Electrotactile Feedback Research Articles

Shock Me The Way: Directional Electrotactile Feedback under the Smartwatch as a Navigation Aid for Cyclists

Cycling navigation is a complex and stressful task as the cyclist needs to focus simultaneously on the navigation, the road, and other road users. We propose directional electrotactile feedback at the wrist to reduce the auditory and visual load during navigation-aided cycling. We designed a custom electrotactile grid with 9 electrodes that is clipped under a smartwatch. In a preliminary study we identified suitable calibration settings and gained first insights about a suitable electrode layout. In a subsequent laboratory study we showed that a direction can be encoded with a mean error of 19.28\,° (σ = 42.77°) by combining 2 adjacent electrodes. Additionally, by interpolating with 3 electrodes a direction can be conveyed with a similar mean error of 22.54° (σ = 43.57°). We evaluated our concept of directional electrotactile feedback for cyclists in an outdoor study, in which 98.8% of all junctions were taken correctly by eight study participants. Only one participant deviated substantially from the optimal path, but was successfully navigated back to the original route by our system.

Psychometric evaluation of high-resolution electrotactile interface for conveying 3D spatial information

This study presents a detailed psychometric evaluation of a novel high-resolution electrotactile interface, which is developed to provide users with 3D spatial information and facilitate enhanced interaction with a Supernumerary Robotic Limb (SRL). The research introduces a novel electrotactile system that employs a multi-pad electrode configuration on the thigh, aimed at delivering intuitive feedback to users about the position of the SRL in a three-dimensional space. The interface's effectiveness was assessed through a series of psychometric tests, including static spatial discrimination, target-reaching with spatial feedback, frequency discrimination, and combined spatial/frequency modulation. The key findings demonstrate that participants could differentiate between 30 electrode pads with an average success rate of 62.7% when they were activated statically, while in the dynamic target-reaching task, the success rate increased to 88.1%. Frequency discrimination tests further revealed that four frequency levels could be distinguished with 86.0% success rate in single-pad feedback while the performance decreased to 74.3% in multi-pad distributed feedback. Finaly, in the closed-loop test with mixed spatial and frequency modulation, participants achieved an overall success rate of 78.8% in target reaching across 10 × 4 discrete 2D space. These results highlight the interface’s capability to transmit high-resolution spatial information through electrotactile feedback, offering a foundation for future applications in tactile-based navigation and control systems.

Proportional sway-based electrotactile feedback improves lateral standing balance.

Plantar cutaneous augmentation is a promising approach in balance rehabilitation by enhancing motion-dependent sensory feedback. The effect of plantar cutaneous augmentation on balance has been mainly investigated in its passive form (e.g., textured insole) or on lower-limb amputees. In this study, we tested the effect of plantar cutaneous augmentation on balance in its active form (i.e., electrical stimulation) for individuals with intact limbs. Ten healthy subjects participated in the study and were instructed to maintain their balance as long as possible on the balance board, with or without electrotactile feedback evoked on the medial side of the heel, synched with the lateral board sway. Electrotactile feedback was given in two different modes: 1) Discrete-mode E-stim as the stimulation on/off by a predefined threshold of lateral board sway and 2) Proportional-mode E-stim as the stimulation frequency proportional to the amount of lateral board sway. All subjects were distracted from the balancing task by the n-back counting task, to test subjects' balancing capability with minimal cognitive involvement. Proportional-mode E-stim, along with the n-back counting task, increased the balance time from 1.86 ± 0.03 s to 1.98 ± 0.04 s (p = 0.010). However, discrete-mode E-stim did not change the balance time (p = 0.669). Proportional-mode E-stim also increased the time duration per each swayed state (p = 0.035) while discrete-mode E-stim did not (p = 0.053). These results suggest that proportional-mode E-stim is more effective than discrete-mode E-stim on improving standing balance. It is perhaps because the proportional electrotactile feedback better mimics the natural tactile sensation of foot pressure than its discrete counterpart.

Location-based electrotactile feedback localizes hitting point in virtual-reality table tennis game.

