Feeling small: exploring the tactile perception limits

Biomechanical Considerations of Refreshable Braille and Tactile Graphics Toward Equitable Access: A Review

This review highlights the biomechanical foundations of braille and tactile graphic discrimination within the context of design innovations in information access for the blind and low-vision community. Braille discrimination is a complex and poorly understood process that necessitates the coordination of motor control, mechanotransduction, and cognitive-linguistic processing. Despite substantial technological advances and multiple design attempts over the last fifty years, a low-cost, high-fidelity refreshable braille and tactile graphics display has yet to be delivered. Consequently, the blind and low-vision communities are left with limited options for information access. This is amplified by the rapid adoption of graphical user interfaces for human-computer interaction, a move that the blind and low vision community were effectively excluded from. Text-to-speech screen readers lack the ability to convey the nuances necessary for science, technology, engineering, arts, and math education and offer limited privacy for the user. Printed braille and tactile graphics are effective modalities but are time and resource-intensive, difficult to access, and lack real-time rendering. Single- and multiline refreshable braille devices either lack functionality or are extremely cost-prohibitive. Early computational models of mechanotransduction through complex digital skin tissue and the kinematics of the braille reading finger are explored as insight into device design specifications. A use-centered, convergence approach for future designs is discussed in which the design space is defined by both the end-user requirements and the available technology.

Recent Advances in Tactile Sensory Systems: Mechanisms, Fabrication, and Applications

Flexible electronics is a cutting-edge field that has paved the way for artificial tactile systems that mimic biological functions of sensing mechanical stimuli. These systems have an immense potential to enhance human-machine interactions (HMIs). However, tactile sensing still faces formidable challenges in delivering precise and nuanced feedback, such as achieving a high sensitivity to emulate human touch, coping with environmental variability, and devising algorithms that can effectively interpret tactile data for meaningful interactions in diverse contexts. In this review, we summarize the recent advances of tactile sensory systems, such as piezoresistive, capacitive, piezoelectric, and triboelectric tactile sensors. We also review the state-of-the-art fabrication techniques for artificial tactile sensors. Next, we focus on the potential applications of HMIs, such as intelligent robotics, wearable devices, prosthetics, and medical healthcare. Finally, we conclude with the challenges and future development trends of tactile sensors.

Effects of Erucamide on Fiber "Softness": Linking Single-Fiber Crystal Structure and Mechanical Properties

Erucamide is known to play a critical role in modifying polymer fiber surface chemistry and morphology. However, its effects on fiber crystallinity and mechanical properties remain to be understood. Here, synchrotron nanofocused X-ray Diffraction (nXRD) revealed a bimodal orientation of the constituent polymer chains aligned along the fiber axis and cross-section, respectively. Erucamide promoted crystallinity in the fiber, leading to larger and more numerous lamellae crystallites. The nXRD nanostructual characterization is complemented by single-fiber uniaxial tensile tests, which showed that erucamide significantly affected fiber mechanical properties, decreasing fiber tensile strength and stiffness but enhancing fiber toughness, fracture strain, and ductility. To correlate these single-fiber nXRD and mechanical test results, we propose that erucamide mediated slip at the interfaces between crystallites and amorphous domains during stress-induced single-fiber crystallization, also decreasing the stress arising from the shear displacement of microfibrils and deformation of the macromolecular network. Linking the single-fiber crystal structure with the single-fiber mechanical properties, these findings provide the direct evidence on a single-fiber level for the role of erucamide in enhancing fiber "softness".

Blinding Is Seeing: A Single-Centre Study Into the Viability of Auto-Injectors for Blinded-Drug Administration in Randomised Controlled Trials

Objective The aim of the study was to assess the viability of auto-injector systems (A-INJ) for preserving investigator blinding in randomized controlled trials (RCT). Background Blinding refers to the concealment of group allocation from one or more individuals involved in a clinical research study. In the dosing of subcutaneous (SC) and intramuscular (IM) investigational medicinal products (IMP), specific challenges arise in maintaining investigator blinding. These challenges primarily involve the active injectate's viscosity and visual appearance (colour/translucency) in comparison to the placebo. Existing methods to control these issues are not perfect. Common approaches include using unblinded investigators or applying films or additives to make the active and placebo injectates appear similar. Method A single-centre experimental and descriptive study was carried out to compare the use of an A-INJ (Owen Mumford, Autoject 2) with the use of a conventional syringe (CS) in delivering a 1 ml dose of both placebo and reference IMP. The percentage delivery of the injectate was compared between the A-INJ IMP and placebo groups. Additionally, eight trained research physicians serving as investigators recorded their assessments of safety and effectiveness after performing serial injections with the A-INJ into a human-tissue analogue. Results Overall, a mean of 95.38% of 1ml placebo injectate was released from the A-INJ, compared to 96.00% from the CS. A total of 94.715% of 1 ml IMP injectate was released from the A-INJ, as opposed to 94.74% from the CS. Independent t-test analyses showed no statistical significance between the experimental arms. The mean administration time was 8.5 seconds. Investigators were unable to differentiate between the two solutions when using the A-INJ. There were no recorded concerns about investigators becoming unblinded, which stands in contrast to concerns associated with using the CS. Conclusion In assessing the viability of A-INJ use in RCTs, we noted a marked improvement when blinding was used. A-INJ systems effectively administer both placebo and active injectates, thereby maintaining the benefit of blinding without the need to alter the placebo through the addition of colourants or viscosity additives. While audio cues from the A-INJ and the time required to administer the injectate pose challenges, solutions are suggested. Although our findings are preliminary, they add to the existing literature on the advantages of A-INJs for administering injectable compounds and offer new perspectives on their utility in RCTs.

A new category of "Aha!" driven by touch: A grip sensation into the directional seam on a baseball

We report an "Aha!" experience which differs from conventional Aha's studied over a century in psychological science. The Aha we introduce is driven by touch instead of the visual and verbal modalities widely studied to date. It can occur when gripping a baseball, with a simple input that the red seam on the ball has a direction. Aided by a symmetry analysis and subsequent survey over literature, we show how our mental and physical representation of a baseball can change suddenly by the seam direction and unravel the factors that make the tactile sense into a joyful-and-insightful sensation. Our study sets a new category of Aha driven by touch, opens a new path to investigate the role of touch in our cognition process, reveals the seam direction as a new degree of freedom in baseball aerodynamics and pitching mechanics, and deepens the insights into throwing a baseball from our fingertips.

Electron Microscopy and Elemental Analysis of Defective Drysdale Nucleus Manipulator Instruments Implicated in Surgical Complications

PURPOSE

To analyze microtopography of 5 reusable Drysdale nucleus manipulator (DNM) paddled tips for sharp defects and evaluate their elemental composition to determine probable source, investigating 2 instruments (DNM 1 and 4) implicated in causing posterior capsule rupture (PCR) and 3 instruments with sharp edges identified by finger-tip interrogation intraoperatively.

DESIGN

Experimental laboratory investigation.

