Deep learning has led to strong performance in recognizing materials from touch signals, but it is often difficult to understand which parts of those signals drive a model’s decision. This thesis studies accurate and interpretable tactile material classification on the public SENS3 dataset using three dominant cue sources: thermal transients during static contact, deformation dynamics during pressing, and friction/vibration cues during sliding. An adjective-mediated pipeline that first predicts psychophysical rating distributions and then classifies materials is compared against a direct multimodal classifier that fuses modality-specific encoders. The direct multimodal model shows strong generalization, reaching 0.896 test accuracy across seven retained material classes. To better understand the learned decision process, Integrated Gradients was used as the main explanation method, combined with Temporal Saliency Rescaling for models with a single classification output. The resulting attribution maps were then summarized into contributions at the level of signal type, interaction phase or bin, and individual measurement channel. The resulting explanations reveal class-conditional cue usage aligned with interaction structure: transient thermal phases dominate for metal-like materials, pressing dynamics contribute strongly for compliant/textile-like classes, and sliding evidence concentrates in low-force regimes where friction and vibration cues are most informative. Overall, the results demonstrate that high-performing tactile material recognition can be combined with interpretable, physically grounded attribution summaries, improving trust in model decisions for haptic interfaces and embodied systems. ... Read more

This study investigates how the placement and excitation frequency of piezoelectric actuators embedded in a soft silicone haptic thimble influence displacement patterns on the human fingertip. A finite element model (HapThimb) was developed in COMSOL Multiphysics by extending the DigiTip (Serhat & Kuchenbecker, 2021) model with a 4 mm thick Ecoflex 30 layer and four tangentially acting actuators positioned on the bottom, front, and both sides of the fingertip. The model simulates both free and forced vibrations to identify resonance modes and actuator-specific deformation patterns.
Free vibration analysis revealed that the addition of the thimble significantly reduced natural frequencies, with the first eigenmode shifting from 103.5 Hz (bare finger) to 45 Hz (with thimble).
Moreover, the number of observed modes increased, reflecting the thimble’s contribution to the complex dynamic behaviour of the system. Forced vibration analysis across the frequency range of 1–260 Hz revealed that actuator location has a strong effect on both the amplitude and spatial distribution of displacements. The bottom actuator yielded the highest local response (53.8 μm at 185 Hz), while the front actuator produced weaker, and localised responses. The side actuators, activated in-phase, resulted in the broadest and most versatile vibrational patterns, exciting multiple finger regions with peaks up to 41.4 μm. These findings highlight the importance of actuator placement in achieving desired tactile effects. The results inform design strategies for wearable haptic devices by identifying configurations that maximise vibrational efficiency and spatial selectivity. ... Read more

Generative AI has revolutionized domains such as language, vision, and audio; yet, its application to the field of haptics, specifically signals for friction modulation devices, remains barely explored. A generative model could alleviate the issues associated with recording friction-based texture signals, such as the expenses of recording equipment and the limitation to lab environments, which significantly constrain the diversity of texture signals that can be rendered on friction modulation haptic devices. We propose a generative latent diffusion model called DreamTexture. The model is conditioned on a feature vector derived from a psychophysical perceptual space, where each dimension corresponds to an adjective pair (e.g., Rough–Smooth, Sticky–Slippery). We investigate whether DreamTexture can synthesize friction signals that align with users’ perceptual expectations, despite the subjective nature of tactile experiences, influenced by individual skin properties and linguistic interpretation. Moreover, DreamTexture is optimized for real-time inference on commercially available hardware, making haptic content creation more scalable and accessible. Our findings indicate that the diffusion process lends itself well to the efficient generation of one-dimensional friction signals and produces realistic signals, but it exhibits limitations in fully capturing the variability inherent in the input space. ... Read more

With the growing popularity of virtual and augmented reality, there is an increasing demand for haptic devices that can replicate naturally occurring tactile sensations. Specifically, multimodal devices capable of delivering multiple types of haptic feedback simultaneously are crucial for enhancing realism and immersion. In this paper, we introduce a novel, entirely soft, multimodal haptic ring designed to provide vibratory, pressure, and thermal stimuli. Our ring, targeted for texture rendering applications, integrates pneumatic and hydraulic circuits to accurately simulate the roughness, temperature, and compliance cues experienced when freely exploring surfaces with the fingertip. We validated the performance of our system through a psychophysical experiment, which demonstrated that participants could match virtual textures displayed by the ring with real textures with up to 90 % accuracy for several surfaces. Participant’s adjectives ratings indicated that the ring can provide distinctly different stimuli in all of the rendered perceptual dimensions, closely matching those of real textures. This study shows that by relocating tactile feedback from the fingertip, our ring offers maximum wearability, enabling free exploration of surrounding environments and full range of motion, highlighting its potential in mixed reality applications. ... Read more

