception, offering a controlled yet naturalistic set of stimuli to explore the intricate interplay between surface roughness and material elasticity in shaping haptic texture perception.

In this paper, we investigate postural reinforcement haptics for mid-air typing using squeeze actuation on the wrist. We propose and validate eye-tracking based objective metrics that capture the impact of haptics on the user's experience, which traditional performance metrics like speed and accuracy are not able to capture. To this end, we design four wrist-based haptic feedback conditions: no haptics, vibrations on keypress, squeeze+vibrations on keypress, and squeeze posture reinforcement + vibrations on keypress. We conduct a text input study with 48 participants to compare the four conditions on typing and gaze metrics. Our results show that for expert qwerty users, posture reinforcement haptics significantly benefit typing by reducing the visual attention on the keyboard by up to 44% relative to no haptics, thus enabling eyes-away behaviors.

Temporal binding refers to a systemic bias in the perceived time interval between two related events, most frequently voluntary motor actions and a subsequent sensory effect. An inevitable component of most instrumental motor actions is tactile feedback. Yet, the role of tactile feedback within this phenomenon remains largely unexplored. Here, we used local anesthesia of the index finger to temporarily inhibit incoming sensory input from the finger itself, while participants performed an interval-estimation task in which they estimated the delay between a voluntary motor action (button press) and a second sensory event (click sound). Results were compared to a control condition with intact sensation. While clear binding was present in both conditions, the effect was significantly enhanced when tactile feedback was temporarily removed via local anesthesia. The results are discussed in light of current debates surrounding the underlying mechanisms and function of this temporal bias.

Fingertips are one of the most sensitive regions of the human body and provide a means to dexterously interact with the physical world. To recreate this sense of physical touch in a virtual or augmented reality (VR/AR), high-resolution haptic interfaces that can render rich tactile information are needed. In this paper, we present a wearable electrohydraulic haptic interface that can produce high-fidelity multimodal haptic feedback at the fingertips. This novel hardware can generate high intensity fine tactile pressure (up to 34 kPa) as well as a wide range of vibrations (up to 700 Hz) through 16 individually controlled electrohydraulic bubble actuators. To achieve such a high intensity multimodal haptic feedback at such a high density (16 bubbles/${\mathrm{cm}}^{2}$) at the fingertip using an electrohydraulic haptic interface, we integrated a stretchable substrate with a novel dielectric film and developed a design architecture wherein the dielectric fluid is stored at the back of the fingertip. We physically characterize the static and dynamic behavior of the device. In addition, we conduct psychophysical characterization of the device through a set of user studies. This electrohydraulic interface demonstrates a new way to design and develop high-resolution multimodal haptic systems at the fingertips for AR/VR environments.

Mid-air haptics allow bare-hand tactile stimulation; however, it has a constrained workspace, making it unsuitable for room-scale haptics. We present a novel approach to rendering mid-air haptic sensations in a large rendering volume by turning a static array into a dynamic array following the user's hand. We used a 6DOF robot to drive a haptic ultrasound array over a large 3D space. Our system enables rendering room-scale mid-air experiences while preserving bare-hand interaction, thus, providing tangibility for virtual environments. To evaluate our approach, we performed three evaluations. First, we performed a technical system evaluation, showcasing the feasibility of such a system. Next, we conducted three psychophysical experiments, showing that the motion does not affect the user's perception with high likelihood. Lastly, we explored seven use cases that showcase our system's potential using a user study. We discuss challenges and opportunities in how large-scale mid-air haptics can contribute toward room-scale haptic feedback. Thus, with our system, we contribute to general haptic mid-air feedback on a large scale.

