Tactile Sensory Feedback Research Articles

Selective intrafascicular stimulation of myelinated and unmyelinated nerve fibers through a longitudinal electrode: A computational study

Carbon nanotube (CNT) fiber electrodes have demonstrated exceptional spatial selectivity and sustained reliability in the context of intrafascicular electrical stimulation, as evidenced through rigorous animal experimentation. A significant presence of unmyelinated C fibers, known to induce uncomfortable somatosensory experiences, exists within peripheral nerves. This presence poses a considerable challenge to the excitation of myelinated Aβ fibers, which are crucial for tactile sensation. To achieve nuanced tactile sensory feedback utilizing CNT fiber electrodes, the selective stimulation of Aβ sensory afferents emerges as a critical factor.In confronting this challenge, the present investigation sought to refine and apply a rat sciatic-nerve model leveraging the capabilities of the COMSOL-NEURON framework. This approach enables a systematic evaluation of the influence exerted by stimulation parameters and electrode geometry on the activation dynamics of both myelinated Aβ and unmyelinated C fibers. The findings advocate for the utilization of current pulses featuring a pulse width of 600 μs, alongside the deployment of CNT fibers characterized by a diminutive diameter of 10 μm, with an exclusively exposed cross-sectional area, to facilitate reduced activation current thresholds. Comparative analysis under monopolar and bipolar electrical stimulation conditions revealed proximate activation thresholds, albeit with bipolar stimulation exhibiting superior fiber selectivity relative to its monopolar counterpart. Concerning pulse waveform characteristics, the adoption of an anodic-first biphasic stimulation modality is favored, taking into account the dual criteria of activation threshold and fiber selectivity optimization. Consequently, this investigation furnishes an efficacious stimulation paradigm for the selective activation of touch-related nerve fibers, alongside provisioning a comprehensive theoretical foundation for the realization of natural tactile feedback within the domain of prosthetic hand applications.

Closed-Loop Force Control by Biorealistic Hand Prosthesis with Visual and Tactile Sensory Feedback.

The ability of a novel biorealistic hand prosthesis for grasp force control reveals improved neural compatibility between the human-prosthetic interaction. The primary purpose here was to validate a virtual training platform for amputee subjects and evaluate the respective roles of visual and tactile information in fundamental force control tasks. We developed a digital twin of tendon-driven prosthetic hand in the MuJoCo environment. Biorealistic controllers emulated a pair of antagonistic muscles controlling the index finger of the virtual hand by surface electromyographic (sEMG) signals from amputees' residual forearm muscles. Grasp force information was transmitted to amputees through evoked tactile sensation (ETS) feedback. Six forearm amputees participated in force tracking and holding tasks under different feedback conditions or using their intact hands. Test results showed that visual feedback played a predominant role than ETS feedback in force tracking and holding tasks. However, in the absence of visual feedback during the force holding task, ETS feedback significantly enhanced motor performance compared to feedforward control alone. Thus, ETS feedback still supplied reliable sensory information to facilitate amputee's ability of stable grasp force control. The effects of tactile and visual feedback on force control were subject-specific when both types of feedback were provided simultaneously. Amputees were able to integrate visual and tactile information to the biorealistic controllers and achieve a good sensorimotor performance in grasp force regulation. The virtual platform may provide a training paradigm for amputees to adapt the biorealistic hand controller and ETS feedback optimally.

Open-Source Instrumented Object to Study Dexterous Object Manipulation.