As virtual technology rapidly advances globally, the integration of the sense of touch into virtual environments to enhance realism is becoming increasingly urgent, drawing significant attention from scientists and researchers. This has led to the development of innovative haptic devices designed to replicate tactile sensations, further immersing users in virtual experiences. However, despite significant research in this field, most of the current haptic devices appear to lack the ability to provide direct, flexible, and natural interactions. To address these challenges, this study introduces the FlexCube, a novel flexible multimodal haptic display capable of delivering three tactile sensations: softness, roughness, and temperature. The FlexCube is developed through the creation of two modules—a hydraulic-actuated module for temperature and contact area rendering and a roughness module using the electrovibration effect. Then, they are combined together and integrated with an available stiffness rendering device into one device - the complete FlexCube. Subsequent experiments were conducted to evaluate the performance and behavior of each module individually. The results demonstrate that the FlexCube is capable of rendering a step profile and real texture’s temperature profile, tracking a sinusoid contact area profile of 0.2 Hz with neglectable delay, and able to deliver salient roughness sensations with the maximum generated electrovibration force of 0.028N regardless of the possible surface deformation. Overall, the FlexCube can simultaneously deliver all the expected tactile sensations and appears to be a promising tool for applications in E-commerce, telepresence, and interactive simulations. ... Read more

Minimally invasive medical procedures often require catheters, endoscopes and other devices to maintain position at a specific site in the body, to cut and remove tissue or for diagnostic purposes. Due to tool force exerted by the surgeon or the natural processes of the body, such as the activity of the heart or the lungs, the inserted device can dislodge or migrate from its intended location. Existing solution focus on stabilizing the tip, following high localized pressure, this can create tissue damage or even perforation. Hence, it can be beneficial to create stabilization over the full length of the catheter. I investigated the use of electroadhesion i.e. using electricity to adhere to the tissue wall. I created a scaled-up, flexible, electroadhesion stabilization proof of concept, consisting of two opposite-charged electrodes in a helical pattern, embedded in silicone rubber. Friction experiments were performed on the catheter proof of concept on two copper half-tube substrates. One of the three flexible scaled-up catheter samples showed an increase in the average dynamic friction coefficient of 10.2% between 0 and 2500 V for the 22 mm diameter substrate. The two other samples showed no or limited increase in friction, attributable to manufacturing differences. Predicting coating thickness is essential, as the coating is the determining factor for the performance of the electroadhesion device. The catheter showed potential, however, improved adhesion performance is required for feasibility on a smaller scale. ... Read more

Relocated haptic feedback from the fingertip to the proximal phalanx can alter the perception of physical interactions by simultaneously displaying relocated multimodal tactile cues. However, how these relocated tactile cues alter the vibrotactile sensitivity of the fingertip remains unclear. This two-site stimulation study employs a customdesigned multimodal haptic ring for the proximal phalanx to evaluate the effect of relocated cold, hot, and pressure stimuli on the vibrotactile sensitivity of the fingertip. Our results show no significant difference between the vibratory detection thresholds of six multimodal tactile conditions. In contrast to single-site multimodal stimulation, where vibrotactile sensitivity is significantly altered by pressure and thermal stimuli, these results imply the feasibility of applying thermal and pressure stimuli without significantly altering fingertip sensitivity. Relocation of tactile stimuli keeps the vibrotactile sensitivity of the fingertip intact and opens up the possibility of altering tactile perception while interacting with the physical environment, making this technology feasible for mixed reality applications. ... Read more

Glaucoma impacts vision by affecting visual processing at the retinal ganglion cell level. To recreate its impact on visual processing, photobleaching has been proposed to reversibly and temporarily induce glaucoma-like saccadic reaction time. It has been established that photobleaching elevates the threshold detection levels of visual stimuli in a healthy retina. This study investigated the potential implementation of photobleaching to recreate glaucoma-like SRTs. Results from the study show that photobleaching increased the SRT and reduced the ability to detect targets within the photobleaching zone of the visual field. The elevated SRTs obtained from the study indicate that photobleaching is a valid method for obtaining mild glaucoma-like SRTs. Furthermore, the effects of photobleaching were found to be highly localized, with the impact primarily observed within the bleaching zone. Attempts to replicate the localized effects of glaucoma using discrete photobleaching were inconclusive, with elevated SRTs observed in some cases, but the effect is directly related to the total area bleached. These findings provide the relationship between photobleaching, saccadic response, and their potential implications for artificially recreating glaucoma-like elevated SRTs ... Read more