Learning new motor skills is often challenged by sensory mismatches. For reliable sensory information, people have actively employed sensory intervention methods. Visual assistance is the most popular method to provide sensory information, which is equivalent to the knowledge of performance (KP) in motor tasks. However, its efficacy is questionable because of visual-proprioceptive mismatch as well as heavy intrinsic visual and cognitive engagement in motor tasks. Electrotactile intervention is a promising technique to address the current limitations, as it provides KP using tactile feedback that has a close neurophysiological association with proprioception. To test its efficacy, we compared the effects of visual and electrotactile assistance on hitting point localization of the table-tennis racket during virtual-reality table-tennis game. Experimental results suggest that location-based electrotactile feedback outperforms visual assistance in localizing the hitting point on a table-tennis racket during virtual-reality table-tennis game. Our study showed the potential of electrotactile intervention for improving the efficacy of new motor skill training.

Fusion of dual modalities of non-invasive sensory feedback for object profiling with prosthetic hands.

Either non-invasive somatotopic or substitute sensory feedback is capable of conveying a single modality of sensory information from prosthetic hands to amputees. However, the neurocognitive ability of amputees to integrate multi-modality sensory information for functional discrimination is unclear. The purpose of this study was to assess the fusion of non-invasive somatotopic tactile and substitute aperture feedbacks for profile perception of multiple physical features during grasping objects. Two left transradial amputees with somatotopic evoked tactile sensation (ETS) of five fingers participated in the study. The tactile information of prosthetic hand was provided to amputees by the ETS feedback elicited on the stump projected finger map. Hand aperture information was conveyed to amputees with substitute electrotactile stimulation on the forearm or upper arm. Two types of sensory feedback were integrated to a commercial prosthetic hand. The efficacy of somatotopic ETS feedback on object length identification task was assessed with or without substitute aperture stimulation. The object size identification task was utilized to assess how ETS stimulation at the stump may affect aperture perception with stimulation on the ipsilateral upper arm or forearm. Finally, the task of identifying combined length and size was conducted to evaluate the ability of amputees to integrate the dual modalities of sensory feedback for perceiving profile features. The study revealed that amputee subjects can effectively integrate the ETS feedback with electrotactile substitutive feedback for object profile discrimination. Specifically, ETS was robust to provide object length information with electrotactile stimulation at either the forearm or upper arm. However, electrotactile stimulation at the upper arm for aperture perception was less susceptible to the interference of ETS stimulation than at the forearm. Amputee subjects are able to combine somatotopic ETS and aperture feedbacks for identifying multi-dimensional features in object profiling. The two sensory streams of information can be fused effectively without mutual interference for functional discrimination.

Exploring Perceptual Intensity Properties Using Electrotactile Stimulation on Fingertips.

Understanding electrotactile parametric properties is a crucial milestone in achieving intuitive haptics. Perceptual intensity is a primary property, but its exploration remains challenging due to subjectivity. To address this problem, this study conducted two experiments on fingertips and proposed two metrics based on significant findings. Experiment 1 found a significant linear relationship (R 2 = 0.981) between pulse amplitude (PA) and pulse width (PW) in the logarithmic plane, and proposed a metric of parameter intensity (PI) to estimate the intensity of parameters. In Experiment 2, subjective intensity (SI) was defined and measured using a scale of 0 to 10. A metric model of SI (SI model) was derived based on the linear relationship (R 0.78) between PI and measured SI. A calibration method was proposed and its prediction accuracy has been verified. An average RMSE of 11.2 % indicated an accuracy close to the subjective judgment error of 8.7 %. Results are consistent across subjects and four different electrode-skin conditions (ESC). The findings of this study provide theoretical support for SI prediction and regulation, which is significant for electrotactile feedback.

The rubber hand illusion evaluated using different stimulation modalities.