METHODS

DNM paddled tips were analyzed using scanning electron microscopy (SEM) to evaluate for sharp surface defects (number, dimensions), and subsequently energy dispersive x-ray spectroscopy (EDS) performed on sharp defects to determine their elemental composition.

RESULTS

All reused DNMs analyzed (5 of 5) had significant structural defects on SEM analysis including sharp burrs, cavities and indentations, surface debris or residues, and roughening, compared to the new instrument (DNM 3, control) which had no defects. DNM 1 had 2 sharp defects, a larger 14 × 76-µm one and a craterlike 167 × 220-µm defect containing debris. EDS found that DNM 2 had 3 of 4 burrs composed mainly of carbon, the fourth of mixed composition (calcium, sulfur, oxygen); DNM 4 had 1 small burr, EDS significant for carbon; DNM 5 had 3 prominent burrs, the largest of 20 × 28 µm, 2 composed of aluminum, and some carbon residue. DNM 6 had 1 burr composed of aluminum and 3 prominent cavity defects, the largest covering 781 µm².

CONCLUSION

Reusable DNMs are widely used in cataract surgery. Sharp carbon- or aluminum-containing burrs were detected on all reused instruments analyzed together with 1 burr of mixed composition, originating from (1) organic residues, (2) instrument fragments, or (3) salt and contaminant deposits. Sharp defects may contribute to capsular damage including PCR, and residues may pose other safety concerns. Therefore, we support development of a quality, reliable single-use alternative instrument and further encourage careful inspection of all reusable instruments principally by finger-tip interrogation for sharp edges preuse.

Surgical experience and different glove wearing conditions affect tactile sensibility

Background

The fingers' tactile sensibility is essential in surgery, especially in microsurgery. Therefore, surgeons seeking to improve their performance often prefer certain glove brands and wearing habits. There is the need of objectively testing these glove wearing conditions and determine the effect of surgical experience with regard to tactile sensibility by comparing surgeons with non-surgeons.

Methods

This cross-sectional single-center pilot-study was conducted between June and August 2021. Two groups of 27 surgeons and 27 non-surgeons underwent two-point-discrimination (2PD) and Semmes-Weinstein monofilament testing (SWMT) of both index fingers with bare hands and with wearing six different brands of surgical gloves. Different wearing conditions, such as single-gloving, double-gloving, well-fitted, under- and oversized gloves, were evaluated within and between the groups.

Results

Most glove types decreased tactile sensibility (2PD and SWMT) of surgeons and non-surgeons. Interestingly, the thinnest gloves showed similar 2PD values to bare hands in both groups. Double-gloving negatively impacted SWMT, without influencing 2PD. Undersized gloves showed better 2PD and SWMT than well-fitted gloves, while oversized gloves showed no tactile drawbacks. With bare hands and certain glove conditions, the surgeons' 2PD and SWMT was significantly better than the non-surgeons', indicating a positive effect of surgical experience on tactile sensibility.

Conclusion

Our study demonstrated the positive impact of surgical experience on tactile sensibility, as demonstrated by the surgeons. The sensibility of the gloved hand varies on the surgical glove type, but favors thinner gloves, single gloving (rather than double gloving) and undersized or well-fitted gloves.

Perception Accuracy of a Multi-Channel Tactile Feedback System for Assistive Technology

Assistive technology uses multi-modal feedback devices, focusing on the visual, auditory, and haptic modalities. Tactile devices provide additional information via touch sense. Perception accuracy of vibrations depends on the spectral and temporal attributes of the signal, as well as on the body parts they are attached to. The widespread use of AR/VR devices, wearables, and gaming interfaces requires information about the usability of feedback devices. This paper presents results of an experiment using an 8-channel tactile feedback system with vibrators placed on the wrists, arms, ankles, and forehead. Different vibration patterns were designed and presented using sinusoidal frequency bursts on 2, 4, and 8 channels. In total, 27 subjects reported their sensation formally and informally on questionnaires. Results indicate that 2 and 4 channels could be used simultaneously with high accuracy, and the transducers' optimal placement (best sensitivity) is on the wrists, followed by the ankles. Arm and head positions were inferior and generally inadequate for signal presentation. For optimal performance, signal length should exceed 500 ms. Furthermore, the amplitude level and temporal pattern of the presented signals have to be used for carrying information rather than the frequency of the vibration.

The neural basis of tactile texture perception

Running our fingers across a textured surface gives rise to two types of skin deformations, each transduced by different tactile nerve fibers. Coarse features produce large-scale skin deformations whose spatial configuration is reflected in the spatial pattern of activation of some tactile fibers. Scanning a finely textured surface elicits vibrations in the skin, which in turn evoked temporally patterned responses in other fibers. These two neural codes-spatial and temporal-drive a spectrum of neural response properties in somatosensory cortex: At one extreme, neurons are sensitive to spatial patterns and encode coarse features; at the other extreme, neurons are sensitive to vibrations and encode fine features. While the texture responses of nerve fibers are dependent on scanning speed, those of cortical neurons are less so, giving rise to a speed invariant texture percept. Neurons in high-level somatosensory cortices combine information about texture with information about task variables.

Engineering Liquid-Vapor Phase Transition for Refreshable Haptic Interfaces

Haptics as a communication medium has been increasingly emphasized across various disciplines. Recent efforts have focused on developing various haptic stimulation technologies; however, most of them suffer from critical drawbacks stemming from their bulk, complexity, large power input, or high cost. Here, we describe a strategy to design portable and affordable refreshable haptic interfaces composed of an array of individually addressable and controllable liquid pouch motor-based haptic units embedded in either rigid or flexible substrates for different application contexts. The pouch motor filled with low boiling fluid, under a controlled manner, expands or contracts by Joule heating or cooling, enabling the haptic pin in contact to be protruded or retracted. Programming the actuation sequence of an array of haptic units enables the haptic interface to apply different stimuli to the skin to convey corresponding information. We finally demonstrate the applications to portable rigid braille displays and flexible epidermal VR devices. This study opens the avenue to the design of ubiquitous refreshable haptic interfaces that is portable, affordable, scalable, and uninjurious.

Controlling fine touch sensations with polymer tacticity and crystallinity

The friction generated between a finger and an object forms the mechanical stimuli behind fine touch perception. To control friction, and therefore tactile perception, current haptic devices typically rely on physical features like bumps or pins, but chemical and microscale morphology of surfaces could be harnessed to recreate a wider variety of tactile sensations. Here, we sought to develop a new way to create tactile sensations by relying on differences in microstructure as quantified by the degree of crystallinity in polymer films. To isolate crystallinity, we used polystyrene films with the same chemical formula and number averaged molecular weights, but which differed in tacticity and annealing conditions. These films were also sufficiently thin as to be rigid which minimized effects from bulk stiffness and had variations in roughness lower than detectable by humans. To connect crystallinity to human perception, we performed mechanical testing with a mock finger to form predictions about the degree of crystallinity necessary to result in successful discrimination by human subjects. Psychophysical testing verified that humans could discriminate surfaces which differed only in the degree of crystallinity. Although related, human performance was not strongly correlated with a straightforward difference in the degree of crystallinity. Rather, human performance was better explained by quantifying transitions in steady to unsteady sliding and the generation of slow frictional waves (r² = 79.6%). Tuning fine touch with polymer crystallinity may lead to better engineering of existing haptic interfaces or lead to new classes of actuators based on changes in microstructure.