Navigating touchscreens in vehicles becomes increasingly challenging when subjected to external perturbations like air turbulence or bumpy roads. These perturbations can lead to a loss in task performance, reduced finger accuracy, and increased frustration among users. To address these issues, electrovibration has emerged as a promising technology to enhance touchscreen interactions by providing users with better feedback and maintaining touch stability even under challenging conditions. Before we investigate if electrovibration helps users in challenging conditions, first the effects of external perturbations on tactile perception by electrovibration must be found. To investigate the impact of external perturbations on electrovibration perception, we conducted psychophysical experiments with 18 participants interacting with an electrostatic display mounted on the cockpit of the SIMONA flight simulator. We measured participants’ absolute detection thresholds for electrovibration pulses generated using 100 Hz input voltage for durations of 0.2 and 0.5 seconds, simulating a ridge and a button or slider. The measurements were taken under no-turbulence conditions and two different turbulence conditions. Our results revealed that turbulence significantly affects vertical finger movement, average normal force, and the change in force applied to the screen by participants. This combination of factors, along with the 0.2-second pulse duration, makes electrovibration more difficult to perceive or even imperceptible. The 0.5-second electrovibration pulse was perceived better overall and remained unaffected by turbulence. This highlights the strong significance of pulse duration on the absolute threshold of electrovibration. Therefore, to counteract the negative effects of perturbations on perception, electrovibration should be employed for longer durations when perturbations are present. ... Read more

The provision of somatosensory information may play a fundamental role in the recovery of stroke patients. Particularly, tactile information is known to influence motor control by contributing to the perception of the weight, friction, and slip condition of objects. Despite this, the inclusion of tactile information through haptic rendering in robotic neurorehabilitation systems remains largely unexplored. In this study, we present a tactile interface to extend the kinesthetic rendering capabilities of an existing hand rehabilitation robot. The developed solution relies on skin stretch stimulation of the fingerpads, which allows the rendering of interaction forces with tangible virtual objects, e.g., friction, weight, and inertia. In contrast with previous skin stretch devices, our system uses closed-loop force control for accurate force rendering, relying on a custom magnetic field-based three-axis force sensor. A three-axis positioning stage in combination with a reference force sensor was used for calibrating and characterizing the sensor, as well as evaluating the interface response. The sensor achieves shear force accuracies of 0.2 N, influenced by hysteresis and viscoelastic creep effects. The tactile interface achieves a steady-state error of 0.2–0.4N and rise times of 20–70 ms during step response tests. Frequency response tests show that the interface can successfully track signals up to 5–7 Hz. The novel use of force-controlled skin stretch stimulation aims to open a new avenue for the accurate rendering of interaction forces through the tactile sense. Moreover, through purposeful design for usage in the rehabilitation domain, we hope that this study will serve as a stepping stone toward the inclusion of tactile information in robot-assisted therapies. ... Read more

The emergence of tactile technologies has paved the way for addressing various challenges. Tactile sensing is especially vital for the blind and visually impaired. This study investigates how tactile feedback can enhance mobility and independence among individuals in this community. In today’s touchscreen-dominated world, accessibility remains a critical concern for those who are visually impaired, as touchscreens lack the tactile guidance necessary for effective touchscreen use. In addition, it is investigated if the guidance is useful for orientation. Our innovative approach employs a directional friction modulation rendering method, aiding users in finger movement and orientation. The efficacy of the tactile directional cue will be assessed for a tracking task and an orientation task. The tactile cue’s shape is determined by the parameter σ, which we optimize in our research. Additionally, in the orientation experiment, we explore the impact of different Field of Feeling ranges, representing the maximum perceivable angles on the actuated glass plate. Our methodology involves blindfolded participants in experiments assessing their ability to interpret and respond to tactile cues generated by an ultrasonic friction modulation device. We use quantitative measures, including response time and directional accuracy, and qualitative feedback from questionnaires to capture participants’ experiences with the tactile feedback system. Our findings reveal fascinating insights into the influence of σ and the Field of Feeling. On average the paths were tracked with an error of 9.84 mm. Smaller σ values correlate with improved tracking performance, as evidenced by the lower root-mean-square error between the finger and the reference path. This relationship is described using a logistic function. The directional friction modulation rendering method was shown to be viable for finding the reference angle. On average, this was achieved in 10.79 seconds with a manageable error of 6.28 ◦ . Specific differences between the tested values for σ were not found. In contrast, the Field of Feeling’s influence on the results appears more pronounced. A broader Field of Feeling leads to quicker decision times when at the reference angle. These outcomes shed light on the feasibility and effectiveness of ultrasonic friction modulation as a tactile feedback mechanism for enhancing the independence of blind individuals. Furthermore, the successful integration of this technology holds the potential to revolutionize electronic surface haptic devices for a wide range of users. ... Read more