Tactile feedback plays a vital role in inducing ownership and improving motor control of prosthetic hands. However, commercially available prosthetic hands typically do not provide tactile feedback and because of that the prosthetic user must rely on visual input to adjust the grip. The classical rubber hand illusion (RHI) where a brush is stroking the rubber hand, and the user's hidden hand synchronously can induce ownership of a rubber hand. In the classic RHI the stimulation is modality-matched, meaning that the stimulus on the real hand matches the stimulus on the rubber hand. The RHI has also been used in previous studies with a prosthetic hand as the "rubber hand," suggesting that a hand prosthesis can be incorporated within the amputee's body scheme. Interestingly, previous studies have shown that stimulation with a mismatched modality, where the rubber hand was brushed, and vibrations were felt on the hidden hand also induced the RHI. The aim of this study was to compare how well mechanotactile, vibrotactile, and electrotactile feedback induced the RHI in able-bodied participants and forearm amputees. 27 participants with intact hands and three transradial amputees took part in a modified RHI experiment. The rubber hand was stroked with a brush, and the participant's hidden hand/residual limb received stimulation with either brush stroking, electricity, pressure, or vibration. The three latter stimulations were modality mismatched with regard to the brushstroke. Participants were tested for ten different combinations (stimulation blocks) where the stimulations were applied on the volar (glabrous skin), and dorsal (hairy skin) sides of the hand. Outcome was assessed using two standard tests (questionnaire and proprioceptive drift). All types of stimulation induced RHI but electrical and vibration stimulation induced a stronger RHI than pressure. After completing more stimulation blocks, the proprioceptive drift test showed that the difference between pre- and post-test was reduced. This indicates that the illusion was drifting toward the rubber hand further into the session.

Characterization of perception by transcutaneous electrical Stimulation in terms of tingling intensity and temporal dynamics.

Electrotactile feedback is a cost-effective and versatile method to provide new information or to augment intrinsic tactile feedback. As tactile feedback provides critical information for human-environment interaction, electrotactile feedback, accordingly, has many purposes to improve the quality of human-environment interaction in both direct and remote settings. However, electrotactile feedback overlays tingling sensation on top of the natural tactile feedback. To better characterize electrotactile feedback and understand the origin of the tingling sensation, a need arises to characterize the human perception of electrotactile feedback qualitatively and quantitatively, while varying the key stimulation parameters, namely amplitude and frequency. This study consists of two experiments. In the first experiment, the voltage for each subject was characterized by setting perception and discomfort thresholds. In the second experiment, subjects received electrical stimulation in 9 different combinations of voltages and frequencies. On delivering stimulation with each parameter combination, subjects reported their perception in two comparative scales-pressure vs. tingling and constant vs. pulsing. Subjects also reported the location of perception for stimulation with every parameter combination. More tingling and less pressure was reported as frequency increased, while the tingling-pressure percept was not affected by the amplitude change. Additionally, less pulsing and more constant was reported as frequency increased, while the pulsing-constant percept was not affected by the amplitude change. Concurrently, the normalized level of voltage thresholds was decreased as frequency increased. Dependency of tingling-pressure percept on stimulation frequency suggests that incongruency between the stimulation frequency and the natural firing rate of the sensory neuron would be an important factor of the tingling sensation. This study is a steppingstone to further demystify the origin of the tingling percept caused by electrical stimulation, thus broadening the use of transcutaneous electrical stimulation as a way of providing tactile cue or augmentation.

The impact of walking on the perception of multichannel electrotactile stimulation in individuals with lower-limb amputation and able-bodied participants

