Biomimetic Electronic Skin for Robots Aiming at Superior Dynamic-Static Perception and Material Cognition Based on Triboelectric-Piezoresistive Effects.

Empowering robots with tactile perception and even thinking as well as judgment capabilities similar to those of humans is an inevitable path for the development of future robots. Here, we propose a biomimetic electronic skin (BES) that truly serves and applies to robots to achieve superior dynamic-static perception and material cognition functionalities. First, the microstructured triboelectric and piezoresistive layers are fabricated by a facile template method followed by selected self-polymerization treatment, enabling BES with high sensitivity and a wide detection range. Further, through laminated-independent triboelectric and piezoresistive parts for perceiving dynamic and static pressures simultaneously, the BES is capable of supporting the robot hand to monitor the entire process during object grasping. Most importantly, by further combining a neural network model, an intelligent cognition system is constructed for real-time cognition of the object material species via one touch of the robot hand under arbitrary pressures, which goes beyond the human cognition ability.

Color-Shifting Iontronic Skin for On-Site, Nonpixelated Pressure Mapping Visualization.

Mimicking the function of human skin is highly desired for electronic skins (e-skins) to perceive the tactile stimuli by both their intensity and spatial location. The common strategy using pixelated pressure sensor arrays and display panels greatly increases the device complexity and compromises the portability of e-skins. Herein, we tackled this challenge by developing a user-interactive iontronic skin that simultaneously achieves electrical pressure sensing and on-site, nonpixelated pressure mapping visualization. By merging the electrochromic and iontronic pressure sensing units into an integrated multilayer device, the interlayer charge transfer is regulated by applied pressure, which induces both color shifting and a capacitance change. The iontronic skin could visualize the trajectory of dynamic forces and reveal both the intensity and spatial information on various human activities. The integration of dual-mode pressure responsivity, together with the scalable fabrication and explicit signal output, makes the iontronic skin highly promising in biosignal monitoring and human-machine interaction.

Biomimetic Ion Channel Regulation for Temperature-Pressure Decoupled Tactile Perception.

The perception of temperature and pressure of skin plays a vital role in joint movement, hand grasp, emotional expression, and self-protection of human. Among many biomimetic materials, ionic gels are uniquely suited to simulate the function of skin due to its ionic transport mechanism. However, both the temperature and pressure sensing are heavily dependent on the changes in ionic conductivity, making it impossible to decouple the temperature and pressure signals. Here, a pressure-insensitive and temperature-modulated ion channel is designed by synergistic strategies for gel skeleton's compact packing and ultra-thin structure, mimicking the function of the temperature ion channel in human skin. This ion-confined gel can completely suppress the pressure response of the temperature sensing layer. Furthermore, a temperature-pressure decoupled ionic sensor is fabricated and it is demonstrated that the ionic sensor can sense complex signals of temperature and pressure. This novel and effective approach has great potential to overcome one of the current barriers in developing ionic skin and extending its applications.

Contribution of external reference frame to tactile localization.

The purpose of the present study was to elucidate whether an external reference frame contributes to tactile localization in blindfolded healthy humans. In a session, the right forearm was passively moved until the elbow finally reached to the target angle, and participants reached the left index finger to the right middle fingertip. The locus of the right middle fingertip indicated by the participants deviated in the direction of the elbow extension when vibration was provided to the biceps brachii muscle during the passive movement. This finding indicates that proprioception contributes to the identification of the spatial coordinate of the specific body part in an external reference frame. In another session, the tactile stimulus was provided to the dorsal of the right hand during the passive movement, and the participants reached the left index finger to the spatial locus at which the tactile stimulus was provided. Vibration to the biceps brachii muscle did not change the perceived locus of the tactile stimulus indicated by the left index finger. This finding indicates that an external reference frame does not contribute to tactile localization during the passive movement. Humans may estimate the spatial coordinate of the tactile stimulus based on the time between the movement onset and the time at which the tactile stimulus is provided.

Is it really on your hand? Spontaneous sensations are not peripheral sensations - Evidence from able-bodied individuals and a phantom limb syndrome patient.