Normal and tangential forces combine to convey contact pressure during dynamic tactile stimulation

Humans need to accurately process the contact forces that arise as they perform everyday haptic interactions such as sliding the fingers along a surface to feel for bumps, sticky regions, or other irregularities. Several different mechanisms are possible for how the forces on the skin could be represented and integrated in such interactions. In this study, we used a force-controlled robotic platform and simultaneous ultrasonic modulation of the finger-surface friction to independently manipulate the normal and tangential forces during passive haptic stimulation by a flat surface. To assess whether the contact pressure on their finger had briefly increased or decreased during individual trials in this broad stimulus set, participants did not rely solely on either the normal force or the tangential force. Instead, they integrated tactile cues induced by both components. Support-vector-machine analysis classified physical trial data with up to 75% accuracy and suggested a linear perceptual mechanism. In addition, the change in the amplitude of the force vector predicted participants' responses better than the change of the coefficient of dynamic friction, suggesting that intensive tactile cues are meaningful in this task. These results provide novel insights about how normal and tangential forces shape the perception of tactile contact.

Artificial SA-I, RA-I and RA-II/vibrotactile afferents for tactile sensing of texture

Robot touch can benefit from how humans perceive tactile textural information, from the stimulation mode to which tactile channels respond, then the tactile cues and encoding. Using a soft biomimetic tactile sensor (the TacTip) based on the physiology of the dermal-epidermal boundary, we construct two biomimetic tactile channels based on slowly adapting SA-I and rapidly adapting RA-I afferents, and introduce an additional sub-modality for vibrotactile information with an embedded microphone interpreted as an artificial RA-II channel. These artificial tactile channels are stimulated dynamically with a set of 13 artificial rigid textures comprising raised-bump patterns on a rotating drum that vary systematically in roughness. Methods employing spatial, spatio-temporal and temporal codes are assessed for texture classification insensitive to stimulation speed. We find: (i) spatially encoded frictional cues provide a salient representation of texture; (ii) a simple transformation of spatial tactile features to model natural afferent responses improves the temporal coding; and (iii) the harmonic structure of induced vibrations provides a pertinent code for speed-invariant texture classification. Just as human touch relies on an interplay between slowly adapting (SA-I), rapidly adapting (RA-I) and vibrotactile (RA-II) channels, this tripartite structure may be needed for future robot applications with human-like dexterity, from prosthetics to materials testing, handling and manipulation.

Data-Driven Playback of Natural Tactile Texture Via Broadband Friction Modulation

We used broadband electroadhesion to reproduce the friction force profile measured as a finger slid across a textured surface. In doing so, we were also able to reproduce with high fidelity the skin vibrations characteristic of that texture; however, we found that this did not reproduce the original perception. To begin, the reproduction felt weak. In order to maximize perceptual similarity between a real texture and its friction force playback, the vibratory magnitude of the latter must be scaled up on average ≈ 3X for fine texture and ≈ 5X for coarse texture samples. This additional gain appears to correlate with perceived texture roughness. Additionally, even with optimal scaling and high fidelity playback, subjects could identify which of two reproductions corresponds to a real texture with only 71 % accuracy, as compared to 95 % accuracy when using real texture alternatives. We conclude that while tribometry and vibrometry data can be useful for texture classification, they appear to contribute only partially to texture perception. We propose that spatially distributed excitation of skin within the fingerpad may play an additional key role, and may thus be able to contribute to high fidelity texture reproduction.

A template-free, more environmentally friendly approach for glass micro-texturing

Micron and nanometer size textured silicate glass surfaces are of interest in consumer electronics, photovoltaics, and biosensing applications. Typically, texturing glass surfaces requires applying a patterned mask or a pre-etching treatment (e.g. sandblasting) on the glass substrate, followed by a mask transferring or etching process using a fluoride-containing compound. The major challenges of such a process are the complexity and cost of masking, and the safety and environmental concerns around the usage and disposal of hydrofluoric acid. Here, we describe a template-free method to construct micron-sized and submicron-sized texture on isotropic glass surfaces in one step. The new texturing mechanisms are well supported by experimental data and peridynamic simulations. With this novel strategy, the etchant uses fluoride-free chemicals such as citric acid to texture silicate glass. Etchant concentration, etch temperature, time, and additives are the primary parameters that dictate the texturing process. Surface feature size and depth can be independently controlled by tuning the leaching and chemical polishing process. We hope this study can trigger more research on novel and more environmentally friendly texturing of isotropic materials.

The neural mechanisms of manual dexterity

The hand endows us with unparalleled precision and versatility in our interactions with objects, from mundane activities such as grasping to extraordinary ones such as virtuoso pianism. The complex anatomy of the human hand combined with expansive and specialized neuronal control circuits allows a wide range of precise manual behaviours. To support these behaviours, an exquisite sensory apparatus, spanning the modalities of touch and proprioception, conveys detailed and timely information about our interactions with objects and about the objects themselves. The study of manual dexterity provides a unique lens into the sensorimotor mechanisms that endow the nervous system with the ability to flexibly generate complex behaviour.

Humans Use a Temporally Local Code for Vibrotactile Perception

Sensory environments are commonly characterized by specific physical features, which sensory systems might exploit using dedicated processing mechanisms. In the tactile sense, one such characteristic feature is frictional movement, which gives rise to short-lasting (<10 ms), information-carrying integument vibrations. Rather than generic integrative encoding (i.e., averaging or spectral analysis capturing the "intensity" and "best frequency"), the tactile system might benefit from, what we call a "temporally local" coding scheme that instantaneously detects and analyzes shapes of these short-lasting features. Here, by employing analytic psychophysical measurements, we tested whether the prerequisite of temporally local coding exists in the human tactile system. We employed pulsatile skin indentations at the fingertip that allowed us to trade manipulation of local pulse shape against changes in global intensity and frequency, achieved by adding pulses of the same shape. We found that manipulation of local pulse shape has strong effects on psychophysical performance, arguing for the notion that humans implement a temporally local coding scheme for perceptual decisions. As we found distinct differences in performance using different kinematic layouts of pulses, we inquired whether temporally local coding is tuned to a unique kinematic variable. This was not the case, since we observed different preferred kinematic variables in different ranges of pulse shapes. Using an established encoding model for primary afferences and indentation stimuli, we were able to demonstrate that the found kinematic preferences in human performance, may well be explained by the response characteristics of Pacinian corpuscles (PCs), a class of human tactile primary afferents.

