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Tian X, Cheng G, Wu Z, Wen X, Kong Y, Long P, Zhao F, Li Z, Zhang D, Hu Y, Wei D. High‐Resolution Carbon‐Based Tactile Sensor Array for Dynamic Pulse Imaging. ADVANCED FUNCTIONAL MATERIALS 2024. [DOI: 10.1002/adfm.202406022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2024] [Indexed: 09/14/2024]
Abstract
AbstractWith the development of modern medicine, the importance of continuous and reliable pulse wave monitoring has increased significantly in physiological evaluation and disease diagnosis. Among them, the 3D reconstruction of the pulse wave is indispensable, and needs rely on ultra‐high resolution sensor arrays, that is, high spatial resolution, temporal resolution, and force resolution. Herein, a flexible high‐density 32 × 32 tactile sensor array based on pressure‐sensitive tunneling mechanism is develpoed. Conformal graphene nanowalls (GNWs) pattern arrays are deposited on micro‐pyramidal structural Si substrate via mask‐assisted plasma enhanced chemical vapor deposition (PECVD) method and are adopted as pressure‐sensitive electrode, exhibiting a spatial resolution of 64 dots/cm2, high sensitivity (222.36 kPa−1) and short response time (2 ms). More importantly, HfO2 tunneling layer can effectively suppress noise current, which made it sense weak pressure signals with 1/1000 force resolution and SNR of 36.32 dB. By leveraging its high‐resolution array, more holistic pulse signals are acquired and the 3D shape of the pulse wave are successfully replicated. This work shows high‐resolution sensors have significant promise for applications in remote intelligent diagnostics.
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Affiliation(s)
- Xin Tian
- Chongqing Key Laboratory of Generic Technology and System of Service Robots, Chongqing Institute of Green and Intelligent Technology Chinese Academy of Sciences Chongqing 400714 China
| | - Guanyin Cheng
- Chongqing Key Laboratory of Generic Technology and System of Service Robots, Chongqing Institute of Green and Intelligent Technology Chinese Academy of Sciences Chongqing 400714 China
| | - Zhonghuai Wu
- The MIIT Key Laboratory of Complex‐Field Intelligent Exploration School of Optics and Photonics Beijing Institute of Technology Beijing 100081 China
| | - Xudong Wen
- College of Medicine Southwest Jiaotong University Chengdu 610031 China
| | - Yongkang Kong
- Chongqing Key Laboratory of Generic Technology and System of Service Robots, Chongqing Institute of Green and Intelligent Technology Chinese Academy of Sciences Chongqing 400714 China
| | - Pan Long
- College of Medicine Southwest Jiaotong University Chengdu 610031 China
| | - Fubang Zhao
- Chongqing Key Laboratory of Generic Technology and System of Service Robots, Chongqing Institute of Green and Intelligent Technology Chinese Academy of Sciences Chongqing 400714 China
| | - Zhongxiang Li
- The MIIT Key Laboratory of Complex‐Field Intelligent Exploration School of Optics and Photonics Beijing Institute of Technology Beijing 100081 China
| | - Dong Zhang
- Xiyuan Hospital of China Academy of Chinese Medical Sciences Beijing 100091 China
| | - Yonghe Hu
- College of Medicine Southwest Jiaotong University Chengdu 610031 China
| | - Dapeng Wei
- Chongqing Key Laboratory of Generic Technology and System of Service Robots, Chongqing Institute of Green and Intelligent Technology Chinese Academy of Sciences Chongqing 400714 China
- State Key Laboratory of Trauma and Chemical Poisoning Third Military Medical University Chongqing 400042 China
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Afzal N, du Bois de Dunilac S, Loutit AJ, Shea HO, Ulloa PM, Khamis H, Vickery RM, Wiertlewski M, Redmond SJ, Birznieks I. Role of arm reaching movement kinematics in friction perception at initial contact with smooth surfaces. J Physiol 2024; 602:2089-2106. [PMID: 38544437 DOI: 10.1113/jp286027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2023] [Accepted: 03/12/2024] [Indexed: 05/04/2024] Open
Abstract