Humans use tactile feedback to perform skillful manipulation. When tactile sensory feedback is unavailable, for instance, if the fingers are anesthetized, dexterity is severely impaired. Imaging the deformation of the finger pad skin when in contact with a transparent plate provides information about the tactile feedback received by the central nervous system. Indeed, skin deformations are transduced into neural signals by the mechanoreceptors of the finger pad skin. Understanding how this feedback is used for active object manipulation would improve our understanding of human dexterity. In this paper, we present a new device for imaging the skin of the finger pad of one finger during manipulation performed with a precision grip. The device's mass (300 g) makes it easy to use during unconstrained dexterous manipulation. Using this device, we reproduced the experiment performed in Delhaye et al. (2021) We extracted the strains aligned with the object's movement, i.e., the vertical strains in the ulnar and radial parts of the fingerpad, to see how correlated they were with the grip force (GF) adaptation. Interestingly, parts of our results differed from those in Delhaye et al. (2021) due to weight and inertia differences between the devices, with average GF across participants differing significantly. Our results highlight a large variability in the behavior of the skin across participants, with generally low correlations between strain and GF adjustments, suggesting that skin deformations are not the primary driver of GF adaptation in this manipulation scenario.

FPGA-Based Tactile Sensory Platform with Optical Fiber Data Link for Feedback Systems in Prosthetics

In this paper, we propose and validate a tactile sensory feedback system for prosthetic applications based on an optical communication link. The optical link features a low power and wide transmission bandwidth, which makes the feedback system suitable for a large number and variety of tactile sensors. The low-power transmission is derived from the employed UWB-based optical modulation technique. A system prototype, consisting of digital transmitter and receiver boards and acquisition circuits to interface 32 piezoelectric sensors, was implemented and experimentally tested. The system functionality was demonstrated by processing and transmitting data from the piezoelectric sensor at a 100 Mbps data rate through the optical link, measuring a communication energy consumption of 50 pJ/bit. The reported experimental results validate the functionality of the proposed sensory feedback system and demonstrate its real-time operation capabilities.

Design and Experimental Evaluation of a Sensorimotor-inspired Grasping Strategy for Dexterous Prosthetic Hands.

Stable grasping without slips or crushing is a major challenge for amputees who lose the natural sensorimotor system in dynamically changing daily life environments. Amputees rely largely on visual cues to control the prosthetic hand to complete daily living activities due to a lack of haptic feedback. The human tactile sense can simultaneously feel normal and shear forces. When grasping objects based on the anticipated load conditions, the human hand adjusts the grasping force in real time based on shear force feedback. Here, a sensorimotor-inspired grasping strategy for a dexterous prosthetic hand is proposed to improve grasping performance. The proposed grasping strategy allows the amputee to intuitively control the prosthetic hand. The dexterous prosthetic hand can adaptively adjust the grasp force based on tactile sensory feedback to simultaneously prevent the slipping of objects with unknown shapes, weight, roughness, and softness. Experiments show that the myoelectrical prosthetic hand has grasping force adaptive adjustment and slip prevention ability and provides improved grasping compared to prosthetics with traditional open-loop control.

Soft, All‐Polymer Optoelectronic Tactile Sensor for Stick‐Slip Detection

AbstractThe mechanoreceptors of the human tactile sensory system contribute to natural grasping manipulations in everyday life. However, in the case of robot systems, attempts to emulate humans’ dexterity are still limited by tactile sensory feedback. In this work, a soft optical lightguide is applied as an afferent nerve fiber in a tactile sensory system. A skin‐like soft silicone material is combined with a bristle friction model, which is capable of fast and easy fabrication. Due to this novel design, the soft sensor can provide not only normal force (up to 5 Newtons) but also lateral force information generated by stick‐slip processes. Through a static force test and slip motion test, its ability to measure normal forces and to detect stick‐slip events is demonstrated. Finally, using a robotic gripper, real‐time control applications are investigated where the sensor helps the gripper apply sufficient force to grasp objects without slipping.

Slowly-adapting type II afferents contribute to conscious touch sensation in humans: Evidence from single unit intraneural microstimulation.