Neural correlates of tactile hardness intensity perception during active grasping

While tactile sensation plays an essential role in interactions with the surroundings, relatively little is known about the neural processes involved in the perception of tactile information. In particular, it remains unclear how different intensities of tactile hardness are represented in the human brain during object manipulation. This study aims to investigate neural responses to various levels of tactile hardness using functional magnetic resonance imaging while people grasp objects to perceive hardness intensity. We used four items with different hardness levels but otherwise identical in shape and texture. A total of Twenty-five healthy volunteers participated in this study. Before scanning, participants performed a behavioral task in which they received a pair of stimuli and they were to report the perceived difference of hardness between them. During scanning, without any visual information, they were randomly given one of the four objects and asked to grasp it. We found significant blood oxygen-level-dependent (BOLD) responses in the posterior insula in the right hemisphere (rpIns) and the right posterior lobe of the cerebellum (rpCerebellum), which parametrically tracked hardness intensity. These responses were supported by BOLD signal changes in the rpCerebellum and rpIns correlating with tactile hardness intensity. Multidimensional scaling analysis showed similar representations of hardness intensity among physical, perceptual, and neural information. Our findings demonstrate the engagement of the rpCerebellum and rpIns in perceiving tactile hardness intensity during active object manipulation.

Nanotexture Shape and Surface Energy Impact on Electroadhesive Human-Machine Interface Performance

With the ubiquity of touch screens and the commercialization of electroadhesion-based surface haptic devices, modeling tools that capture the multiphysical phenomena within the finger-device interface and their interaction are critical to design devices that achieve higher performance and reliability at lower cost. While electroadhesion has successfully demonstrated the capability to change tactile perception through friction modulation, the mechanism of electroadhesion in the finger-device interface is still unclear, partly due to the complex interfacial physics including contact deformation, capillary formation, electric field, and their complicated coupling effects that have not been addressed comprehensively. A multiphysics model is presented here to predict the friction force for finger-surface tactile interactions at the nanoscale. The nanoscopic multiphysical phenomena are coupled to study the impacts of nanotexture and surface energy in the touch interface. With macroscopic friction force measurements as verification, the model is further used to propose textures that have maximum electroadhesion effect and minimum sensitivity to relative humidity and user perspiration rate. This model can guide the performance improvement of future electroadhesion-based surface haptic devices and other touch-based human-machine interfaces.

Experiencing the Untouchable: A Method for Scientific Exploration and Haptic Fruition of Artworks Microsurface Based on Optical Scanning Profilometry

The experience of an object derives not only from the sight but also from the touch: a tactile exploration can reveal the smallest information trapped within the surface up to our tactile detective threshold. Starting from the importance of this observation in the case of works of art, this research demonstrates the use of conoscopic holography sensors for high-quality acquisition of the surface of artworks (up to the micro-scale) suitable also to 3D printing. The purpose is twofold, allowing for the tactile use of the artwork, which is otherwise impossible, for visually impaired people and for new use in regard to scientific information purposes. In detail, the workflow to obtain a 3D printed replica of multiscale and polychrome artworks suitable for the haptic fruition is validated, but the potential of the tool as an innovative resource for scientific visualization of the microsurface of the artwork for conservation issues is also demonstrated. The validation was performed on notable Italian masterpieces, such as Donatello’s “Death Cristh” bronze relief in Padua and the Tintoretto painting “St. Martial in Glory with the Saints Peter and Paul” in Venice.

The roles of lower- and higher-order surface statistics in tactile texture perception

Humans can haptically discriminate surface textures when there is a significant difference in the statistics of the surface profile. Previous studies on tactile texture discrimination have emphasized the perceptual effects of lower-order statistical features such as carving depth, inter-ridge distance, and anisotropy, which can be characterized by local amplitude spectra or spatial-frequency/orientation subband histograms. However, the real-world surfaces we encounter in everyday life also differ in the higher-order statistics, such as statistics about correlations of nearby spatial-frequencies/orientations. For another modality, vision, the human brain has the ability to use the textural differences in both higher- and lower-order image statistics. In this work, we examined whether the haptic texture perception can use higher-order surface statistics as visual texture perception does, by three-dimensional (3-D)-printing textured surfaces transcribed from different "photos" of natural scenes such as stones and leaves. Even though the maximum carving depth was well above the haptic detection threshold, some texture pairs were hard to discriminate. Specifically, those texture pairs with similar amplitude spectra were difficult to discriminate, which suggests that the lower-order statistics have the dominant effect on tactile texture discrimination. To directly test the poor sensitivity of the tactile texture perception to higher-order surface statistics, we matched the lower-order statistics across different textures using a texture synthesis algorithm and found that haptic discrimination of the matched textures was nearly impossible unless the stimuli contained salient local features. We found no evidence for the ability of the human tactile system to use higher-order surface statistics for texture discrimination.NEW & NOTEWORTHY Humans can discriminate subtle spatial patterns differences in the surrounding world through their hands, but the underlying computation remains poorly understood. Here, we 3-D-printed textured surfaces and analyzed the tactile discrimination performance regarding the sensitivity to surface statistics. The results suggest that observers have sensitivity to lower-order statistics whereas not to higher-order statistics. That is, touch differs from vision not only in spatiotemporal resolution but also in (in)sensitivity to high-level surface statistics.

Predicting human touch sensitivity to single atom substitutions in surface monolayers for molecular control in tactile interfaces

The mechanical stimuli generated as a finger interrogates the physical and chemical features of an object form the basis of fine touch. Haptic devices, which are used to control touch, primarily focus on recreating physical features, but the chemical aspects of fine touch may be harnessed to create richer tactile interfaces and reveal fundamental aspects of tactile perception. To connect tactile perception with molecular structure, we systematically varied silane-derived monolayers deposited onto surfaces smoother than the limits of human perception. Through mechanical friction testing and cross-correlation analysis, we made predictions of which pairs of silanes might be distinguishable by humans. We predicted, and demonstrated, that humans can distinguish between two isosteric silanes which differ only by a single nitrogen-for-carbon substitution. The mechanism of tactile contrast originates from a difference in monolayer ordering, as quantified by the Hurst exponent, which was replicated in two alkylsilanes with a three-carbon difference in length. This approach may be generalizable to other materials and lead to new tactile sensations derived from materials chemistry.

The Immediate Effect of Informational Manual Therapy for Improving Quiet Standing and Bodily Pain in University Population

Background: The Informational Manual Therapy (IMT) is a therapeutic touch. This study aims to assess the effect of IMT on quiet standing, pain and health status in university population. Methods: An experiment was conducted on subjects utilizing a comparative paired analysis both before and after the intervention. One IMT session was performed on 57 healthy individuals aged from 18 to 65 years. The primary outcome was quiet standing assessed by the Satel 40 Hz stabilometric force platform. Secondary outcomes were bodily pain assessed by the 36-Item Short Form Survey (SF-36) and health status by EQ-5D-3L. The primary outcome was evaluated before and immediately after treatment. Results: The individuals were divided into 3 age groups, 18–35 (52.6%), 35–50 (29.8%) and 51–65 (17.6%). Statistically significant differences were immediately observed after the session ended when comparing the pre-post quiet stance scores in a number of length parameters: L, Lx, Ly and stabilometry amplitude on Y-axis with eyes open and closed. Significant differences were also found when testing bodily pain (SF-36) and anxiety (5Q-5D-3L). Conclusion: One session of IMT produced positive effects when testing quiet standing with eyes open and eyes closed, as well as a significant reduction in pain and anxiety for those tested. Further research is suggested.