When manipulating objects, humans begin adjusting their grip force to friction within 100 ms of contact. During motor adaptation, subjects become aware of the slipperiness of touched surfaces. Previously, we have demonstrated that humans cannot perceive frictional differences when surfaces are brought in contact with an immobilised finger, but can do so when there is submillimeter lateral displacement or subjects actively make the contact movement. Similarly, in, we investigated how humans perceive friction in the absence of intentional exploratory sliding or rubbing movements, to mimic object manipulation interactions. We used a two-alternative forced-choice paradigm in which subjects had to reach and touch one surface followed by another, and then indicate which felt more slippery. Subjects correctly identified the more slippery surface in 87 ± 8% of cases (mean ± SD; n = 12). Biomechanical analysis of finger pad skin displacement patterns revealed the presence of tiny (<1 mm) localised slips, known to be sufficient to perceive frictional differences. We tested whether these skin movements arise as a result of natural hand reaching kinematics. The task was repeated with the introduction of a hand support, eliminating the hand reaching movement and minimising fingertip movement deviations from a straight path. As a result, our subjects' performance significantly declined (66 ± 12% correct, mean ± SD; n = 12), suggesting that unrestricted reaching movement kinematics and factors such as physiological tremor, play a crucial role in enhancing or enabling friction perception upon initial contact. KEY POINTS: More slippery objects require a stronger grip to prevent them from slipping out of hands. Grip force adjustments to friction driven by tactile sensory signals are largely automatic and do not necessitate cognitive involvement; nevertheless, some associated awareness of grip surface slipperiness under such sensory conditions is present and helps to select a safe and appropriate movement plan. When gripping an object, tactile receptors provide frictional information without intentional rubbing or sliding fingers over the surface. However, we have discovered that submillimeter range lateral displacement might be required to enhance or enable friction sensing. The present study provides evidence that such small lateral movements causing localised partial slips arise and are an inherent part of natural reaching movement kinematics.
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Affiliation(s)
- Naqash Afzal
- School of Biomedical Sciences, UNSW Sydney, Sydney, NSW, Australia
- Neuroscience Research Australia, Sydney, NSW, Australia
- Department of Mechanical Engineering, Khalifa University, Abu Dhabi, United Arab Emirates
- Center for Autonomous Robotic Systems, Khalifa University, Abu Dhabi, United Arab Emirates
| | | | - Alastair J Loutit
- School of Biomedical Sciences, UNSW Sydney, Sydney, NSW, Australia
- Neuroscience Research Australia, Sydney, NSW, Australia
| | - Helen O Shea
- Department of Psychology, University of Limerick, Limerick, Ireland
| | - Pablo Martinez Ulloa
- School of Electrical and Electronic Engineering, University College Dublin, Dublin, Ireland
| | - Heba Khamis
- Graduate School of Biomedical Engineering, UNSW Sydney, Sydney, NSW, Australia
| | - Richard M Vickery
- School of Biomedical Sciences, UNSW Sydney, Sydney, NSW, Australia
- Neuroscience Research Australia, Sydney, NSW, Australia
- Bionics and Biorobotics, Tyree Foundation Institute of Health Engineering, UNSW Sydney, Sydney, NSW, Australia
| | - Michaël Wiertlewski
- Department of Cognitive Robotics, Delft University of Technology, Delft, The Netherlands
| | - Stephen J Redmond
- School of Electrical and Electronic Engineering, University College Dublin, Dublin, Ireland
| | - Ingvars Birznieks
- School of Biomedical Sciences, UNSW Sydney, Sydney, NSW, Australia
- Neuroscience Research Australia, Sydney, NSW, Australia
- Bionics and Biorobotics, Tyree Foundation Institute of Health Engineering, UNSW Sydney, Sydney, NSW, Australia
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3