Among other bodily signals, the perception of sensations arising spontaneously on the skin with no external triggers contributes to body awareness. The topic of spontaneous sensations (SPS) being quite recent in the literature, there is still a debate whether this phenomenon is elicited by peripheral cutaneous units' activity underlying tactile perception or originates directly from central mechanisms. In a first experiment, we figured that, if SPS depended on peripheral afferents, their perception on the glabrous hand should relate to the hand tactile sensitivity. On the contrary, we found no relationship at all, which led us to envisage the scenario of SPS in the absence of cutaneous units. In a second experiment, we present the case of Julie, a right-hand amputee that could perceive and report SPS arising on her phantom limb syndrome. We found that SPS distribution on the phantom limb followed the same gradient as that observed in control participants, unlike SPS perceived on the intact left hand. Those findings are crucial to the understanding of neural factors determining body awareness through SPS perception and provide insights into the existence of a precise neural gradient underlying somesthesis.

Crossmodal associations between naturally occurring tactile and sound textures.

This study investigates the crossmodal associations between naturally occurring sound textures and tactile textures. Previous research has demonstrated the association between low-level sensory features of sound and touch, as well as higher-level, cognitively mediated associations involving language, emotions, and metaphors. However, stimuli like textures, which are found in both modalities have received less attention. In this study, we conducted two experiments: a free association task and a two alternate forced choice task using everyday tactile textures and sound textures selected from natural sound categories. The results revealed consistent crossmodal associations reported by participants between the textures of the two modalities. They tended to associate more sound textures (e.g., wood shavings and sandpaper) with tactile surfaces that were rated as harder, rougher, and intermediate on the sticky-slippery scale. While some participants based the auditory-tactile association on sensory features, others made the associations based on semantic relationships, co-occurrence in nature, and emotional mediation. Interestingly, the statistical features of the sound textures (mean, variance, kurtosis, power, autocorrelation, and correlation) did not show significant correlations with the crossmodal associations, indicating a higher-level association. This study provides insights into auditory-tactile associations by highlighting the role of sensory and emotional (or cognitive) factors in prompting these associations.

The impact of knitted linked seams on comfort and friction perception.

Friction from knitted clothing can cause discomfort and skin issues, underscoring the importance of tactile comfort for wearers. Seamless knitted garments are assumed to be comfortable to wear, yet there is little understanding of their tactile comfort in comparison to linked seams - the most common form of knitted garment. This novel study examines the influence of a garments knitted structural architecture on clothing comfort and wearability by investigating skin friction and tactile perception across ten body regions in both male and female participants, using two commonly utilised materials and seam designs: cotton and merino wool with plain and linked seams. The impact of seam design and regional factors on skin friction and tactile perception was analysed, revealing varying levels across tested body regions. Removing seams exposed a greater surface area to skin contact, leading to higher perceived friction levels. As such, structural elements in knitted garments enhance wearer comfort.

Seamless knitwear manufacturing offers a more environmentally conscious option compared to traditional cut-and-sew processes. This study investigated the impact of knitted garment material and structure on wearer comfort by analysing skin friction and tactile perception across ten upper body regions. Removing seams increased garment-to-skin contact leading to wearer discomfort.

Respiration, Heartbeat, and Conscious Tactile Perception.

Previous studies have shown that timing of sensory stimulation during the cardiac cycle interacts with perception. Given the natural coupling of respiration and cardiac activity, we investigated here their joint effects on tactile perception. Forty-one healthy female and male human participants reported conscious perception of finger near-threshold electrical pulses (33% null trials) and decision confidence while electrocardiography, respiratory activity, and finger photoplethysmography were recorded. Participants adapted their respiratory cycle to expected stimulus onsets to preferentially occur during late inspiration/early expiration. This closely matched heart rate variation (sinus arrhythmia) across the respiratory cycle such that most frequent stimulation onsets occurred during the period of highest heart rate probably indicating highest alertness and cortical excitability. Tactile detection rate was highest during the first quadrant after expiration onset. Interindividually, stronger respiratory phase-locking to the task was associated with higher detection rates. Regarding the cardiac cycle, we confirmed previous findings that tactile detection rate was higher during diastole than systole and newly specified its minimum at 250-300 ms after the R-peak corresponding to the pulse wave arrival in the finger. Expectation of stimulation induced a transient heart deceleration which was more pronounced for unconfident decision ratings. Interindividually, stronger poststimulus modulations of heart rate were linked to higher detection rates. In summary, we demonstrate how tuning to the respiratory cycle and integration of respiratory-cardiac signals are used to optimize performance of a tactile detection task.SIGNIFICANCE STATEMENT Mechanistic studies on perception and cognition tend to focus on the brain neglecting contributions of the body. Here, we investigated how respiration and heartbeat influence tactile perception: respiration phase-locking to expected stimulus onsets corresponds to highest heart rate (and presumably alertness/cortical excitability) and correlates with detection performance. Tactile detection varies across the heart cycle with a minimum when the pulse reaches the finger and a maximum in diastole. Taken together with our previous finding of unchanged early event-related potentials across the cardiac cycle, we conclude that these effects are not a peripheral physiological artifact but a result of cognitive processes that model our body's internal state, make predictions to guide behavior, and might also tune respiration to serve the task.