The neonatal assessment manual score (NAME) for improving the clinical management of infants: a perspective validity study

BACKGROUND AND OBJECTIVES

The Neonatal Assessment Manual scorE (NAME) was developed to assist in the clinical management of infants in the neonatal ward by assessing their body's compliance and homogeneity. The present study begins its validation process.

METHODS

An expert panel of neonatal intensive care unit (NICU) professionals investigated the NAME face and content validity. Content validity was assessed through the content validity index (CVI). Construct validity was assessed using data collected from 50 newborns hospitalized in the NICU of "Vittore Buzzi" Children Hospital of Milan, Italy. Kendall's τ and ordinal logistic regressions were used to evaluate the correlation between the NAME scores and infants' gestational age, birth weight, post-menstrual age, weight at the time of assessment, and a complexity index related to organic complications.

RESULTS

The CVIs for compliance, homogeneity, and the whole scale were respectively 1, 0.9, and 0.95. Construct validity analysis showed significant positive correlations between the NAME and infants' weight and age, and a negative correlation between the NAME and the complexity index (τ = - 0.31 [95% IC: - 0.47, - 0.12], p = 0.016 and OR = 0.56 [95% IC: 0.32, 0.94], p = 0.034 for categorical NAME; τ = - 0.32 [95% IC: - 0.48, - 0.14], p = 0.005 for numerical NAME).

CONCLUSIONS

The NAME was well accepted by NICU professionals in this study and it demonstrates good construct validity in discriminating the infant's general condition. Future studies are needed to test the NAME reliability and predictive capacity.

Tactile active sensing in an insect plant pollinator

The interaction between insects and the flowers they pollinate has driven the evolutionary diversity of both insects and flowering plants, two groups with the most numerous species on Earth. Insects use vision and olfaction to localize host plants, but we know relatively little about how they find the tiny nectary opening in the flower, which can be well beyond their visual resolution. Especially when vision is limited, touch becomes crucial in successful insect-plant pollination interactions. Here, we studied the remarkable feeding behavior of crepuscular hawkmoths Manduca sexta, which use their long, actively controlled, proboscis to expertly explore flower-like surfaces. Using machine vision and 3D-printed artificial flower-like feeders, we revealed a novel behavior that shows moths actively probe surfaces, sweeping their proboscis from the feeder edge to its center repeatedly until they locate the nectary opening. Moreover, naive moths rapidly learn to exploit these flowers, and they adopt a tactile search strategy to more directly locate the nectary opening in as few as three to five consecutive visits. Our results highlight the proboscis as a unique active sensory structure and emphasize the central role of touch in nectar foraging insect-plant pollinator interactions.

A review of the neurobiomechanical processes underlying secure gripping in object manipulation

O'SHEA, H. and S. J. Redmond. A review of the neurobiomechanical processes underlying secure gripping in object manipulation. NEUROSCI BIOBEHAV REV 286-300, 2021. Humans display skilful control over the objects they manipulate, so much so that biomimetic systems have yet to emulate this remarkable behaviour. Two key control processes are assumed to facilitate such dexterity: predictive cognitive-motor processes that guide manipulation procedures by anticipating action outcomes; and reactive sensorimotor processes that provide important error-based information for movement adaptation. Notwithstanding increased interdisciplinary research interest in object manipulation behaviour, the complexity of the perceptual-sensorimotor-cognitive processes involved and the theoretical divide regarding the fundamentality of control mean that the essential mechanisms underlying manipulative action remain undetermined. In this paper, following a detailed discussion of the theoretical and empirical bases for understanding human dexterous movement, we emphasise the role of tactile-related sensory events in secure object handling, and consider the contribution of certain biophysical and biomechanical phenomena. We aim to provide an integrated account of the current state-of-art in skilled human-object interaction that bridges the literature in neuroscience, cognitive psychology, and biophysics. We also propose novel directions for future research exploration in this area.

Finger Pad Topography beyond Fingerprints: Understanding the Heterogeneity Effect of Finger Topography for Human-Machine Interface Modeling

With the rapid development of haptic devices, there is an increasing demand to understand finger pad topography under different conditions, especially for investigation of the human-machine interface in surface haptic devices. An accurate description of finger pad topography across scales is essential for the study of the interfaces and could be used to predict the real area of contact and friction force, both of which correlate closely with human tactile perception. However, there has been limited work reporting the heterogeneous topography of finger pads across scales. In this work, we propose a detailed heterogeneous finger topography model based on the surface roughness power spectrum. The analysis showed a significant difference between the topography on ridges and valleys of the fingerprint and that the real contact area estimation could be different by a factor of 3. In addition, a spatial-spectral analysis method is developed to effectively compare topography response to different condition changes. This paper provides insights into finger topography for advanced human-machine interaction interfaces.

Fingerprint ridges allow primates to regulate grip

Fingerprints are unique to primates and koalas but what advantages do these features of our hands and feet provide us compared with the smooth pads of carnivorans, e.g., feline or ursine species? It has been argued that the epidermal ridges on finger pads decrease friction when in contact with smooth surfaces, promote interlocking with rough surfaces, channel excess water, prevent blistering, and enhance tactile sensitivity. Here, we found that they were at the origin of a moisture-regulating mechanism, which ensures an optimal hydration of the keratin layer of the skin for maximizing the friction and reducing the probability of catastrophic slip due to the hydrodynamic formation of a fluid layer. When in contact with impermeable surfaces, the occlusion of the sweat from the pores in the ridges promotes plasticization of the skin, dramatically increasing friction. Occlusion and external moisture could cause an excess of water that would defeat the natural hydration balance. However, we have demonstrated using femtosecond laser-based polarization-tunable terahertz wave spectroscopic imaging and infrared optical coherence tomography that the moisture regulation may be explained by a combination of a microfluidic capillary evaporation mechanism and a sweat pore blocking mechanism. This results in maintaining an optimal amount of moisture in the furrows that maximizes the friction irrespective of whether a finger pad is initially wet or dry. Thus, abundant low-flow sweat glands and epidermal furrows have provided primates with the evolutionary advantage in dry and wet conditions of manipulative and locomotive abilities not available to other animals.

Physical limits to sensing material properties

All materials respond heterogeneously at small scales, which limits what a sensor can learn. Although previous studies have characterized measurement noise arising from thermal fluctuations, the limits imposed by structural heterogeneity have remained unclear. In this paper, we find that the least fractional uncertainty with which a sensor can determine a material constant λ0 of an elastic medium is approximately [Formula: see text] for a ≫ d ≫ ξ, [Formula: see text], and D > 1, where a is the size of the sensor, d is its spatial resolution, ξ is the correlation length of fluctuations in λ0, Δλ is the local variability of λ0, and D is the dimension of the medium. Our results reveal how one can construct devices capable of sensing near these limits, e.g. for medical diagnostics. We use our theoretical framework to estimate the limits of mechanosensing in a biopolymer network, a sensory process involved in cellular behavior, medical diagnostics, and material fabrication.