Slowly‐adapting type II (SA‐II, Ruffini) mechanoreceptive afferents respond well to pressure and stretch, and are regularly encountered in human microneurography studies. Despite an understanding of SA‐II response properties, their role in touch perception remains unclear. Specific roles of different myelinated Aβ mechanoreceptive afferents in tactile perception have been revealed using single unit intraneural microstimulation (INMS), via microneurography, recording from and then electrically stimulating individual afferents. This method directly links single afferent artificial activation to perception, where INMS produces specific ‘quantal’ touch percepts associated with different mechanoreceptive afferent types. However, SA‐II afferent stimulation has been ambiguous, producing inconsistent, vague sensations, or no clear percept. We physiologically characterized hundreds of individual Aβ mechanoreceptive afferents in the glabrous hand skin and examined the subsequent percepts evoked by trains of low amplitude INMS current pulses (<10 μA). We present 18 SA‐II afferents where INMS resulted in a clear, electrically evoked sensation of large (∼36 mm2) diffuse pressure, which was projected precisely to their physiologically‐defined receptive field in the skin. This sensation was felt as natural, distinctive from other afferents, and showed no indications of multi‐afferent stimulation. Stimulus frequency modulated sensation intensity and even brief stimuli (4 pulses, 60 ms) were perceived. These results suggest that SA‐II afferents contribute to perceived tactile sensations, can signal this rapidly and precisely, and are relevant and important for computational models of touch sensation and artificial prosthetic feedback.Key points Slowly adapting type II mechanoreceptors (SA‐IIs) are primary sensory neurons in humans that respond to pressure and stretch applied to the skin.To date, no specific conscious correlate of touch has been linked to SA‐II activation.Using microneurography and intraneural microstimulation to stimulate single sensory neurons in human subjects, we find a specific sensation linked to the activation of single SA‐II afferents.This sensation of touch was reported as gentle pressure and subjects could detect this with a high degree of accuracy.Methods of artificial tactile sensory feedback and computational models of touch should include SA‐IIs as meaningful contributors to the conscious sensation of touch.

3. MOTOR CONTROL OF INDIVIDUAL DIGITS OF A ROBOTIC HAND USING ONLY SIGNALS RECORDED FROM THE PERIPHERAL NERVES

PURPOSE: Despite advances in artificial sensory feedback and EMG-based motor control, robotic hand “dexterity” remains elusive due to the inability to provide reliable individual digit motor control. We previously demonstrated functionally-relevant tactile and proprioceptive sensory feedback using fascicle-specific targeting of longitudinal intrafascicular electrodes (FAST-LIFE interfaces) implanted in the residual nerves of the amputated upper limb. Here we describe advances in motor control obtained by combining FAST-LIFE interfacing with peripheral nerve-specific motor control technology developed by our group. METHODS: Oversight by the UTSW IRB. 6 patient trials were performed, duration 3 - 15 months. Amputation level: 3 partial hand (FAST-LIFE interfaces in motor/sensory fascicles of ulnar nerve); 3 transradial (FAST-LIFE interfaces in motor/sensory fascicles of median + ulnar nerves). RESULTS: We demonstrated individual digit control of a robotic hand prosthesis using: 1) FAST-LIFE interfacing, 2) hardware for recording peripheral nerve signals, 3) machine learning decoding of motor intent, and 4) portable controllers for individual digit actuation. Details of decoding accuracy, task matching trials, and individual digit control will be discussed. The study culminated in a “take-home” trial. CONCLUSION: Individual digit control of a robotic hand prosthesis can be accomplished using only signals derived from FAST-LIFE implants placed in the residual nerves of the amputated upper limb. Our novel motor control strategy holds promise for robotic hand control in higher level amputations, where conventional EMG sensors are ineffective due to total absence of the forearm muscles.

Intracortical microstimulation of somatosensory cortex enables object identification through perceived sensations.