An individual's skin stiffness predicts their tactile discrimination of compliance.

Individual differences in tactile acuity have been correlated with age, gender and finger size, whereas the role of the skin's stiffness has been underexplored. Using an approach to image the 3-D deformation of the skin surface during contact with transparent elastic objects, we evaluate a cohort of 40 young participants, who present a diverse range of finger size, skin stiffness and fingerprint ridge breadth. The results indicate that skin stiffness generally correlates with finger size, although individuals with relatively softer skin can better discriminate compliant objects. Analysis of contact at the skin surface reveals that softer skin generates more prominent patterns of deformation, in particular greater rates of change in contact area, which correlate with higher rates of perceptual discrimination of compliance, regardless of finger size. Moreover, upon applying hyaluronic acid to soften individuals' skin, we observe immediate, marked and systematic changes in skin deformation and consequent improvements in perceptual acuity in differentiating compliance. Together, the combination of 3-D imaging of the skin surface, biomechanics measurements, multivariate regression and clustering, and psychophysical experiments show that subtle distinctions in skin stiffness modulate the mechanical signalling of touch and shape individual differences in perceptual acuity. KEY POINTS: Although declines in tactile acuity with ageing are a function of multiple factors, for younger people, the current working hypothesis has been that smaller fingers are better at informing perceptual discrimination because of a higher density of neural afferents. To decouple relative impacts on tactile acuity of skin properties of finger size, skin stiffness, and fingerprint ridge breadth, we combined 3-D imaging of skin surface deformation, biomechanical measurements, multivariate regression and clustering, and psychophysics. The results indicate that skin stiffness generally correlates with finger size, although it more robustly correlates with and predicts an individual's perceptual acuity. In particular, more elastic skin generates higher rates of deformation, which correlate with perceptual discrimination, shown most dramatically by softening each participant's skin with hyaluronic acid. In refining the current working hypothesis, we show the skin's stiffness strongly shapes the signalling of touch and modulates individual differences in perceptual acuity.

Skin properties and afferent density in the deterioration of tactile spatial acuity with age.

Tactile sensitivity is affected by age, as shown by the deterioration of spatial acuity assessed with the two-point discrimination task. This is assumed to be partly a result of age-related changes of the peripheral somatosensory system. In particular, in the elderly, the density of mechanoreceptive afferents decreases with age and the skin tends to become drier, less elastic and less stiff. To assess to what degree mechanoreceptor density, skin hydration, elasticity and stiffness can account for the deterioration of tactile spatial sensitivity observed in the elderly, several approaches were combined, including psychophysics, measurements of finger properties, modelling and simulation of the response of first-order tactile neurons. Psychophysics confirmed that the Elderly group has lower tactile acuity than the Young group. Correlation and commonality analysis showed that age was the most important factor in explaining decreases in behavioural performance. Biological elasticity, hydration and finger pad area were also involved. These results were consistent with the outcome of simulations showing that lower afferent density and lower Young's modulus (i.e. lower stiffness) negatively affected the tactile encoding of stimulus information. Simulations revealed that these changes resulted in a lower build-up of task-relevant stimulus information. Importantly, the reduction in discrimination performance with age in the simulation was less than that observed in the psychophysical testing, indicating that there are additional peripheral as well as central factors responsible for age-related changes in tactile discrimination. KEY POINTS: Ageing effects on tactile perception involve the deterioration of spatial sensitivity, although the contribution of central and peripheral factors is not clear. We combined psychophysics, measurements of finger properties, modelling and simulation of the response of first-order tactile neurons to investigate to what extent skin elasticity, stiffness, hydration, finger pad area and afferent density can account for the lower spatial sensitivity observed in the elderly. Correlation and commonality analysis revealed that age was the most important factor to predict behavioural performance. Skin biological elasticity, hydration and finger pad area contributed to a lesser extent. The simulation of first-order tactile neuron responses indicated that reduction in afferent density plays a major role in the deterioration of tactile spatial acuity. Simulations also showed that lower skin stiffness and lower afferent density affect the build-up of stimulus information and the response of SA1 (i.e. type 1 slowly adapting fibres) and RA1 (i.e. type 1 rapidly adapting fibres) afferent fibres.