Tactile perception of randomly rough surfaces

Most everyday surfaces are randomly rough and self-similar on sufficiently small scales. We investigated the tactile perception of randomly rough surfaces using 3D-printed samples, where the topographic structure and the statistical properties of scale-dependent roughness were varied independently. We found that the tactile perception of similarity between surfaces was dominated by the statistical micro-scale roughness rather than by their topographic resemblance. Participants were able to notice differences in the Hurst roughness exponent of 0.2, or a difference in surface curvature of 0.8 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {mm}^{-1}$$\end{document}mm-1 for surfaces with curvatures between 1 and 3 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {mm}^{-1}$$\end{document}mm-1. In contrast, visual perception of similarity between color-coded images of the surface height was dominated by their topographic resemblance. We conclude that vibration cues from roughness at the length scale of the finger ridge distance distract the participants from including the topography into the judgement of similarity. The interaction between surface asperities and fingertip skin led to higher friction for higher micro-scale roughness. Individual friction data allowed us to construct a psychometric curve which relates similarity decisions to differences in friction. Participants noticed differences in the friction coefficient as small as 0.035 for samples with friction coefficients between 0.34 and 0.45.

The Cranial Bowl in the New Millennium and Sutherland's Legacy for Osteopathic Medicine: Part 2

Cranial osteopathic medicine is practiced all over the world, respecting the dictates of the creator, Dr Sutherland. Despite the current manual approach faithfully follows the theoretical and practical bases that make up the cranial model of the last century, there are many scientific evidences that highlight the criticalities of the same model. In the first part we reviewed the role of the meninges and cerebrospinal fluid (CSF), as well as we discussed some rhythms present in the central nervous system; these latter elements are the pillars to support the theoretical idea of the movement of the skull evaluated and palpated by the osteopath. In this second part we will review the mechanical characteristics of other structures that make up the cranial system, highlighting new perspectives for clinical practice, thanks to the most recent data derived from scientific research.

Organic Haptics: Intersection of Materials Chemistry and Tactile Perception

The goal of the field of haptics is to create technologies that manipulate the sense of touch. In virtual and augmented reality, haptic devices are for touch what loudspeakers and RGB displays are for hearing and vision. Haptic systems that utilize micromotors or other miniaturized mechanical devices (e.g., for vibration and pneumatic actuation) produce interesting effects, but are quite far from reproducing the feeling of real materials. They are especially deficient in recapitulating surface properties: fine texture, friction, viscoelasticity, tack, and softness. The central argument of this Progress Report is that to reproduce the feel of everyday objects requires chemistry: molecular control over the properties of materials and ultimately design of materials which can change these properties in real time. Stimuli-responsive organic materials, such as polymers and composites, are a class of materials which can change their oxidation state, conductivity, shape, and rheological properties, and thus might be useful in future haptic technologies. Moreover, the use of such materials in research on tactile perception could help elucidate the limits of human tactile sensitivity. The work described represents the beginnings of this new area of inquiry, in which the defining approach is the marriage of materials science and psychology.

The finishing touches: the role of friction and roughness in haptic perception of surface coatings

Humans are extraordinarily skilled in the tactile evaluation of, and differentiation between, surfaces. The chemical and mechanical properties of these surfaces are translated into tactile signals during haptic exploration by mechanoreceptors in our skin, which are specialized to respond to different types of temporal and mechanical stimulation. Describing the effects of measurable physical characteristics on the human response to tactile exploration of surfaces is of great interest to manufacturers of household materials so that the haptic experience can be considered during design, product development and quality control. In this study, methods from psychophysics and materials science are combined to advance current understanding of which physical properties affect tactile perception of a range of furniture surfaces, i.e., foils and coatings, thus creating a tactile map of the furniture product landscape. Participants’ responses in a similarity scaling task were analyzed using INDSCAL from which three haptic dimensions were identified. Results show that specific roughness parameters, tactile friction and vibrational information, as characterized by a stylus profilometer, a Forceboard, and a biomimetic synthetic finger, are important for tactile differentiation and preferences of these surface treatments. The obtained dimensions are described as distinct combinations of the surface properties characterized, rather than as ‘roughness’ or ‘friction’ independently. Preferences by touch were related to the roughness, friction and thermal properties of the surfaces. The results both complement and advance current understanding of how roughness and friction relate to tactile perception of surfaces.

Virtual Texture Generated using Elastomeric Conductive Block Copolymer in Wireless Multimodal Haptic Glove

Haptic devices are in general more adept at mimicking the bulk properties of materials than they are at mimicking the surface properties. This paper describes a haptic glove capable of producing sensations reminiscent of three types of near-surface properties: hardness, temperature, and roughness. To accomplish this mixed mode of stimulation, three types of haptic actuators were combined: vibrotactile motors, thermoelectric devices, and electrotactile electrodes made from a stretchable conductive polymer synthesized in our laboratory. This polymer consisted of a stretchable polyanion which served as a scaffold for the polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT). The scaffold was synthesized using controlled radical polymerization to afford material of low dispersity, relatively high conductivity (0.1 S cm-1), and low impedance relative to metals. The glove was equipped with flex sensors to make it possible to control a robotic hand and a hand in virtual reality (VR). In psychophysical experiments, human participants were able to discern combinations of electrotactile, vibrotactile, and thermal stimulation in VR. Participants trained to associate these sensations with roughness, hardness, and temperature had an overall accuracy of 98%, while untrained participants had an accuracy of 85%. Sensations could similarly be conveyed using a robotic hand equipped with sensors for pressure and temperature.

The Rhythmic Finger Focus Hypnotic Technique: Multilevel Application of Ericksonian Utilization

This paper presents a hypnotic technique that starts with a suggested focus on one's fingertips, and movement of the hands in a self-determined rhythm. The technique involves the use of the utilization principle of Milton Erickson in multiple ways. This includes utilizing psychomotor agitation characteristic of psychophysiological arousal, directing it toward movement that generates the sensations upon which to focus. It utilizes the sensitivity of the fingertips, the high degree of representation of the hands in the somatosensory cortex, and the tendency of the brain to orient to novelty to help facilitate focused absorption. It generates counter stimulation for pain management, and emotionally self- soothing tactile sensations. The technique is further designed to activate and utilize prior sensorimotor learning and sensory experiences associated with the hands to access feelings of mastery, creativity, flow, self-efficacy, and other positive emotional experiences. It is hypothesized that multisystem coherence is generated through activating prior positive motor, behavioral and affective experiential learning. It is further hypothesized that the rhythmic movement and sensory input simultaneously generated by and processed in the right and left hemispheres, entrains the hemispheres toward greater sympathetic/parasympathetic balance.