BackgroundOne of the drawbacks of lower-limb prostheses is that they do not provide explicit somatosensory feedback to their users. Electrotactile stimulation is an attractive technology to restore such feedback because it enables compact solutions with multiple stimulation points. This allows stimulating a larger skin area to provide more information concurrently and modulate parameters spatially as well as in amplitude. However, for effective use, electrotactile stimulation needs to be calibrated and it would be convenient to perform this procedure while the subject is seated. However, amplitude and spatial perception can be affected by motion and/or physical coupling between the residual limb and the socket. In the present study, we therefore evaluated and compared the psychometric properties of multichannel electrotactile stimulation applied to the thigh/residual limb during sitting versus walking.MethodsThe comprehensive assessment included the measurement of the sensation and discomfort thresholds (ST & DT), just noticeable difference (JND), number of distinct intervals (NDI), two-point discrimination threshold (2PD), and spatial discrimination performance (SD). The experiment involved 11 able-bodied participants (4 females and 7 males; 29.2 ± 3.8 years), 3 participants with transtibial amputation, and 3 participants with transfemoral amputation.ResultsIn able-bodied participants, the results were consistent for all the measured parameters, and they indicated that both amplitude and spatial perception became worse during walking. More specifically, ST and DT increased significantly during walking vs. sitting (2.90 ± 0.82 mA vs. 2.00 ± 0.52 mA; p < 0.001 for ST and 7.74 ± 0.84 mA vs. 7.21 ± 1.30 mA; p < 0.05 for DT) and likewise for the JND (22.47 ± 12.21% vs. 11.82 ± 5.07%; p < 0.01), while the NDI became lower (6.46 ± 3.47 vs. 11.27 ± 5.18 intervals; p < 0.01). Regarding spatial perception, 2PD was higher during walking (69.78 ± 17.66 mm vs. 57.85 ± 14.87 mm; p < 0.001), while the performance of SD was significantly lower (56.70 ± 10.02% vs. 64.55 ± 9.44%; p < 0.01). For participants with lower-limb amputation, the ST, DT, and performance in the SD assessment followed the trends observed in the able-bodied population. The results for 2PD and JND were however different and subject-specific.ConclusionThe conducted evaluation demonstrates that electrotactile feedback should be calibrated in the conditions in which it will be used (e.g., during walking). The calibration during sitting, while more convenient, might lead to an overly optimistic (or in some cases pessimistic) estimate of sensitivity. In addition, the results underline that calibration is particularly important in people affected by lower-limb loss to capture the substantial variability in the conditions of the residual limb and prosthesis setup. These insights are important for the implementation of artificial sensory feedback in lower-limb prosthetics applications.

Encoding force modulation in two electrotactile feedback parameters strengthens sensory integration according to maximum likelihood estimation

Bidirectional human–machine interfaces involve commands from the central nervous system to an external device and feedback characterizing device state. Such feedback may be elicited by electrical stimulation of somatosensory nerves, where a task-relevant variable is encoded in stimulation amplitude or frequency. Recently, concurrent modulation in amplitude and frequency (multimodal encoding) was proposed. We hypothesized that feedback with multimodal encoding may effectively be processed by the central nervous system as two independent inputs encoded in amplitude and frequency, respectively, thereby increasing state estimate quality in accordance with maximum-likelihood estimation. Using an adaptation paradigm, we tested this hypothesis during a grasp force matching task where subjects received electrotactile feedback encoding instantaneous force in amplitude, frequency, or both, in addition to their natural force feedback. The results showed that adaptations in grasp force with multimodal encoding could be accurately predicted as the integration of three independent inputs according to maximum-likelihood estimation: amplitude modulated electrotactile feedback, frequency modulated electrotactile feedback, and natural force feedback (r2 = 0.73). These findings show that multimodal electrotactile feedback carries an intrinsic advantage for state estimation accuracy with respect to single-variable modulation and suggest that this scheme should be the preferred strategy for bidirectional human–machine interfaces with electrotactile feedback.

Design, evaluation and calibration of wearable electrotactile interfaces for enhancing contact information in virtual reality

Electrotactile feedback is a convenient tactile rendering method thanks to reduced form factor and power consumption. Yet, its usage in immersive virtual reality has been scarcely addressed. This paper explores how electrotactile feedback could be used to enhance contact information for mid-air interactions in virtual reality. We propose an electrotactile rendering method which modulates the perceived intensity of the electrotactile stimuli according to the interpenetration distance between the user’s finger and the virtual surface. In a first user study (N=21), we assessed the performance of our method against visual interpenetration feedback and no-feedback. Contact precision and accuracy were significantly improved when using interpenetration feedback. The results also showed that the calibration of the electrotactile stimuli was key, which motivated a second study exploring how the calibration procedure could be improved. In a second study (N=16), we compared two calibration techniques: a non-VR keyboard and a VR direct interaction method. While the two methods provided comparable usability and calibration accuracy, the VR method was significantly faster. These results pave the way for the usage of electrotactile feedback as an efficient alternative to visual feedback for enhancing contact information in virtual reality.