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Mete M, Jeong H, Wang WD, Paik J. SORI: A softness-rendering interface to unravel the nature of softness perception. Proc Natl Acad Sci U S A 2024; 121:e2314901121. [PMID: 38466880 PMCID: PMC10990105 DOI: 10.1073/pnas.2314901121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2023] [Accepted: 02/02/2024] [Indexed: 03/13/2024] Open
Abstract
Tactile perception of softness serves a critical role in the survival, well-being, and social interaction among various species, including humans. This perception informs activities from food selection in animals to medical palpation for disease detection in humans. Despite its fundamental importance, a comprehensive understanding of how softness is neurologically and cognitively processed remains elusive. Previous research has demonstrated that the somatosensory system leverages both cutaneous and kinesthetic cues for the sensation of softness. Factors such as contact area, depth, and force play a particularly critical role in sensations experienced at the fingertips. Yet, existing haptic technologies designed to explore this phenomenon are limited, as they often couple force and contact area, failing to provide a real-world experience of softness perception. Our research introduces the softness-rendering interface (SORI), a haptic softness display designed to bridge this knowledge gap. Unlike its predecessors, SORI has the unique ability to decouple contact area and force, thereby allowing for a quantitative representation of softness sensations at the fingertips. Furthermore, SORI incorporates individual physical fingertip properties and model-based softness cue estimation and mapping to provide a highly personalized experience. Utilizing this method, SORI quantitatively replicates the sensation of softness on stationary, dynamic, homogeneous, and heterogeneous surfaces. We demonstrate that SORI accurately renders the surfaces of both virtual and daily objects, thereby presenting opportunities across a range of fields, from teleoperation to medical technology. Finally, our proposed method and SORI will expedite psychological and neuroscience research to unlock the nature of softness perception.
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Affiliation(s)
- Mustafa Mete
- Reconfigurable Robotics Laboratory, Institute of Mechanical Engineering, School of Engineering, École Polytechnique Fédérale de Lausanne, LausanneCH 1005, Switzerland
| | - Haewon Jeong
- Soft Robotics Laboratory, Department of Mechanical Engineering, College of Engineering, Hanyang University, Seoul04763, Republic of Korea
| | - Wei Dawid Wang
- Soft Robotics Laboratory, Department of Mechanical Engineering, College of Engineering, Hanyang University, Seoul04763, Republic of Korea
| | - Jamie Paik
- Reconfigurable Robotics Laboratory, Institute of Mechanical Engineering, School of Engineering, École Polytechnique Fédérale de Lausanne, LausanneCH 1005, Switzerland
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Delhaye BP, Schiltz F, Crevecoeur F, Thonnard JL, Lefèvre P. Fast grip force adaptation to friction relies on localized fingerpad strains. SCIENCE ADVANCES 2024; 10:eadh9344. [PMID: 38232162 DOI: 10.1126/sciadv.adh9344] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/23/2023] [Accepted: 12/18/2023] [Indexed: 01/19/2024]
Abstract
During object manipulation, humans adjust the grip force to friction, such that slippery objects are squeezed more firmly than sticky ones. This essential mechanism to keep a stable grasp relies on feedback from tactile afferents innervating the fingertips, that are sensitive to local skin strains. To test if this feedback originates from the skin-object interface, we asked participants to perform a grip-lift task with an instrumented object able to monitor skin strains at the contact through transparent plates of different frictions. We observed that, following an unbeknown change in plate across trials, participants adapted their grip force to friction. After switching from high to low friction, we found a significant increase in strain inside the contact arising ~100 ms before the modulation of grip force, suggesting that differences in strain patterns before lift-off are used by the nervous system to quickly adjust the force to the frictional properties of manipulated objects.