Multiscale characterisation of single synthetic fibres: Surface morphology and nanomechanical properties

HYPOTHESIS

Thermal through-air bonding process and slip additive treatment affect fibre surface structure and nanomechanical properties, which is extremely difficult to characterise on a single-fibre level.

EXPERIMENTS

Optical microscopy (OM) was applied to study the effect of air-through bonding, spunbonding, and crimping on fibre geometry and general appearance. A "spray-on" method developed here using a custom-designed fibre holder allowed a direct measurement of static contact angles of water droplets on single fibres. Scanning electron microscopy (SEM) showed different morphological features on the fibre due to the nonwoven fabric-making process and additive treatment. Synchrotron X-ray diffraction (XRD) was applied to study the effect of erucamide presence on polypropylene (PP) fibre crystal structure. Atomic force microscopy (AFM) imaging provided complementary characterization of fibre topographic features such as average surface roughness, along with adhesion force mapping by quantitative nanomechanical (QNM) AFM imaging.

FINDINGS

Our results show the effect of nonwoven making process and surfactant additive treatment on the fibre surface structure and nanomechanical properties. Wettability experiment on the single fibre revealed the hydrophobic nature of all the synthetic fibres. For polyethylene/polyethylene terephthalate (PE/PET) bicomponent single fibres, the polyethylene sheath was found to possess fibrillar microstructure - typical for drawn fibres, whereas the fibres entangled in nonwoven fabrics exhibited a uniform, porous surface morphology attributed to the through-air process. Adhesion force mapping allowed us to correlate fibre nanomechanical properties with its topography, with surface pore interiors showing higher adhesion than the flat polyethylene region. Furthermore, on the polypropylene (PP) fibre surface treated with erucamide (13-cis-docosenamide; a common slip additive used in polyolefin film processing), we observed overlapping multilayers consisting of 4 nm erucamide bilayers, attributed to the slip additive migration onto the fibre surface. XRD measurements of the fibres did not detect the presence of erucamide; however, AFM imaging provided evidence for its migration to the fibre surface, imparting influence on the surface structure and adhesive properties of the fibre. Single-fibre AFM imaging also allowed a detailed analysis of different surface roughness parameters, revealing that both through-air bonding in the nonwoven making process and the slip additive (erucamide) treatment affected the fibre surface roughness. The wettability, surface morphology, and adhesion properties from this study, obtained with unprecedented resolution and details on single fibres, are valuable to informing rational design of fibre processing for fibre optimal properties, critically important in many industrial applications.

Coding source localization through inter-spike delay: modelling a cluster of Pacinian Corpuscles using time-division multiplexing approach

The Pacinian Corpuscle (PC) is the most sensitive mechanoreceptor in the human body found in clusters of two or three. We extended our previous model of an isolated-PC to a cluster-PC focussing on relative spike delay and displacement threshold for understanding how the stimulus location is coded. In our model, two PCs with Gaussian overlapping receptive fields are arranged beneath the skin model. For a spatiotemporal stimulus (vibration), the model response is proposed to be a time-division multiplexing of responses from two PCs within the cluster. While the spike rate characteristics and pole-zero plot of cluster-PC model show similarities with the isolated-PC model, the frequency response shows ripples after 1 kHz as the distance (d) between the PCs increases. The stimulus location [Formula: see text] and d influence the relative spike delay and the displacement threshold, but not the spike rate. The novel contributions from our model include prediction of (i) relative spike delay for various d, stimulus frequency (f), and ψ, (ii) spike rate characteristics for varying f, and (iii) displacement threshold curve as a function of frequency for various d. Although the physiological validation of the novel predictions is impractical, we have validated the relative spike delay and the displacement threshold curves with experimental data in the literature.

Evolution of epimorphosis in mammals

Mammalian epimorphic regeneration is rare and digit tip regeneration in mice is the best-studied model for a multi-tissue regenerative event that involves blastema formation. Digit tip regeneration parallels human fingertip regeneration, thus understanding the details of this response can provide insight into developing strategies to expand the potential of human regeneration. Following amputation, the digit stump undergoes a strong histolytic response involving osteoclast-mediated bone degradation that is spatially and temporally linked to the expansion of blastema osteoprogenitor cells. Blastemal differentiation occurs via direct intramembranous ossification. Although robust, digit regeneration is imperfect: The amputated cortical bone is replaced with woven bone and there is excessive bone regeneration restricted to the dorsal-ventral axis. Ontogenetic and phylogenetic analysis of digit regeneration in amphibians and mammals raise the possibility that mammalian blastema is a product of convergent evolution and we hypothesize that digit tip regeneration evolved from a nonregenerative precondition. A model is proposed in which the mammalian blastema evolved in part from an adaptation of two bone repair strategies (the bone remodeling cycle and fracture healing) both of which are conserved across tetrapod vertebrates. The view that epimorphic regeneration evolved in mammals from a nonregenerative precondition is supported by recent studies demonstrating that complex regenerative responses can be induced from a number of different nonregenerative amputation wounds by specific modification of the healing response.

Neonatal Assessment Manual Score: Is There a Role of a Novel, Structured Touch-Based Evaluation in Neonatal Intensive Care Unit?

Despite the technological improvements in monitoring preterm infants in the neonatal intensive care unit, routine care in the neonatal ward is primarily based on manual procedures. Although manual clinical procedures play a critical role in neonatology, little attention has been paid to palpation as a clinical assessment tool. Palpation is a clinical evaluation tool that relies mostly on the senses of touch and proprioception. Based on recent studies investigating the role and clinical effectiveness of touch in full-term and preterm babies, this paper proposes an evaluative touch-based procedure-the Neonatal Assessment Manual Score (NAME) model-that could be useful in the neonatal ward and describes its rationale. The operator applies gentle light pressures to the infant's body. In essence, the touch stimulates low-threshold afferent fibers that could influence the interoceptive cerebral network and the autonomic nervous system, thus altering the blood flow and breathing rhythm. These events could change how bodily fluids distribute among body segments and hence the body volume. The volume modification could be felt manually through haptic perception owing to the high sensitivity of the fingers. On the basis of their clinical conditions and stage of development, infants will respond differently to the applied pressures. Evaluating the infant's response, the operator produces a score of "bad," "marginal," or "good" for communicating quickly and clearly the infant's conditions to other professionals. Because the NAME model is intended for every professional who is used to touch-based procedures, if future studies confirmed its validity and reliability in clinical practice, the NAME model could become a part of the neonatal ward routine care for better assessing and managing the infant's conditions, even during emergencies.

Emergence of an Invariant Representation of Texture in Primate Somatosensory Cortex

A major function of sensory processing is to achieve neural representations of objects that are stable across changes in context and perspective. Small changes in exploratory behavior can lead to large changes in signals at the sensory periphery, thus resulting in ambiguous neural representations of objects. Overcoming this ambiguity is a hallmark of human object recognition across sensory modalities. Here, we investigate how the perception of tactile texture remains stable across exploratory movements of the hand, including changes in scanning speed, despite the concomitant changes in afferent responses. To this end, we scanned a wide range of everyday textures across the fingertips of rhesus macaques at multiple speeds and recorded the responses evoked in tactile nerve fibers and somatosensory cortical neurons (from Brodmann areas 3b, 1, and 2). We found that individual cortical neurons exhibit a wider range of speed-sensitivities than do nerve fibers. The resulting representations of speed and texture in cortex are more independent than are their counterparts in the nerve and account for speed-invariant perception of texture. We demonstrate that this separation of speed and texture information is a natural consequence of previously described cortical computations.