Prosthetic Elbow Flexion and Extension Sense rebuilt by Electrotactile Feedback: a Preliminary Study

The elbow position and movement (PM) feedback can help amputees control the prosthetic limbs more flexibly. This study attempts to explore whether electrotactile stimulation can help amputees identify the elbow PM information of prosthesis, due to valuable potential of electrotactile stimulation. This study designed an encoding scheme by relating the elbow PM information with amplitudes, and it tested the scheme on four able-bodied subjects and two transhumeral amputees. After two stimulation positions on the upper limb were determined using sensory sensitivity experiment, four sets of amplitudes (Am, An) were encoded four positions of prosthetic elbow (0°, 45°, 90°, and 135°) and changes in sets of amplitudes were encoded flexion and extension (FE) movements of prosthetic elbow. All subjects were required to identify the prosthetic elbow PM during the experiment, and the success rate and discrimination reaction time were recorded. The average success rates of the position and movement experiments among the four subjects were 76.25% and 91.17% respectively. For the two transhumeral amputees, the position feedback success rates were 86.38% and 75%, respectively, and the movement feedback success rates were 80.5% and 75%, respectively. These results indicate that subjects can learn the mapping relationship of this sensory feedback after training. This method potentially in future provides amputees with PM sensory information of elbow FE during the actual control of prosthetic elbows.

Mathematical Model of Fingertip Skin Under Constant-Current Electrotactile Stimulation.

Due to low energy consumption and fast response, electrotactile feedback has shown great potential in human-machine interaction. However, regulating electrotactile perception remains challenging because of the high variability of electrode-skin impedance. Electrode-skin modelling is a common solution, but current researches are still facing many problems such as non-linearity. This paper focuses on voltage response modelling based on data-driven analysis. Two experiments targeting fingertips have been conducted. Significant correlations between pulse amplitude ( PA), pulse width ( PW) and peak voltage ( Vpeak) ( 0.99) have been found. A mathematical model of fingertip skin is then derived, which enables a precision fitting of the voltage response (RMSE=0.9 %). Finally, two calibration methods are proposed for peak voltage prediction. The accuracy (RMSE=2.5 %) is also verified under different electrode-skin conditions. The results of this paper are expected to provide novel theoretical support for precise regulation of fingertip electrotactile perception.

A TENS Based System for 2-Dimensional Balance Biofeedback Under Muscle Fatigue Condition

Many balance assist or training systems have been developed to improve postural control, however these have limitations such as being bulky or unable to provide 2-dimensional feedback. Furthermore, efficiency of the commonly used vibro-tactile feedback modality can be reduced due to muscle fatigue. Therefore, we suggest a transcutaneous electrical nerve stimulation (TENS) based electro-tactile biofeedback system to provide efficient balance biofeedback even under muscle fatigue condition. A feedback scheme based on Stevens’ power law is devised to provide 2-dimensional feedback using only four electrodes attached to the user’s leg. A pilot test involving the tracking of directions indicated by stimuli was done to select the algorithm appropriate for use in the directional perception test and the balance study. The perception, in 8 directions, of electro-tactile cues delivered using the developed scheme is compared with that of vibro-tactile cues under both normal and fatigued conditions. In addition, we have done standing balance experiments to verify the effectiveness of the developed balance biofeedback scheme. 20 healthy participants took part in these experiments that were conducted under two conditions. The perception results show that under the fatigued condition, the electro-tactile modality is more perceptible than the vibro-tactile modality. Results of the balance biofeedback experiment with no feedback, continuous stimulation with and without dead-zone and directional feedback conditions show that directional electro-tactile feedback helped the most in improving the users’ balance under normal and fatigued conditions. These promising results pave the way for future studies on the applications of this scheme for balance rehabilitation.

Closed-Loop Control of a Multifunctional Myoelectric Prosthesis With Full-State Anatomically Congruent Electrotactile Feedback.