Rippling Colloidal Polyelectrolyte Complex for Customized Fingerprints with High Tactile Perception.

Fingerprints possess wide applications in personal identification, tactile perception, access control, and anti-counterfeiting. However, latent fingerprints are usually left on touched surfaces, leading to the leakage of personal information. Furthermore, tactile perception greatly decreases when fingerprints are covered by gloves. Customized fingerprints are developed to solve these issues, but it is a challenge to develop fingerprints with various customized patterns using traditional techniques due to their requiring special templates, materials, or instruments. Inspired by ripples on the lake, blowing air is used to generate surface waves on a colloidal polyelectrolyte complex, leading to vertical stratification and the accumulation of particles near the top of the film layer. As water rapidly evaporates, the viscosity of these particles significantly increases and the wave is solidified, forming fingerprint patterns. These customized fingerprints integrate functions of grasping objects, personal identification without leaving latent fingerprints and tactile perception enhancement, which can be applied in information security, anti-counterfeiting, tactile sensors, and biological engineering.

Electrospun Cellulose Nanocrystals Reinforced Flexible Sensing Paper for Triboelectric Energy Harvesting and Dynamic Self-Powered Tactile Perception.

The technical synergy between flexible sensing paper and triboelectric nanogenerator (TENG) in the next stage of artificial intelligence Internet of Things engineering makes the development of intelligent sensing paper with triboelectric function very attractive. Therefore, it is extremely urgent to explore functional papers that are more suitable for triboelectric sensing. Here, a cellulose nanocrystals (CNCs) reinforced PVDF hybrid paper (CPHP) is developed by electrospinning technology. Benefitting from the unique effects of CNCs, CPHP forms a solid cross-linked network among fibers and obtains a high-strength (25 MPa) paper-like state and high surface roughness. Meanwhile, CNCs also improve the triboelectrification effect of CPHP by assisting the PVDF matrix to form more electroactive phases (96% share) and a higher relative permittivity (17.9). The CPHP-based TENG with single electrode configuration demonstrates good output performance (open-circuit voltage of 116 V, short-circuit current of 2.2 µA and power density of 91 mW m-2 ) and ultrahigh pressure-sensitivity response (3.95 mV Pa-1 ), which endows CPHP with reliable power supply and sensing capability. More importantly, the CPHP-based flexible self-powered tactile sensor with TENG array exhibits multifunctional applications in imitation Morse code compilation, tactile track recognition, and game character control, showing great prospects in the intelligent inductive device and human-machine interaction.

Modulation of somatosensation by transcranial magnetic stimulation over somatosensory cortex: a systematic review.

Over the last three decades, transcranial magnetic stimulation (TMS) has gained popularity as a tool to modulate human somatosensation. However, the effects of different stimulation types on the multiple distinct subdomains of somatosensation (e.g., tactile perception, proprioception and pain) have not been systematically compared. This is especially notable in the case of newer theta-burst stimulation protocols now in widespread use. Here, we aimed to systematically and critically review the existing TMS literature and provide a complete picture of current knowledge regarding the role of TMS in modulating human somatosensation across stimulation protocols and somatosensory domains. Following the PRISMA guidelines, fifty-four studies were included in the current review and were compared based on their methodologies and results. Overall, findings from these studies provide evidence that different types of somatosensation can be both disrupted and enhanced by targeted stimulation of specific somatosensory areas. Some mixed results, however, were reported in the literature. We discussed possible reasons for these mixed results, methodological limitations of existing investigations, and potential avenues for future research.

Study of event-related potentials by withdrawal friction on the fingertip.