Haptic feedback is known to enhance the realism of an individual's interactions with objects in virtual environments. Wearable haptic devices, such as vibrotactile sleeves or armbands, can provide haptic feedback in a smaller and more lightweight form factor than haptic gloves that can be bulky and cumbersome to the wearer. In this article, we present tactile and squeeze bracelet interface (Tasbi), a multimodal haptic wristband that can provide radial squeeze forces around the wrist along with vibrotactile feedback at six discrete locations around the band. Tasbi implements a squeezing mechanism that minimizes tangential forces between the band's points of contact with the skin, instead of focusing the motor actuation to predominantly normal forces. Force sensing capacitors enable closed-loop control of the squeeze force, while vibration is achieved with linear resonant actuators. A detailed description of the design and experimental results demonstrating closed-loop control of squeeze cues provided by Tasbi is presented. Additionally, we present the results of psychophysical experiments that quantify user perception of the vibration and squeeze cues, including vibrotactile identification accuracy in the presence of varying squeeze forces, discrimination thresholds for the squeeze force, and an analysis of user preferences for squeeze actuation magnitudes.

Social touch is essential for creating and maintaining strong interpersonal bonds amongst humans. However, when distance separates users, they often rely on voice and video communication technologies to stay connected with each other, and the lack of tactile interactions between users lowers the quality of the social interactions. In this research, we investigated haptic patterns to communicate five tactile messages comprising of four types of social touch (high five, handshake, caress, and asking for attention) and one physiological signal (the pulse of a heartbeat), delivered on the hand through a haptic glove. Since social interactions are highly dependent on their context, we conceived two interaction scenarios for each of the five tactile messages, conveying distinct emotions being spread across the circumplex model of emotions. We conducted two user studies: in the first one participants tuned the parameters of haptic patterns to convey tactile messages in each scenario, and a follow up study tested naïve participants to assess the validity of these patterns. Our results show that all haptic patterns were recognized above chance level, and the well-defined parameter clusters had a higher recognition rate, reinforcing the hypothesis that some social touches have more universal patterns than others. We also observed parallels between the parameters' levels and the type of emotions they conveyed based on their mapping in the circumplex model of emotions.

Ultrasound mid-air haptic (UMH) devices are a novel tool for haptic feedback, capable of providing localized vibrotactile stimuli to users at a distance. UMH applications largely rely on generating tactile shape outlines on the users’ skin. Here we investigate how to achieve sensations of continuity or gaps within such two-dimensional curves by studying the perception of pairs of amplitude-modulated focused ultrasound stimuli. On the one hand, we aim to investigate perceptual effects that may arise from providing simultaneous UMH stimuli. On the other hand, we wish to provide perception-based rendering guidelines for generating continuous or discontinuous sensations of tactile shapes. Finally, we hope to contribute toward a measure of the perceptually achievable resolution of UMH interfaces. We performed a user study to identify how far apart two focal points need to be to elicit a perceptual experience of two distinct stimuli separated by a gap. Mean gap detection thresholds were found at 32.3-mm spacing between focal points, but a high within- and between-subject variability was observed. Pairs spaced below 15 mm were consistently (>95%) perceived as a single stimulus, while pairs spaced 45 mm apart were consistently (84%) perceived as two separate stimuli. To investigate the observed variability, we resort to acoustic simulations of the resulting pressure fields. These show a non-linear evolution of actual peak pressure spacing as a function of nominal focal point spacing. Beyond an initial threshold in spacing (between 15 and 18 mm), which we believe to be related to the perceived size of a focal point, the probability of detecting a gap between focal points appears to linearly increase with spacing. Our work highlights physical interactions and perceptual effects to consider when designing or investigating the perception of UMH shapes.

Vibrotactile feedback is increasingly common in wearable wristband devices. While much work has explored specific mappings in navigation and guidance tasks and to close the action-confirmation loop during interactions, little has focused on evaluating the communication capacity of the wrist and how it improves everyday interactions and tasks. To study these questions, we used information transfer as a metric to explore the space of signal variations within a single vibrotactile actuator (e.g., frequency, amplitude, and modulation). We ran a user study with the salient haptics cues to determine how well people were able to identify them without training on the dorsal side of the wrist, if they could interpret them better with training, and if that knowledge could be transferred to a secondary, untrained location (volar side of the wrist). Our results suggest that people are able to interpret at least 5 of the 8 cue variations, and are better able to recognize vibrotactile signals with training. We discuss the implications of the results for enabling vibrotactile interactions on the wrist.

The open access EuroHaptic 2020 proceedings volume is dealing with human haptic sensing and touch enabled computer applications. This year the conference focusses is on accessibility and papers deal with haptic science, haptic technology, and haptic applications.