State-of-the-art myoelectric hand prostheses provide multi-functional control but lack somatosensory feedback. To accommodate the full functionality of a dexterous prosthesis, the artificial sensory feedback needs to convey several degrees of freedom (DoF) simultaneously. However, this is a challenge with current methods as they are characterized by a low information bandwidth. In this study, we leverage the flexibility of a recently developed system for simultaneous electrotactile stimulation and electromyography (EMG) recording to present the first solution for closed-loop myoelectric control of a multifunctional prosthesis with full-state anatomically congruent electrotactile feedback. The novel feedback scheme (coupled encoding) conveyed proprioceptive (hand aperture, wrist rotation) and exteroceptive information (grasping force). The coupled encoding was compared to the conventional approach (sectorized encoding) and incidental feedback in 10 non-disabled and one amputee participant who used the system to perform a functional task. The results showed that both feedback approaches increased the accuracy of position control compared to incidental feedback. However, the feedback increased completion time, and it did not significantly improve grasping force control. Importantly, the performance of the coupled feedback was not significantly different compared to the conventional scheme, despite the latter being easier to learn during training. Overall, the results indicate that the developed feedback can improve prosthesis control across multiple DoFs but they also highlight the subjects' ability to exploit minimal incidental information. Importantly, the current setup is the first to convey three feedback variables simultaneously using electrotactile stimulation while providing multi-DoF myoelectric control with all hardware components mounted on the same forearm.

Task-Dependent Adaptations in Closed-Loop Motor Control Based on Electrotactile Feedback

Humans systematically adapt their strategies for closed-loop control based on visual feedback according to the dynamics of the system. Tactile feedback is a key element in many human–machine interfaces, but it is not known if and how well human control adapts to changes in system dynamics when information about the system state is provided using this type of feedback. In this study, 11 participants tracked a pseudorandom trajectory with a virtual, position- or velocity-controlled plant using a joystick. Visual or electrotactile feedback provided the instantaneous error between the target and generated trajectory. Frequency-domain system identification indicated that human control adapted in similar ways to the different control modes (i.e., position/velocity control) for both feedback modalities. For the plant dynamics modeled as gain and integrator, the human controller behaved as a low-pass filter and gain, respectively (under the assumption of quasi-linear behavior). However, while tracking quality was largely similar for both control modes with visual feedback, velocity control enabled substantially worse control with electrotactile feedback compared to position control. Furthermore, for both control modes, the crossover frequency of open-loop transfer functions was lower for electrotactile feedback (0.9 and 1.1 rad/s) than for visual feedback (1.5 and 1.7 rad/s) indicating limited control bandwidth. To summarize, closed-loop control based on electrotactile feedback enables natural adaptations in human control strategy, which is encouraging for tactile feedback-controlled human–machine interfaces, but the lower control bandwidth and lower tracking quality with velocity control may impose functional limitations.

EEG guided electrical stimulation parameters generation from texture force profiles

Objective. Our aim is to enhance sensory perception and spatial presence in artificial interfaces guided by EEG. This is done by developing a closed-loop electro-tactile system guided by EEG that adaptively update the electrical stimulation parameters to achieve EEG responses similar to the EEG responses generated from touching textured surface. Approach. In this work, we introduce a model that defines the relationship between the contact force profiles and the electrical stimulation parameters. This is done by using the EEG and force data collected from two experiments. The first was conducted by moving a set of textured surfaces against the subjects’ fingertip, while collecting both EEG and force data. Whereas the second was carried out by applying a set of different pulse and amplitude modulated electrical stimuli to the subjects’ index finger while recording EEG. Main results. We were able to develop a model which could generate electrical stimulation parameters corresponding to different textured surfaces. We showed by offline testing and validation analysis that the average error between the EEG generated from the estimated electrical stimulation parameters and the actual EEG generated from touching textured surfaces is around 7%. Significance. Haptic feedback plays a vital role in our daily life, as it allows us to become aware of our environment. Even though a number of methods have been developed to measure perception of spatial presence and provide sensory feedback in virtual reality environments, there is currently no closed-loop control of sensory stimulation. The proposed model provides an initial step towards developing a closed loop electro-tactile haptic feedback model that delivers more realistic touch sensation through electrical stimulation.

