There are individual differences in human tactile sensation, but it is not clear what causes these differences. One possible cause is the varying mechanical properties of the skin. To unravel this, we focused on the skin-propagated vibration characteristics and vibrotactile sensitivity. First, we measured the skin-propagated vibration of the fingertip for 28 participants and then conducted a cluster analysis to determine how the transfer function of the skin vibration differs among participants, estimating mechanical parameters based on the mechanical model. The results indicated that the transfer functions could be grouped according to the magnitude of the high-frequency gain. Subsequently, the detection thresholds for the 200 and 450 Hz vibrotactile stimulation were measured. The correlation analysis between the gain and the detection threshold showed a statistically significant correlation at 450 Hz. The results suggest that individual differences in human perception are influenced by the mechanical differences in the skin as well as the cognitive processing.
Thermal grill illusion (TGI) is a phenomenon involving a painful or burning sensation that is perceived when warm and cold stimuli are simultaneously placed on the skin. We proposed that the TGI can be generated by directly activating transient receptor potential channels, which contribute to temperature perception, with chemical substances such as capsaicin and menthol. This method enables the energy-saving and compact presentation of pain sensations. We examined the reactions of the study subjects to each chemical and then applied two chemicals to the same or adjacent parts of the skin to verify the generation of the TGI (n = 10, recruited from lab members). The results suggest that the application of capsaicin and menthol next to each other generates the TGI.
The stability and fidelity of haptic simulation systems have been studied for a safer and more faithful haptic interaction with virtual environments. The theoretical analysis, which use a second-order model for the actuator does not match well with the experimental results at high sampling rates. In this work, we propose more accurate models and analyze the uncoupled stability and fidelity for a system actuated by a permanent magnet DC motor and its voltage driver when implementing a linear viscoelastic environment. Through theoretical work and experiments, we show that the stability and fidelity of the system are more accurately represented when a high-order dynamic model is used for the motor and its driver.
This paper proposes a pulley-based haptic simulator device as training tool for ureteroscopy allowing for continuous insertion into a virtual ureter. The device motor provides a resistive feedback force to familiarize users with the forces experienced during surgery. We conducted a preliminary evaluation study with 7 subjects to compare subject performance using the system with visual and visuo-haptic feedback. Results support the utility of the device in terms of range forces rendered to the user and accurate following of the ureter profile. The addition of haptic feedback caused the subjects to perform the task more slowly. Future studies will evaluate if haptic feedback leads to enhanced skill development long-term with extended practice.
While many factors shape the preferential use of our hands, there is growing evidence that each hand may also perceive the environment differently. Currently, this has been demonstrated for proprioceptive and cutaneous cues, but our understanding of perceptual asymmetries for kinesthetic cues like stiffness is limited. In this manuscript, we measured JNDs of N=14 participants in an active stiffness discrimination task using their left and right hand. We found significant perceptual asymmetries between the two hands with left hand exploration leading to lower JNDs. Further investigation is needed, however, to understand the potential role of handedness in the observed perceptual asymmetries.
Haptic feedback in virtual reality (VR) allows users to perceive the physical properties of virtual objects (e.g., their weight and motion patterns). However, the lack of haptic sensations deteriorates users' immersion and overall experience. In this work, we designed and implemented a low-cost hardware prototype with liquid metal, VibroWeight, which can work in complementarity with commercial VR handheld controllers. VibroWeight is characterized by bimodal feedback cues in VR, driven by adaptive absolute mass (weights) and gravity shift. To our knowledge, liquid metal is used in a VR haptic device for the first time. Our 29 participants show that VibroWeight delivers significantly better VR experiences in realism and comfort.
We present an exploration of electrovibration beyond the fingertip. We first explored the design space and feasibility of electrovibrating clothing and wearables, before pivoting to its use on rigid objects that our palms frequently brush against. We then conceptualized and sketched an electro-vibrating keyboard that produces tactile feedback on the palms. To better understand the capabilities of this keyboard, we then conducted a psychophysical experiment with 14 participants to measure the detection thresholds of electrovibration at the palm and the fingertip. We found no statistically significant difference between the palm and fingertip, which suggests that the palm is an appropriate target for electrovibration.