OBJECTIVES: The lack of understanding about the brain's reaction processes in perceiving touch and separation between skin and object surfaces is a barrier to the development of existing brain-computer interface technologies and virtual haptics. These technologies are limited in their ability to advance. It leaves prosthesis users with a limited amount of tactile information that they can feel. This study aims to determine whether distinct surface aspects of various items trigger different reactions from the brain when friction is removed from the surface. METHODS: When friction is suddenly removed from the surface of an item, a technique called event-related potential, (ERP) is used to study the features of people's EEGs. It is done after the subject has actively explored the object's surface. A 64-channels EEG collecting system was utilized to acquire EEG data from the individuals. [Corrections added on 5 December 2022, after first online publication: The preceding sentence has been updated.] The event-related potentials for friction removal were generated using the Oddball paradigm, and the samples consisted of sandpaper with three distinct degrees of roughness. We utilized a total of 20 participants, 10 of whom were male, and 10 of whom were female, with a mean age of 21 years. RESULTS: It was discovered that the P3 component of event-related potentials, which is essential for cognition, was noticeably absent in the friction withdrawal response for various roughnesses. It was the case regardless of whether the surface was smooth or rough. Moreover, there was no statistically significant difference between the P1 andP2 components, which suggests that the brain could not recognize the surface properties of objects with varying roughness as the friction withdrawal was being performed. CONCLUSIONS: It has been demonstrated that tactile recognition does not occur after friction withdrawal. The findings of this paper could have significant repercussions for future research involving the study of haptic perception and brain-computer interaction in prosthetic hands. It is a step toward future research on the mechanisms underlying human tactile perception, so think of it as preparation.

The dynamic behavior of skin in response to vibrating touch stimuli affects tactile perception.

BACKGROUND: The tactile perceptions arising on the skin mediate representations of the body and perceptions of the external physical world. Thus, these tactile sensations greatly impact our lives. Although tactile perception is caused by skin deformation, few studies have investigated the contribution of skin physical properties to tactile perception because the skin deformation in response to mechanical stimuli is difficult to measure in real time. In this study, we investigated how the skin deforms in response to externally applied mechanical stimuli and the effect of skin deformation on tactile perception. MATERIALS AND METHODS: Tactile perception was assessed using psychophysical methods. A suction device was used to measure skin deformation in response to mechanical stimuli while assessing tactile perception. The relationship between skin deformation and tactile perception was investigated. RESULTS: Individuals show different skin deformation behavior in response to stimuli of the same intensity, and the amount of skin deformation affects the perceived pressure induced by suction stimulation. Furthermore, when the amount of skin deformation is small, tactile perception becomes more difficult, and the ease of tactile perception varies. CONCLUSION: We argue that dynamic skin behavior is an important factor in tactile perception. Focusing on skin physical characteristics from a constructivist perspective of complex tactile perception may lead to improved tactile communication perception through the control of skin physical properties and realistic tactile presentation in remote environments.

TouchRoller: A Rolling Optical Tactile Sensor for Rapid Assessment of Textures for Large Surface Areas.

Tactile sensing is important for robots to perceive the world as it captures the physical surface properties of the object with which it is in contact and is robust to illumination and colour variances. However, due to the limited sensing area and the resistance of their fixed surface when they are applied with relative motions to the object, current tactile sensors have to tap the tactile sensor on the target object a great number of times when assessing a large surface, i.e., pressing, lifting up, and shifting to another region. This process is ineffective and time-consuming. It is also undesirable to drag such sensors as this often damages the sensitive membrane of the sensor or the object. To address these problems, we propose a roller-based optical tactile sensor named TouchRoller, which can roll around its centre axis. It maintains being in contact with the assessed surface throughout the entire motion, allowing for efficient and continuous measurement. Extensive experiments showed that the TouchRoller sensor can cover a textured surface of 8 cm × 11 cm in a short time of 10 s, much more effectively than a flat optical tactile sensor (in 196 s). The reconstructed map of the texture from the collected tactile images has a high Structural Similarity Index (SSIM) of 0.31 on average when compared with the visual texture. In addition, the contacts on the sensor can be localised with a low localisation error, 2.63 mm in the centre regions and 7.66 mm on average. The proposed sensor will enable the fast assessment of large surfaces with high-resolution tactile sensing and the effective collection of tactile images.

Effects of Sensing Tactile Arrays, Shear Force, and Proprioception of Robot on Texture Recognition.