Electrovibration offers potential to enrich virtual touch experiences with authentic tactile sensations on touchscreens. In controlled environments, responses to tactile stimuli may be anticipated, yet this predictability becomes uncertain in unconstrained settings due to dynamic factors like varied applied force, finger scanning speed, and sensory adaptation. To address this issue, we conducted a psychophysical study with 21 participants to investigate the effect of tactile
rendering parameters on user exploratory behaviour and perception during unconstrained exploration of artificial textures, aiming to discern a predominant tendency of interaction. Our results revealed, signal amplitude shapes human tactile
perception considerably during unconstrained exploration. We also observed, higher signal amplitudes were associated with lower finger scanning speeds, a trend tempered by significant individual differences, thereby affecting its practical effect. In contrast, the measured applied normal force and obtained finger movement pattern remained consistent and were not affected by different tactile rendering parameters. Notably, the rate of change of measured lateral force was found
to be a better metric for the perceived tactile dimensions than the lateral force magnitude. These findings enhance our understanding of perception and physics of such interactions, that could be vital for designing and delivering improved
haptic feedback on electrovibration-based tactile interfaces. ... Read more

Thermal feedback has been proven to enhance the user experience in human-machine interaction. However, state-of-the-art technology mainly focuses on static contact using either palm or fingertip, overlooking dynamic and multi-finger interactions. Underlying challenges include incompatible designs of the conventional interfaces for providing controllable salient thermal stimuli for such interactions and, thereby, lack of knowledge on human thermal perception for relevant conditions. Here we designed a new thermal display that can deliver distributed spatio temporal thermal patterns and investigated the influence of user exploration on the perception of these patterns. Twenty-three human participants interacted with the device using three exploration conditions (static-single finger, dynamic-single finger, and static-multi finger) and evaluated 15 temperature differences ranging from +1.5◦C to -7.5◦C. Our results showed that humans are significantly more sensitive to thermal stimuli when exploring via static single-finger contact than other tested conditions. Moreover, in the case of static-single finger interaction, we found larger thermal discrimination thresholds compared to the literature. Our findings offer new perspectives on providing salient and consistent thermal feedback for future tactile interfaces. ... Read more

The ever-emerging mobile market induced a blooming interest in stylus-based interactions. However, most state-of-the-art styli are passive or display only unimodal tactile feedback. Multimodal haptic devices that simultaneously stimulate our cutaneous and kinesthetic receptors to provide immersive and realistic sensations in a virtual environment during touchscreen interactions are highly desired. To this end, we developed FeelPen, a novel handheld multimodal haptic interface for touchscreens, incorporating various actuators in a smartly designed way. A voice-coil actuator, placed along the stylus tip, simulates object compliance by modifying its stroke force. Electrovibration, generated between the stylus tip and a capacitive screen, delivers roughness and stickiness cues. In addition, temperature feedback on the fingertip is provided by a miniature thermal module. We conducted characterization experiments to determine the physical characteristics and limitations of the device, followed by a psychophysical experiment, where the perceptual dimensions of the device were extracted using the semantic differential method on a set of artificial textures. Our results revealed four tactile dimensions, with the first two related to texture surface properties, and the third and fourth dimensions linked to material softness and coldness, respectively. FeelPen opens up new dimensions for future realistic texture rendering on touchscreens. ... Read more

Vibrotactile wearable devices are a non-intrusive and inexpensive means to provide haptic feedback directly on the user’s skin. These devices utilize one or multiple vibrotactile actuators to generate vibrations across the skin and into the tissue. Combining these vibrations in amplitude can create the illusion of a funneled sensation on the skin at another location than at the actual sites of stimulation. This allows for the placement of virtual actuators on the skin, such that fewer actuators need to be deployed. However, the illusion does not take into account that the waves originating from the actuator attenuate and disperse due to the viscoelastic properties of the skin. We hypothesize that this diffusion of the elastic energy in the skin is affecting the perception of this illusion. Therefore, if we correct for the wave propagation speed, and temporally focus the stimulation, we hypothesized that the specificity of the stimulation on the skin could be drastically improved. In this paper, a novel technique, which is named the inverse filter technique, was introduced that enables to focus the amplitude, frequency and phase of vibrations to one location while cancelling them at the remaining nearby positions. We developed a wearable device for the volar surface of the forearm on which we could independently control arbitrary waveforms at any position between a set of four physical actuators. A human-subject study found that the performance in terms of localization confidence was improved significantly, whereas the precision and accuracy of the task did not improve compared to when we did not correct for the wave attenuation and dispersion. These results show that focusing waves towards a target location has a direct influence on our confidence of localizing vibrotactile stimuli on the arm. Therefore, we anticipate that our findings can benefit industries interested in including localized vibrotactile feedback on the human body surface. ... Read more