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Affiliation(s)
- Benoit P Delhaye
- Institute of Neuroscience, Université catholique de Louvain, Brussels, Belgium
- Institute of Information and Communication Technologies, Electronics and Applied Mathematics, Université catholique de Louvain, Louvain-la-Neuve, Belgium
| | - Félicien Schiltz
- Institute of Neuroscience, Université catholique de Louvain, Brussels, Belgium
- Institute of Information and Communication Technologies, Electronics and Applied Mathematics, Université catholique de Louvain, Louvain-la-Neuve, Belgium
| | - Frédéric Crevecoeur
- Institute of Neuroscience, Université catholique de Louvain, Brussels, Belgium
- Institute of Information and Communication Technologies, Electronics and Applied Mathematics, Université catholique de Louvain, Louvain-la-Neuve, Belgium
| | - Jean-Louis Thonnard
- Institute of Neuroscience, Université catholique de Louvain, Brussels, Belgium
- Institute of Information and Communication Technologies, Electronics and Applied Mathematics, Université catholique de Louvain, Louvain-la-Neuve, Belgium
| | - Philippe Lefèvre
- Institute of Neuroscience, Université catholique de Louvain, Brussels, Belgium
- Institute of Information and Communication Technologies, Electronics and Applied Mathematics, Université catholique de Louvain, Louvain-la-Neuve, Belgium
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Ali Y, Montani V, Cesari P. Neural underpinnings of the interplay between actual touch and action imagination in social contexts. Front Hum Neurosci 2024; 17:1274299. [PMID: 38292652 PMCID: PMC10826515 DOI: 10.3389/fnhum.2023.1274299] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2023] [Accepted: 12/21/2023] [Indexed: 02/01/2024] Open
Abstract
While there is established evidence supporting the involvement of the sense of touch in various actions, the neural underpinnings of touch and action interplay in a social context remain poorly understood. To prospectively investigate this phenomenon and offer further insights, we employed a combination of motor and sensory components by asking participants to imagine exerting force with the index finger while experiencing their own touch, the touch of one another individual, the touch of a surface, and no touch. Based on the assumption that the patterns of activation in the motor system are similar when action is imagined or actually performed, we proceeded to apply a single-pulse transcranial magnetic stimulation over the primary motor cortex (M1) while participants engaged in the act of imagination. Touch experience was associated with higher M1 excitability in the presence and in the absence of force production imagination, but only during force production imagination M1 excitability differed among the types of touch: both biological sources, the self-touch and the touch of one other individual, elicited a significant increase in motor system activity when compared to touching a non-living surface or in the absence of touch. A strong correlation between individual touch avoidance questionnaire values and facilitation in the motor system was present while touching another person, indicating a social aspect for touch in action. The present study unveils the motor system correlates when the sensory/motor components of touch are considered in social contexts.
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Affiliation(s)
| | | | - Paola Cesari
- Department of Neuroscience, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
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Loutit AJ, Wheat HE, Khamis H, Vickery RM, Macefield VG, Birznieks I. How Tactile Afferents in the Human Fingerpad Encode Tangential Torques Associated with Manipulation: Are Monkeys Better than Us? J Neurosci 2023; 43:4033-4046. [PMID: 37142429 PMCID: PMC10254986 DOI: 10.1523/jneurosci.1305-22.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2022] [Revised: 04/14/2023] [Accepted: 04/17/2023] [Indexed: 05/06/2023] Open
Abstract
Dexterous object manipulation depends critically on information about forces normal and tangential to the fingerpads, and also on torque associated with object orientation at grip surfaces. We investigated how torque information is encoded by human tactile afferents in the fingerpads and compared them to 97 afferents recorded in monkeys (n = 3; 2 females) in our previous study. Human data included slowly-adapting Type-II (SA-II) afferents, which are absent in the glabrous skin of monkeys. Torques of different magnitudes (3.5-7.5 mNm) were applied in clockwise and anticlockwise directions to a standard central site on the fingerpads of 34 human subjects (19 females). Torques were superimposed on a 2, 3, or 4 N background normal force. Unitary recordings were made from fast-adapting Type-I (FA-I, n = 39), and slowly-adapting Type-I (SA-I, n = 31) and Type-II (SA-II, n = 13) afferents supplying the fingerpads via microelectrodes inserted into the median nerve. All three afferent types encoded torque magnitude and direction, with torque sensitivity being higher with smaller normal forces. SA-I afferent responses to static torque were inferior to dynamic stimuli in humans, while in monkeys the opposite was true. In humans this might be compensated by the addition of sustained SA-II afferent input, and their capacity to increase or decrease firing rates with direction of rotation. We conclude that the discrimination capacity of individual afferents of each type was inferior in humans than monkeys which could be because of differences in fingertip tissue compliance and skin friction.SIGNIFICANCE STATEMENT We investigated how individual human tactile nerve fibers encode rotational forces (torques) and compared them to their monkey counterparts. Human hands, but not monkey hands, are innervated by a tactile neuron type (SA-II afferents) specialized to encode directional skin strain yet, so far, torque encoding has only been studied in monkeys. We find that human SA-I afferents were generally less sensitive and less able to discriminate torque magnitude and direction than their monkey counterparts, especially during the static phase of torque loading. However, this shortfall in humans could be compensated by SA-II afferent input. This indicates that variation in afferent types might complement each other signaling different stimulus features possibly providing computational advantage to discriminate stimuli.