Advances in brain-machine interfaces have helped restore function and independence for individuals with sensorimotor deficits; however, providing efficient and effective sensory feedback remains challenging. Intracortical microstimulation (ICMS) of sensorimotor brain regions is a promising technique for providing bioinspired sensory feedback. In a human participant with chronically-implanted microelectrode arrays, we provided ICMS to the primary somatosensory cortex to generate tactile percepts in his hand. In a 3-choice object identification task, the participant identified virtual objects using tactile sensory feedback and no visual information. We evaluated three different stimulation paradigms, each with a different weighting of the grip force and its derivative, to explore the potential benefits of a more bioinspired stimulation strategy. In all paradigms, the participant's ability to identify the objects was above-chance, with object identification accuracy reaching 80% correct when using only sustained grip force feedback and 76.7% when using equal weighting of both sustained grip force and its derivative. These results demonstrate that bioinspired ICMS can provide sensory feedback that is functionally beneficial in sensorimotor tasks. Designing more efficient stimulation paradigms is important because it will allow us to 1) provide safer stimulation delivery methods that reduce overall injected charge without sacrificing function and 2) more effectively transmit sensory information to promote intuitive integration and usage by the human body.

Peak plantar pressure analysis using customized tactile sensory feedback system — A short report

Sensory neuropathy is prevalent in people affected by leprosy and diabetes. If neuropathy is left untreated it may lead to further impairments, which may be irreversible. Customized methods to identify and prevent further impairments in patients with sensory neuropathy are essential. The possibility of a sensory feedback system to identify pressure values on an anaesthetic foot was tested in this study. The feedback system to measure the peak plantar pressures was designed by integrating an electronic circuit to the data acquisition system. The sensor head of the Force Sensing Resistor (FSR’s) placed at various plantar pressure areas of the foot, determined the respective peak plantar pressures, based on sensing force. Feedback about the peak plantar pressure through the alerting terminals helps the user alter his gait and maintain the pressure within a set threshold limit. The system could also help the health staff to determine the patient’s peak plantar pressure and thus design customized therapeutic footwear.

An Experimental Protocol for Evaluating Pulse Width Modulation Ranges of Evoked Tactile Sensory Feedback in Amputees.

The objective of this study is to develop an experimental protocol to define the range of modulation for different sensory modalities elicited by transcutaneous electrical nerve stimulation (TENS) in amputees with evoked tactile sensation (ETS). Modulation ranges of sensory modalities, such as vibration, buzz, tingling etc., are essential for designing a coding strategy for incoming sensory information from prosthetic hands for each amputee. Here, the modulation ranges of different modalities in pulse width at fixed stimulus frequencies were evaluated. Four healthy subjects and three transradial amputee subjects were recruited to participate in this preliminary test. A single skin site in healthy subjects and five finger areas of the projected finger map (PFM) on the stump skin in amputee subjects were stimulated for evaluation. Then, a finger identification test was conducted to show the feasibility of this sensory coding strategy in one amputee subject. The sensitivity of different sensory modalities was also measured to quantify the minimum pulse width change that subject could distinguish. Results showed that vibration and buzz sensations had wider modulation ranges in pulse width for both healthy and amputee subjects at 20Hz and 50Hz of stimulation, respectively. The average accuracy of finger identification was 91.66% in the amputee subject. The minimum pulse width changes distinguishable for both vibration and buzz sensation were below 20 (us). Results indicated that the protocol of evaluating pulse width modulation ranges for different sensory modalities was effective, and the coding strategy could provide accurate finger-specific sensory information for amputees with ETS.Clinical Relevance- This protocol establishes a guideline for customizing the coding strategy of evoked tactile sensory feedback for each amputee.

Restoring the Sense of Touch: From "Sci-Fi Dream" to Reality.

A range of remarkable prostheses are now available to give function back to people who have had hands, arms, feet, or legs amputated, but for all their capabilities, these devices are missing a critical feature: a real sense of touch. Without it, a patient has no tactile sensory feedback on whether they have stepped off a curb or onto a misplaced child's toy, or are gripping a Styrofoam coffee cup or a toddler's hand too tightly or too loosely. Research projects today, however, are coming closer to restoring the sense of touch, which will help prostheses evolve from amazing tools to true replacement body parts.