Action-Specific Perception &amp; Performance on a Fitts's Law Task in Virtual Reality: The Role of Haptic Feedback

While user's perception and performance are predominantly examined independently in virtual reality, the Action-Specific Perception (ASP) theory postulates that the performance of an individual on a task modulates this individual's spatial and time perception pertinent to the task's components and procedures. This paper examines the association between performance and perception and the potential effects that tactile feedback modalities could generate. This paper reports a user study (N=24), in which participants performed a standardized Fitts's law target acquisition task by using three feedback modalities: visual, visuo-electrotactile, and visuo-vibrotactile. The users completed 3 Target Sizes × 2 Distances × 3 feedback modalities = 18 trials. The size perception, distance perception, and (movement) time perception were assessed at the end of each trial. Performance-wise, the results showed that electrotactile feedback facilitates a significantly better accuracy compared to vibrotactile and visual feedback, while vibrotactile provided the worst accuracy. Electrotactile and visual feedback enabled a comparable reaction time, while the vibrotactile offered a substantially slower reaction time than visual feedback. Although amongst feedback types the pattern of differences in perceptual aspects were comparable to performance differences, none of them was statistically significant. However, performance indeed modulated perception. Significant action-specific effects on spatial and time perception were detected. Changes in accuracy modulate both size perception and time perception, while changes in movement speed modulate distance perception. Also, the index of difficulty was found to modulate all three perceptual aspects. However, individual differences appear to affect the magnitude of action-specific effects. These outcomes highlighted the importance of haptic feedback on performance, and importantly the significance of action-specific effects on spatial and time perception in VR, which should be considered in future VR studies.

Orientation of tactile attention on the surface of the tongue.

The tongue is an incredibly complex sensory organ, yet little is known about its tactile capacities compared to the hands. In particular, the tongue receives almost no visual input during development and so may be calibrated differently compared to other tactile senses for spatial tasks. Using a cueing task, via an electro-tactile display, we examined how a tactile cue (to the tongue) or an auditory cue can affect the orientation of attention to electro-tactile targets presented to one of four regions on the tongue. We observed that response accuracy was generally low for the same modality condition, especially at the back of the tongue. This implies that spatial localization ability is diminished either because the tongue is less calibrated by the visual modality or because of its position and orientation inside the body. However, when cues were provided cross-modally, target identification at the back of the tongue seemed to improve. Our findings suggest that, while the brain relies on a general mechanism for spatial (and tactile) attention, the surface of the tongue may not have clear access to these representations of space when solely provided via electro-tactile feedback but can be directed by other sensory modalities. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Combined spatial and frequency encoding for electrotactile feedback of myoelectric signals

Electrotactile stimulation has been commonly used in human–machine interfaces to provide feedback to the user, thereby closing the control loop and improving performance. The encoding approach, which defines the mapping of the feedback information into stimulation profiles, is a critical component of an electrotactile interface. Ideally, the encoding will provide a high-fidelity representation of the feedback variable while being easy to perceive and interpret by the subject. In the present study, we performed a closed-loop experiment wherein discrete and continuous coding schemes are combined to exploit the benefits of both techniques. Subjects performed a muscle activation-matching task relying solely on electrotactile feedback representing the generated myoelectric signal (EMG). In particular, we investigated the performance of two different coding schemes (spatial and spatial combined with frequency) at two feedback resolutions (low: 3 and high: 5 intervals). In both schemes, the stimulation electrodes were placed circumferentially around the upper arm. The magnitude of the normalized EMG was divided into intervals, and each electrode was associated with one interval. When the generated EMG entered one of the intervals, the associated electrode started stimulating. In the combined encoding, the additional frequency modulation of the active electrode also indicated the momentary magnitude of the signal within the interval. The results showed that combined coding decreased the undershooting rate, variability and absolute deviation when the resolution was low but not when the resolution was high, where it actually worsened the performance. This demonstrates that combined coding can improve the effectiveness of EMG feedback, but that this effect is limited by the intrinsic variability of myoelectric control. Our findings, therefore, provide important insights as well as elucidate limitations of the information encoding methods when using electrotactile stimulation to convey a feedback signal characterized by high variability (EMG biofeedback).