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Affiliation(s)
- Alastair J Loutit
- Neuroscience Research Australia, Sydney, New South Wales 2031, Australia
- School of Biomedical Sciences, UNSW Sydney, Sydney, New South Wales 2031, Australia
| | - Heather E Wheat
- Department of Anatomy and Physiology, University of Melbourne, Melbourne, Victoria 3052, Australia
| | - Heba Khamis
- Neuroscience Research Australia, Sydney, New South Wales 2031, Australia
- Graduate School of Biomedical Engineering, UNSW Sydney, Sydney, New South Wales 2031, Australia
| | - Richard M Vickery
- Neuroscience Research Australia, Sydney, New South Wales 2031, Australia
- School of Biomedical Sciences, UNSW Sydney, Sydney, New South Wales 2031, Australia
- Bionics and Bio-robotics, Tyree Foundation Institute of Health Engineering, UNSW Sydney, Sydney, New South Wales 2031, Australia
| | - Vaughan G Macefield
- Baker Heart and Diabetes Institute, Melbourne, Victoria 3004, Australia
- Department of Anatomy and Physiology, University of Melbourne, Melbourne, Victoria 3052, Australia
- Department of Neuroscience, Monash University, Melbourne, Victoria 3052, Australia
| | - Ingvars Birznieks
- Neuroscience Research Australia, Sydney, New South Wales 2031, Australia
- School of Biomedical Sciences, UNSW Sydney, Sydney, New South Wales 2031, Australia
- Bionics and Bio-robotics, Tyree Foundation Institute of Health Engineering, UNSW Sydney, Sydney, New South Wales 2031, Australia
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Li B, Hauser SC, Gerling GJ. Faster Indentation Influences Skin Deformation To Reduce Tactile Discriminability of Compliant Objects. IEEE TRANSACTIONS ON HAPTICS 2023; 16:215-227. [PMID: 37028048 PMCID: PMC10357367 DOI: 10.1109/toh.2023.3253256] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/19/2023]
Abstract
To discriminate the compliance of soft objects, we rely upon spatiotemporal cues in the mechanical deformation of the skin. However, we have few direct observations of skin deformation over time, in particular how its response differs with indentation velocities and depths, and thereby helps inform our perceptual judgments. To help fill this gap, we develop a 3D stereo imaging method to observe contact of the skin's surface with transparent, compliant stimuli. Experiments with human-subjects, in passive touch, are conducted with stimuli varying in compliance, indentation depth, velocity, and time duration. The results indicate that contact durations greater than 0.4 s are perceptually discriminable. Moreover, compliant pairs delivered at higher velocities are more difficult to discriminate because they induce smaller differences in deformation. In a detailed quantification of the skin's surface deformation, we find that several, independent cues aid perception. In particular, the rate of change of gross contact area best correlates with discriminability, across indentation velocities and compliances. However, cues associated with skin surface curvature and bulk force are also predictive, for stimuli more and less compliant than skin, respectively. These findings and detailed measurements seek to inform the design of haptic interfaces.