In the cosmetics industry, an understanding of the meaning of skin sensory words in foreign language is of critical importance to facilitate the development of cosmetics that satisfy global consumers. Our previous study observed the possibility of cross-cultural differences in evoked haptic exploratory procedures (HEPs) between countries, specifically in relation to skin sensory words with the same lexical meaning. To explore these cultural differences in tactile sensory words of the skin, this study investigated mentally evoked HEPs in participants from five main markets for the cosmetics industry. We asked the participants for their mentally evoked HEPs, and then conducted principal component analysis on the results to understand the differences between the skin sensory words from the characteristics of components of mentally evoked HEPs. We found that the numbers and interpretation of the principal components were different across the five countries. The principal components of the HEPs were described as weight and direction (pressing or stroking). These findings confirm that there are skin sensory words with the same lexical meaning in different languages, which nevertheless evoke different mental HEPs and help decode cultural differences in tactile perceptions.
Design of products for pleasant or luxurious feeling is important within the consumer products industry, yet this is mostly still a trial-and-error activity. Friction reduction through texture is often the approach, yet the interface is complex due to multiphysical phenomena such as capillary bridges formed by sweat, deformation and contact as well as the textures ranging from macroscale to nanoscale on both surfaces. The universal existence of lipids and sebum makes the friction force and the tactile feeling of the textured surface more difficult to understand and predict by affecting the interface in different ways. In this work, a multiphysics model was employed to model and elucidate the underlying physics and mechanisms of the interface at the single asperity level.
Assuming the use scenario of free exploration on tactile graphics for people with visual impairments, this study investigated how the users perceive electrostatic friction stimuli on contour-based graphical information. We designed and conducted two experiments with 16 participants (8 visually-impaired and 8 sighted). First, we obtained spatial gap detection thresholds between two lines rendered using the electrostatic display. Second, we investigated spatial numerosity judgement on rendered lines on the display. Results demonstrated that the visually-impaired and sighted participants had similar perceptual performance. We summarize the findings and present suggestions for tactile graphics on an electrostatic friction display.
We present a wearable cutaneous device capable of applying lateral stretch and position/location haptic feedback to the user's skin. It is composed of a 2D Cartesian-like structure able to move a pin on the plane parallel to the skin. The pin houses a small metallic sphere of 8 mm of diameter. The sphere can be either left free to rotate when the pin moves, providing location feedback about its absolute position, or kept fixed, providing skin stretch about its relative displacement. The device weighs 30 g for a workspace of $12\times 12$ mm. This paper presents the device's design and actuation together with a perceptual evaluation of the position/location feedback provided by the device when worn around the forehead, forearm, and hand. Finally, we test the device in a preliminary human navigation task. Results show an average navigation error of 0.26 m, which is comparable to state-of-the-art vibrotactile guidance techniques using two vibrating armbands.
This work presents a large-scale texture classification method using a novel texture feature Projected Spectral Mapping (PSM) based on audio-tactile crossmodal congruence in unconstrained tool-surface interactions. We describe a quick-computable extraction process for PSM from the proposed crossmodal inter-band spectral mapping (IBSM) that relates the frequency components in different bands between the modalities. We conducted a texture classification on the LMT Haptic Texture Dataset with 69 textures in 9 categories to evaluate the PSM feature by both random sampling train-test split and participant-specific cross-validation. Compared to a variety of texture features from previous work, the results showed that our PSM feature reached >74 % classification accuracy by 3 out of 4 classifiers and outperformed all other features with significant improvement.
In Japanese language, onomatopoeia is used to describe perceptions such as the state of the skin and the feeling of touch. Although some studies have examined the relationship between onomatopoeia and physical properties expressing haptic sensation, few studies have examined the relationship between onomatopoeia and physical properties of flexibility. In this study, we aim to clarify the relationship between onomatopoeia and physical properties of soft objects. We asked subjects to describe the tactile sensations of 12 different silicone gels using onomatopoeia under three conditions: visual only, tactile only, and visuo-tactile. The range and number of phonetic occurrences of the onomatopoeia were extracted, and the relationship between onomatopoeia and physical properties was investigated. While we did not observe distinct differences in the range and number of onomatopoeic sounds under each condition, we observed differences in the types of onomatopoeia recalled due to differences in hardness under all conditions. In addition, regression results based on quantification theory class I showed that some of the explanatory variables of onomatopoeia (e.g., second mora contracted sounds and second mora vowels) change their significant contribution to the onomatopoeia depending on the change in conditions, even for a physical property.
Most studies of haptic illusions assume that the actuators used are identical and therefore produce vibrations with the same frequency. We ran two experiments to investigate the effect of mismatched vibratory frequencies on the perception of apparent tactile motion. We simulated having actuators with different properties by changing the frequency and amplitude of vibrations produced by a wideband actuator. We varied frequencies from 50 to 250 Hz with adjusted amplitudes to normalize the perceived intensity. The results suggest that the apparent tactile motion illusion is robust to mismatches in the resonant frequency of actuators and that it can therefore be produced by pairs of haptic devices with different specifications.