A soft gripper with programmable effective length, tactile and curvature sensory feedback

Soft grippers based on fluidic elastomer actuators have the characteristics of gentle and adaptable grasping that is difficult to realize by rigid grippers. However, it remains challenging to implement a compact gripping device that has multiple bending configurations to exert appropriate force, and sensory capabilities to evaluate the grasping state. Here, we present a soft gripper with variable effective lengths (VELs) that is achieved by rapidly softening selective shape memory polymer sections (within 0.6 s) via a flexible heater. A vortex tube is used to jet cold airflow to accelerate the stiffening process (within 14 s). We show that the soft gripper can not only identify objects but also exert higher gripping force by setting appropriate length according to pneumatic-thermal hybrid actuation. We further propose a touch-reconfiguration-grasp strategy to showcase the synergy of VELs and sensory feedback. The gripper first touches the object under the fully softened state and evaluates the grasping condition based on the sensors’ feedback, then reconfigures the bending length and grasps the object until successful. We envision that soft grippers with sensing ability and reconfigurable grasping configurations would be promising for future applications in unconstructed environments.

The effect of lower leg sensory impulses on the force sense of knee extensor muscles in healthy adults: The accuracy of sense-of-force studies

BackgroundProducing the target force of a muscle group by using visual feedback and reproducing the same force fully blind are regarded as a common approach for quantifying the sense of force. Force sense error is considered to be the difference between the produced target force and reproduced force. The present study aimed to evaluate the effects of tactile sensory feedback in the lower leg on the perceived magnitude of force sense. Methods and materialsIn this cross-sectional study, 18 healthy men (mean age 24.31 ± 3.94 years) were selected based on a simple randomized method. First, the quantity of force sense error of the knee extensor muscle group was measured before and after manipulating the tactile inputs of the leg. Then, methods A, B, and C were applied to measure force sense errors. In addition, the tactile impulses were manipulated in methods B and C by placing a piece of thick foam between the distal portion of lower leg among the subjects and the dynamometer. The tactile inputs remained intact during method A. ResultsThe accuracy of the reproduced target force was significantly affected following the disturbance of tactile inputs in the lower leg in methods B and C, compared to method A (p < 0.05). ConclusionAltering tactile inputs in the lower leg can affect the force sense of the knee extensor muscles. The received somatosensory inputs across the lower leg can affect the whole process of force perception at this joint.

Grip control and motor coordination with implanted and surface electrodes while grasping with an osseointegrated prosthetic hand

BackgroundReplacement of a lost limb by an artificial substitute is not yet ideal. Resolution and coordination of motor control approximating that of a biological limb could dramatically improve the functionality of prosthetic devices, and thus reduce the gap towards a suitable limb replacement.MethodsIn this study, we investigated the control resolution and coordination exhibited by subjects with transhumeral amputation who were implanted with epimysial electrodes and an osseointegrated interface that provides bidirectional communication in addition to skeletal attachment (e-OPRA Implant System). We assessed control resolution and coordination in the context of routine and delicate grasping using the Pick and Lift and the Virtual Eggs Tests. Performance when utilizing implanted electrodes was compared with the standard-of-care technology for myoelectric prostheses, namely surface electrodes.ResultsResults showed that implanted electrodes provide superior controllability over the prosthetic terminal device compared to conventional surface electrodes. Significant improvements were found in the control of the grip force and its reliability during object transfer. However, these improvements failed to increase motor coordination, and surprisingly decreased the temporal correlation between grip and load forces observed with surface electrodes. We found that despite being more functional and reliable, prosthetic control via implanted electrodes still depended highly on visual feedback.ConclusionsOur findings indicate that incidental sensory feedback (visual, auditory, and osseoperceptive in this case) is insufficient for restoring natural grasp behavior in amputees, and support the idea that supplemental tactile sensory feedback is needed to learn and maintain the motor tasks internal model, which could ultimately restore natural grasp behavior in subjects using prosthetic hands.