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du Bois de Dunilac S, Córdova Bulens D, Lefèvre P, Redmond SJ, Delhaye BP. Biomechanics of the finger pad in response to torsion. J R Soc Interface 2023; 20:20220809. [PMID: 37073518 PMCID: PMC10113816 DOI: 10.1098/rsif.2022.0809] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2022] [Accepted: 03/24/2023] [Indexed: 04/20/2023] Open
Abstract
Surface skin deformation of the finger pad during partial slippage at finger-object interfaces elicits firing of the tactile sensory afferents. A torque around the contact normal is often present during object manipulation, which can cause partial rotational slippage. Until now, studies of surface skin deformation have used stimuli sliding rectilinearly and tangentially to the skin. Here, we study surface skin dynamics under pure torsion of the right index finger of seven adult participants (four males). A custom robotic platform stimulated the finger pad with a flat clean glass surface, controlling the normal forces and rotation speeds applied while monitoring the contact interface using optical imaging. We tested normal forces between 0.5 N and 10 N at a fixed angular velocity of 20° s-1 and angular velocities between 5° s-1 and 100° s-1 at a fixed normal force of 2 N. We observe the characteristic pattern by which partial slips develop, starting at the periphery of the contact and propagating towards its centre, and the resulting surface strains. The 20-fold range of normal forces and angular velocities used highlights the effect of those parameters on the resulting torque and skin strains. Increasing normal force increases the contact area, the generated torque, strains and the twist angle required to reach full slip. On the other hand, increasing angular velocity causes more loss of contact at the periphery and higher strain rates (although it has no impact on resulting strains after the full rotation). We also discuss the surprisingly large inter-individual variability in skin biomechanics, notably observed in the twist angle the stimulus needs to rotate before reaching full slip.
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Affiliation(s)
- Sophie du Bois de Dunilac
- School of Electrical and Electronic Engineering, University College Dublin, Belfield, Dublin 4, Ireland
| | - David Córdova Bulens
- School of Electrical and Electronic Engineering, University College Dublin, Belfield, Dublin 4, Ireland
| | - Philippe Lefèvre
- Institute of Information and Communication Technologies, Electronics and Applied Mathematics (ICTEAM), and Institute of Neuroscience (IoNS), Université catholique de Louvain, 1348 Louvain-la-Neuve and 1200 Brussels, Belgium
| | - Stephen J. Redmond
- School of Electrical and Electronic Engineering, University College Dublin, Belfield, Dublin 4, Ireland
| | - Benoit P. Delhaye
- Institute of Information and Communication Technologies, Electronics and Applied Mathematics (ICTEAM), and Institute of Neuroscience (IoNS), Université catholique de Louvain, 1348 Louvain-la-Neuve and 1200 Brussels, Belgium
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Monnoyer J, Willemet L, Wiertlewski M. Rapid change of friction causes the illusion of touching a receding surface. J R Soc Interface 2023; 20:20220718. [PMID: 36751927 PMCID: PMC9905974 DOI: 10.1098/rsif.2022.0718] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2022] [Accepted: 01/09/2023] [Indexed: 02/09/2023] Open
Abstract
Shortly after touching an object, humans can tactually gauge the frictional resistance of a surface. The knowledge of surface friction is paramount to tactile perception and the motor control of grasp. While potent correlations between friction and participants' perceptual response have been found, the causal link between the friction of the surface, its evolution and its perceptual experience has yet to be demonstrated. Here, we leverage new experimental apparatus able to modify friction in real time, to show that participants can perceive sudden changes in friction when they are pressing on a surface. Surprisingly, only a reduction of the friction coefficient leads to a robust perception. High-speed imaging data indicate that the sensation is caused by a release of a latent elastic strain over a 20 ms timeframe after the activation of the friction-reduction device. This rapid change of frictional properties during initial contact is interpreted as a normal displacement of the surface, which paves the way for haptic surfaces that can produce illusions of interacting with mechanical buttons.