In robotics, tactile perception is important for fine control using robot grippers and hands. To effectively incorporate tactile perception in robots, it is essential to understand how humans use mechanoreceptors and proprioceptors to perceive texture. Thus, our study aimed to investigate the impact of tactile sensor arrays, shear force, and the positional information of the robot's end effector on its ability to recognize texture. A deep learning network was employed to classify tactile data from 24 different textures that were explored by a robot. The input values of the deep learning network were modified based on variations in the number of channels of the tactile signal, the arrangement of the tactile sensor, the presence or absence of shear force, and the positional information of the robot. By comparing the accuracy of texture recognition, our analysis revealed that tactile sensor arrays more accurately recognized the texture compared to a single tactile sensor. The utilization of shear force and positional information of the robot resulted in an improved accuracy of texture recognition when using a single tactile sensor. Furthermore, an equal number of sensors placed in a vertical arrangement led to a more accurate distinction of textures during exploration when compared to sensors placed in a horizontal arrangement. The results of this study indicate that the implementation of a tactile sensor array should be prioritized over a single sensor for enhanced accuracy in tactile sensing, and the use of integrated data should be considered for single tactile sensing.

Revealing the Meissner Corpuscles in Human Glabrous Skin Using In Vivo Non-Invasive Imaging Techniques.

The presence of mechanoreceptors in glabrous skin allows humans to discriminate textures by touch. The amount and distribution of these receptors defines our tactile sensitivity and can be affected by diseases such as diabetes, HIV-related pathologies, and hereditary neuropathies. The quantification of mechanoreceptors as clinical markers by biopsy is an invasive method of diagnosis. We report the localization and quantification of Meissner corpuscles in glabrous skin using in vivo, non-invasive optical microscopy techniques. Our approach is supported by the discovery of epidermal protrusions which are co-localized with Meissner corpuscles. Index fingers, small fingers, and tenar palm regions of ten participants were imaged by optical coherence tomography (OCT) and laser scan microscopy (LSM) to determine the thickness of the stratum corneum and epidermis and to count the Meissner corpuscles. We discovered that regions containing Meissner corpuscles could be easily identified by LSM with an enhanced optical reflectance above the corpuscles, caused by a protrusion of the strongly reflecting epidermis into the stratum corneum with its weak reflectance. We suggest that this local morphology above Meissner corpuscles has a function in tactile perception.

Body mapping of skin friction coefficient and tactile perception during the dynamic skin-textile interaction.

The clothing fabric and skin interact continuously across the many regions of users' bodies during wear, which can lead to both physical skin damage and discomfort. Therefore, this investigation aimed to explore the regional differences in skin friction, tactile perception, and sensitivity in both females and males during the skin-textile interaction. The static and dynamic friction coefficient and textile perception (texture, stickiness, pleasantness, and discomfort) were measured across the 36 selected testing body areas by using a friction measurement device. The results revealed there was a significant difference in skin friction, tactile perceptions, and sensitivity across the various body regions. The anterior neck had the highest skin friction in both females and males, and participants generally rated higher texture perception in their anterior aspects compared to posterior and lateral regions. There was no significant difference in skin friction, tactile perception ratings, and sensitivity between females and males. Practitioner summary: This study sought to examine regional variations in skin friction, tactile perception, and sensitivity during the skin-textile interaction. There was a significant difference in skin friction, tactile perceptions, and sensitivity across the various body regions and no significant sex effect on skin friction, tactile perception ratings, and sensitivity.

Multidigit tactile perception I: motion integration benefits for tactile trajectories presented bimanually.

Interactions with objects involve simultaneous contact with multiple, not necessarily adjacent, skin regions. Although advances have been made in understanding the capacity to selectively attend to a single tactile element among distracting stimulations, here, we examine how multiple stimulus elements are explicitly integrated into an overall tactile percept. Across four experiments, participants averaged the direction of two simultaneous tactile motion trajectories of varying discrepancy delivered to different fingerpads. Averaging performance differed between within- and between-hands conditions in terms of sensitivity and precision but was unaffected by somatotopic proximity between stimulated fingers. First, precision was greater in between-hand compared with within-hand conditions, demonstrating a bimanual perceptual advantage in multi-touch integration. Second, sensitivity to the average direction was influenced by the discrepancy between individual motion signals, but only for within-hand conditions. Overall, our experiments identify key factors that influence perception of simultaneous tactile events. In particular, we show that multi-touch integration is constrained by hand-specific rather than digit-specific mechanisms.NEW & NOTEWORTHY Object manipulation involves encoding spatially and temporally extended tactile signals, yet most studies emphasize minimal units of tactile perception (e.g., selectivity). Instead, we asked participants to average two tactile motion trajectories delivered simultaneously to two different fingerpads. Our results show strong integration between multiple tactile inputs, but subject to limitations for inputs delivered within a hand. As such, the present study establishes a paradigm for studying unified experience of touch despite distinct stimulus elements.