Haptic Glove and Platform with Gestural Control For Neuromorphic Tactile Sensory Feedback In Medical Telepresence †.

Advancements in the study of the human sense of touch are fueling the field of haptics. This is paving the way for augmenting sensory perception during object palpation in tele-surgery and reproducing the sensed information through tactile feedback. Here, we present a novel tele-palpation apparatus that enables the user to detect nodules with various distinct stiffness buried in an ad-hoc polymeric phantom. The contact force measured by the platform was encoded using a neuromorphic model and reproduced on the index fingertip of a remote user through a haptic glove embedding a piezoelectric disk. We assessed the effectiveness of this feedback in allowing nodule identification under two experimental conditions of real-time telepresence: In Line of Sight (ILS), where the platform was placed in the visible range of a user; and the more demanding Not In Line of Sight (NILS), with the platform and the user being 50 km apart. We found that the entailed percentage of identification was higher for stiffer inclusions with respect to the softer ones (average of 74% within the duration of the task), in both telepresence conditions evaluated. These promising results call for further exploration of tactile augmentation technology for telepresence in medical interventions.

Automatic hand phantom map generation and detection using decomposition support vector machines

BackgroundThere is a need for providing sensory feedback for myoelectric prosthesis users. Providing tactile feedback can improve object manipulation abilities, enhance the perceptual embodiment of myoelectric prostheses and help reduce phantom limb pain. Many amputees have referred sensation from their missing hand on their residual limbs (phantom maps). This skin area can serve as a target for providing amputees with non-invasive tactile sensory feedback. One of the challenges of providing sensory feedback on the phantom map is to define the accurate boundary of each phantom digit because the phantom map distribution varies from person to person.MethodsIn this paper, automatic phantom map detection methods based on four decomposition support vector machine algorithms and three sampling methods are proposed, complemented by fuzzy logic and active learning strategies. The algorithms and methods are tested on two databases: the first one includes 400 generated phantom maps, whereby the phantom map generation algorithm was based on our observation of the phantom maps to ensure smooth phantom digit edges, variety, and representativeness. The second database includes five reported phantom map images and transformations thereof. The accuracy and training/ classification time of each algorithm using a dense stimulation array (with 100 times 100 actuators) and two coarse stimulation arrays (with 3 times 5 and 4 times 6 actuators) are presented and compared.ResultsBoth generated and reported phantom map images share the same trends. Majority-pooling sampling effectively increases the training size, albeit introducing some noise, and thus produces the smallest error rates among the three proposed sampling methods. For different decomposition architectures, one-vs-one reduces unclassified regions and in general has higher classification accuracy than the other architectures. By introducing fuzzy logic to bias the penalty parameter, the influence of pooling-induced noise is reduced. Moreover, active learning with different strategies was also tested and shown to improve the accuracy by introducing more representative training samples. Overall, dense arrays employing one-vs-one fuzzy support vector machines with majority-pooling sampling have the smallest average absolute error rate (8.78% for generated phantom maps and 11.5% for reported and transformed phantom map images). The detection accuracy of coarse arrays was found to be significantly lower than for dense array.ConclusionsThe results demonstrate the effectiveness of support vector machines using a dense array in detecting refined phantom map shapes, whereas coarse arrays are unsuitable for this task. We therefore propose a two-step approach, using first a non-wearable dense array to detect an accurate phantom map shape, then to apply a wearable coarse stimulation array customized according to the detection results. The proposed methodology can be used as a tool for helping haptic feedback designers and for tracking the evolvement of phantom maps.

Discrimination and Recognition of Phantom Finger Sensation Through Transcutaneous Electrical Nerve Stimulation.