Audio-Tactile Skinny Buttons for Touch User Interfaces

This study proposes a novel skinny button with multimodal audio and haptic feedback to enhance the touch user interface of electronic devices. The active material in the film-type actuator is relaxor ferroelectric polymer (RFP) poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)] blended with poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)], which produces mechanical vibrations via the fretting vibration phenomenon. Normal pressure applied by a human fingertip on the film-type skinny button mechanically activates the locally concentrated electric field under the contact area, thereby producing a large electrostrictive strain in the blended RFP film. Multimodal audio and haptic feedback is obtained by simultaneously applying various electric signals to the pairs of ribbon-shaped top and bottom electrodes. The fretting vibration provides tactile feedback at frequencies of 50–300 Hz and audible sounds at higher frequencies of 500 Hz to 1 kHz through a simple on-off mechanism. The advantage of the proposed audio-tactile skinny button is that it restores the “click” sensation to the popular virtual touch buttons employed in contemporary electronic devices.

Role of indentation depth and contact area on human perception of softness for haptic interfaces

In engineering, the "softness" of an object, as measured by an indenter, manifests as two measurable parameters: (i) indentation depth and (ii) contact area. For humans, softness is not well defined, although it is believed that perception depends on the same two parameters. Decoupling their relative contributions, however, has not been straightforward because most bulk-"off-the-shelf"-materials exhibit the same ratio between the indentation depth and contact area. Here, we decoupled indentation depth and contact area by fabricating elastomeric slabs with precise thicknesses and microstructured surfaces. Human subject experiments using two-alternative forced-choice and magnitude estimation tests showed that the indentation depth and contact area contributed independently to perceived softness. We found an explicit relationship between the perceived softness of an object and its geometric properties. Using this approach, it is possible to design objects for human interaction with a desired level of perceived softness.

Electronic Skin to Feel "Pain": Detecting "Prick" and "Hot" Pain Sensations

An artificial tactile system has attracted tremendous interest and intensive study, since it can be applied as a new functional interface between humans and electronic devices. Unfortunately, most previous works focused on improving the sensitivity of sensors. However, humans also respond to psychological feelings for sensations such as pain, softness, or roughness, which are important factors for interacting with others and objects. Here, we present an electronic skin concept that generates a "pain" warning signal, specifically, to sharp "prick" and "hot" sensations. To simplify the sensor structure for these two feelings, a single-body tactile sensor design is proposed. By exploiting "hot" feeling based on the Seebeck effect instead of the pyroelectric property, it is possible to distinguish points registering a "hot" feeling from those generating a "prick" feeling, which is based on the piezoelectric effect. The control of free carrier concentration in nanowire induced the appropriate level of Seebeck current, which enabled the sensor system to be more reliable. The first derivatives of the piezo and Seebeck output signals are the key factors for the signal processing of the "pain" feeling. The main idea can be applied to mimic other psychological tactile feelings.

Oral somatosensatory acuity is related to particle size perception in chocolate

Texture affects liking or rejection of many foods for clinically relevant populations and the general public. Phenotypic differences in chemosensation are well documented and influence food choices, but oral touch perception is less understood. Here, we used chocolate as a model food to explore texture perception, specifically grittiness perception. In Experiment 1, the Just Noticeable Difference (JND) for particle size in melted chocolate was ~5 μm in a particle size range commonly found in commercial chocolates; as expected, the JND increased with particle size, with a Weber Fraction of ~0.17. In Experiment 2, individual differences in touch perception were explored: detection and discrimination thresholds for oral point pressure were determined with Von Frey Hairs. Discrimination thresholds varied across individuals, allowing us to separate participants into high and low sensitivity groups. Across all participants, two solid commercial chocolates (with particle sizes of 19 and 26 μm; i.e., just above the JND) were successfully discriminated in a forced-choice task. However, this was driven entirely by individuals with better oral acuity: 17 of 20 of more acute individuals correctly identified the grittier chocolate versus 12 of 24 less acute individuals. This suggests phenotypic differences in oral somatosensation can influence texture perception of foods.

Healable Thermoplastic for Kinesthetic Feedback in Wearable Haptic Devices

The word "haptics" refers to technologies designed to stimulate the tactile and kinesthetic senses. Kinesthesia-the sense of motion-is triggered by imposing forces upon the joints, tendons, and muscles to recreate the geometry and stiffness of objects, as may be useful in physical therapy or virtual reality. Here, we introduce a form of kinesthetic feedback by manipulating the mechanical properties of spandex impregnated with a thermoplastic polymer. Heating or cooling this textile-thermoplastic composite just above or below its glass transition temperature (T g) dramatically changes its mechanical properties (corresponding to a decrease in storage modulus from 36 MPa to 0.55 MPa). In the form of a glove, the composite can also be healed after inadvertent overextension in its stiffened state by heating it above its T g. When fitted with thermoelectric devices for active heating and cooling, the flexible or stiffened state of a glove can be perceived by human subjects. As an example of a human-machine interface, the glove is used to control a robotic finger. When the robotic finger makes contact with a wall, a signal is sent to thermoelectric devices in the glove to cool (stiffen the finger) and thus provide kinesthetic feedback to the user.

High-dimensional representation of texture in somatosensory cortex of primates

The sense of touch affords a remarkable sensitivity to the microstructure of surfaces, affording us the ability to sense elements ranging in size from tens of nanometers to tens of millimeters. The hand sends signals about texture to the brain using three classes of nerve fibers through two neural codes: coarse features in spatial patterns of activation and fine features in precise temporal spiking patterns. In this study, we show that these nerve signals culminate in a complex, high-dimensional representation of texture in somatosensory cortex, whose structure can account for the structure of texture perception. This complexity arises from the neurons that act as idiosyncratic detectors of spatial and/or temporal motifs in the afferent input.

In the somatosensory nerves, the tactile perception of texture is driven by spatial and temporal patterns of activation distributed across three populations of afferents. These disparate streams of information must then be integrated centrally to achieve a unified percept of texture. To investigate the representation of texture in somatosensory cortex, we scanned a wide range of natural textures across the fingertips of rhesus macaques and recorded the responses evoked in Brodmann’s areas 3b, 1, and 2. We found that texture identity is reliably encoded in the idiosyncratic responses of populations of cortical neurons, giving rise to a high-dimensional representation of texture. Cortical neurons fall along a continuum in their sensitivity to fine vs. coarse texture, and neurons at the extrema of this continuum seem to receive their major input from different afferent populations. Finally, we show that cortical responses can account for several aspects of texture perception in humans.