Design and optimization of vibrotactile codecs require precise measurements of the compressed signals' perceptual quality. In this paper, we present two computational approaches for estimating vibrotactile signal quality. First, we propose a novel full-reference vibrotactile quality metric called Spectral Perceptual Quality Index (SPQI), which computes a similarity score based on a computed perceptually weighted error measure. Second, we use the concept of Multi-Method Assessment Fusion (MAF) to predict the subjective quality. MAF uses a Support Vector Machine regressor to fuse multiple elementary metrics into a final quality score, which preserves the strengths of the individual metrics. We evaluate both proposed quality assessment methods on an extended subjective dataset, which we introduce as part of this work. For two of three tested vibrotactile codecs, the MSE between subjective ratings and the SPQI is reduced by 64% and 92%, respectively compared to the state of the art. With our MAF approach, we obtain the only currently available metric that accurately predicts real human user experiments for all three tested codecs. The MAF estimations reduce the average MSE to the subjective ratings over all three tested codecs by 59% compared to the best performing elementary metric.
In this work we compare haptic-based human guidance approaches. We considered both delivering to the user step-by-step instructions towards the goal, and a sensory augmentation policy that provides the knowledge necessary to complete the task using a self-selected strategy. The approaches were evaluated in a collaborative scenario with couples of participants carrying a bulky object under the sole guidance of haptics. Stimuli were generated by a vibrotactile belt according to three haptic policies. Results revealed that the availability of the direction to the destination was a crucial aspect for achieving best temporal performance and high usability ratings.
Model-mediated teleoperation (MMT) is intended to improve system stability and transparency in the presence of time delay between the haptic device and the robot. Previous experimental researches, however, report that systems mediated using linear models become unstable when contacting nonlinear objects. This paper analytically shows the effect of model mismatch on the stability of the system. The analysis shows that the mismatch can generate surplus energy in the haptic system when the stiffness coefficient of the environment increases with the deformed depth. The analysis is verified experimentally in virtual environment with second-order polynomial stiffness object, a linear object with varying stiffness, and a nonlinear viscoelastic object described by Hunt-Crossley model. Results of experiments show that the additionally generated energy destabilizes the system when there is time delay. It is observed that MMT mediated by a linear model becomes unstable even when the object also has linear stiffness if the stiffness changes even once. The experiments with Hunt-Crossley model shows that the damping element may not prevent the instability due to model mismatch.
This work investigates the stability and rendering limitations of admittance-type haptic devices. We investigated a wider range of impedances than had previously been considered, including stiffness, damping, mass, and combinations thereof. The coupled human driving impedance, actuator position control bandwidth, and loop delay are identified as major factors affecting the range of stable impedances. Finally, the theoretical results are experimentally verified using a custom one degree of freedom admittance type haptic device.
By integrating haptic presentation technology and certain haptic sensors into online real-time communication, we can acquire subjective information on others through the sense of touch, and use it as a new standard for our own behavior. We believe that this will lead to changes in people's altruistic behavior, including cooperative behavior. This study investigates behavioral changes during tactile sharing using a behavioral economics scheme. We adopted a sequential public goods game where several participants in a group must exchange money. The haptic condition, where the investment points that other player put can be recognized with vibrotactile sense, and the visual condition, where the investment points that other player put can be visually recognized, were prepared. 32 participants were divided into the visual-first and haptic-first groups, and the haptic or visual condition was alternated between the 1st and 2nd sessions. The results showed significant effects on the haptic experience and correlations with guilty, indicating that the tactile sharing amplified feelings of guilt and made people less likely to act uncooperatively.
The sense of touch can convey semantic and emotional information in social or computer-mediated interactions. Touch plays an essential role in communication with individuals affected by multiple sensory loss, many of whom use modes of touch communication that can be broadly described as tactile sign languages. Few technologies exist today to support such interactions. Here, we present a smart bracelet for facilitating tactile communication and interaction. The smart bracelet captures and analyzes vibrations that are elicited in the skin via touch gestures performed on the hand. We demonstrate the utility of this system for supporting communication via the Deafblind Manual alphabet, which is a tactile sign language. This smart bracelet can classify signed letters with greater than 90 % per-letter accuracy. These results show how existing modes of tactile communication can be integrated with information technologies. This work may furnish new paradigms for human-computer interaction via self- and interpersonal-touch contact.