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Affiliation(s)
- Jocelyn Monnoyer
- Aix-Marseille University, CNRS, ISM, Marseille, France
- Stellantis, Human Factors Group, Velizy, France
| | - Laurence Willemet
- Cognitive Robotics Department, Delft University of Technology, Delft, The Netherlands
| | - Michaël Wiertlewski
- Cognitive Robotics Department, Delft University of Technology, Delft, The Netherlands
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Serhat G, Vardar Y, Kuchenbecker KJ. Contact evolution of dry and hydrated fingertips at initial touch. PLoS One 2022; 17:e0269722. [PMID: 35830372 PMCID: PMC9278764 DOI: 10.1371/journal.pone.0269722] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2021] [Accepted: 05/26/2022] [Indexed: 11/19/2022] Open
Abstract
Pressing the fingertips into surfaces causes skin deformations that enable humans to grip objects and sense their physical properties. This process involves intricate finger geometry, non-uniform tissue properties, and moisture, complicating the underlying contact mechanics. Here we explore the initial contact evolution of dry and hydrated fingers to isolate the roles of governing physical factors. Two participants gradually pressed an index finger on a glass surface under three moisture conditions: dry, water-hydrated, and glycerin-hydrated. Gross and real contact area were optically measured over time, revealing that glycerin hydration produced strikingly higher real contact area, while gross contact area was similar for all conditions. To elucidate the causes for this phenomenon, we investigated the combined effects of tissue elasticity, skin-surface friction, and fingerprint ridges on contact area using simulation. Our analyses show the dominant influence of elastic modulus over friction and an unusual contact phenomenon, which we call friction-induced hinging.
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Affiliation(s)
- Gokhan Serhat
- Haptic Intelligence Department, Max Planck Institute for Intelligent Systems, Stuttgart, Germany
- * E-mail:
| | - Yasemin Vardar
- Haptic Intelligence Department, Max Planck Institute for Intelligent Systems, Stuttgart, Germany
- Department of Cognitive Robotics, Delft University of Technology, Delft, CD, The Netherlands
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11
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Normal and tangential forces combine to convey contact pressure during dynamic tactile stimulation. Sci Rep 2022; 12:8215. [PMID: 35581308 PMCID: PMC9114425 DOI: 10.1038/s41598-022-12010-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2021] [Accepted: 04/26/2022] [Indexed: 11/09/2022] Open
Abstract
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.
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Afzal N, Stubbs E, Khamis H, Loutit AJ, Redmond SJ, Vickery RM, Wiertlewski M, Birznieks I. Submillimeter Lateral Displacement Enables Friction Sensing and Awareness of Surface Slipperiness. IEEE TRANSACTIONS ON HAPTICS 2022; 15:20-25. [PMID: 34982692 DOI: 10.1109/toh.2021.3139890] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Human tactile perception and motor control rely on the frictional estimates that stem from the deformation of the skin and slip events. However, it is not clear how exactly these mechanical events relate to the perception of friction. This study aims to quantify how minor lateral displacement and speed enables subjects to feel frictional differences. In a 2-alternative forced-choice protocol, an ultrasonic friction-reduction device was brought in contact perpendicular to the skin surface of an immobilized index finger; after reaching 1N normal force, the plate was moved laterally. A combination of four displacement magnitudes (0.2, 0.5, 1.2 and 2 mm), two levels of friction (high, low) and three displacement speeds (1, 5 and 10 mm/s) were tested. We found that the perception of frictional difference was enabled by submillimeter range lateral displacement. Friction discrimination thresholds were reached with lateral displacements ranging from 0.2 to 0.5 mm and surprisingly speed had only a marginal effect. These results demonstrate that partial slips are sufficient to cause awareness of surface slipperiness. These quantitative data are crucial for designing haptic devices that render slipperiness. The results also show the importance of subtle lateral finger movements present during dexterous manipulation tasks.
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