Tactile sensory feedback would make a significant contribution to the state-of-the-art prosthetic hands for achieving dexterous manipulation over objects. Phantom finger sensation, also called referred sensation of lost fingers, can be noninvasively evoked by transcutaneous electrical nerve stimulation (TENS) of the phantom finger territories (PFTs) near the stump for upper-limb amputees. As such, intuitive sensations pertaining to lost fingers could be non-invasively generated. However, the encoding of stimulation parameters into tactile sensations that can be intuitively interpreted by the users remains a significant challenge. Further, how discriminative such artificial tactile sensation with TENS of the PFTs is still unknown. In this study, we systematically characterized the tactile discrimination across different phantom fingers on the stump skin by TENS among six subjects. Charge-balanced and biphasic stimulating current pulses were adopted. The pulse amplitude (PA), the pulse frequency (PF) and the pulse width (PW) were modulated to evaluate the detection threshold, perceived touch intensity, and the just-noticeable difference (JND) of the phantom finger sensation. Particularly, the recognition of phantom fingers under simultaneous stimulation was assessed. The psychophysical experiments revealed that subjects could discern fine variations of stimuli with comfortable sensation of phantom fingers including D1 (phantom thumb), D2 (phantom index finger), D3 (Phantom middle finger), and D5 (Phantom pinky finger). With respect to PA, PF, and PW modulations, the detection thresholds across the four phantom fingers were achieved by the method of constant stimuli based on a two-alternative forced-choice (2AFC) paradigm. For each modulation, the perceived intensity, which was indexed by skin indentations on the contralateral intact finger pulp, reinforced gradually with enhancing stimuli within lower-intensity range. Particularly, the curve of the indentation depth vs. PF almost reached a plateau with PF more than 200 Hz. Moreover, the performance of phantom finger recognition deteriorated with the increasing number of phantom fingers under simultaneous TENS. For one, two and four stimulating channels, the corresponding recognition rate of an individual PFT were respective 85.83, 67.67, and 46.44%. The results of the present work would provide direct guidelines regarding the optimization of stimulating strategies to deliver artificial tactile sensation by TENS for clinical applications.

A psychophysical investigation on vibrotactile sensing for transradial prosthesis users

AbstractThe absence of tactile sensory feedback in transradial prosthetic hands is one of the major contributing factors for these devices to be rejected by users. This paper reports human psychophysical response to vibrotactile sensations in discriminating surface textures, as a possible non-invasive method to supplement sensory feedback for prosthetic hand users. The vibrotactile sensations were supplied by a specially fabricated actuator that vibrates according to signals obtained by a prosthetic finger when sliding across textured surfaces. Participants were provided with four different types of vibration patterns, randomly repeated for five times and were required to state which surface textures that the vibration patterns represent. A Chi-square test statistical procedure was designed to evaluate the relationships between these two categorical variables. The investigation which comprises of 300 samples has shown a statistically significant relationship between the vibration patterns and the surface ...

A 3D Computational Model of Transcutaneous Electrical Nerve Stimulation for Estimating Aβ Tactile Nerve Fiber Excitability.

Tactile sensory feedback plays an important role in our daily life. Transcutaneous electrical nerve stimulation (TENS) is widely accepted to produce artificial tactile sensation. To explore the underlying mechanism of tactile sensation under TENS, this paper presented a novel 3D TENS computational model including an active Aβ tactile nerve fiber (TNF) model and a forearm finite element model with the fine-layered skin structure. The conduction velocity vs. fiber diameter and strength-duration relationships in this combined TENS model matched well with experimental data. Based on this validated TENS model, threshold current variation were further investigated under different stimulating electrode sizes with varied fiber diameters. The computational results showed that the threshold current intensity increased with electrode size, and larger nerve fibers were recruited at lower current intensities. These results were comparable to our psychophysical experimental data from six healthy subjects. This novel 3D TENS model would further guide the floorplan of the surface electrodes, and the stimulating paradigms for tactile sensory feedback.