Investigating Electrotactile Feedback on The Hand

Electrotactile feedback can be used as a novel method to evoke different sensations on the skin. However, there is a lack of research exploring electrotactile feedback on the palm. This paper presents two experiments that in- vestigate the effects of manipulating pulse width, amplitude and frequency of electrical stimulation on perceived sensations (urgency, annoyance, valence and arousal) on the palm. In the first study, we manipulated pulse width and frequency. The results showed that both parameters have a significant effect on the perceived sensations, except for frequency not having an effect on valence. Also, frequencies of 30Hz and above did not influence the perceived sensations. In the second study, we manipulated amplitude and frequency. The results showed that both parameters have a significant effect on perceived sensations, especially for frequencies lower than 30Hz. From both experiments, the increment of pulse width and amplitude led to a higher rating for urgency, annoyance and arousal. These results gives us a better understanding of the parameter space of electrotactile feedback to enable designers to create effective electrotactile feedback

Investigating Electrotactile Feedback on The Hand

Electrotactile feedback can be used as a novel method to evoke different sensations on the skin. However, there is a lack of research exploring electrotactile feedback on the palm. This paper presents two experiments that in- vestigate the effects of manipulating pulse width, amplitude and frequency of electrical stimulation on perceived sensations (urgency, annoyance, valence and arousal) on the palm. In the first study, we manipulated pulse width and frequency. The results showed that both parameters have a significant effect on the perceived sensations, except for frequency not having an effect on valence. Also, frequencies of 30Hz and above did not influence the perceived sensations. In the second study, we manipulated amplitude and frequency. The results showed that both parameters have a significant effect on perceived sensations, especially for frequencies lower than 30Hz. From both experiments, the increment of pulse width and amplitude led to a higher rating for urgency, annoyance and arousal. These results gives us a better understanding of the parameter space of electrotactile feedback to enable designers to create effective electrotactile feedback

Tongue-placed tactile biofeedback suppresses the deleterious effects of muscle fatigue on joint position sense at the ankle

Whereas the acuity of the position sense at the ankle can be disturbed by muscle fatigue, it recently also has been shown to be improved, under normal ankle neuromuscular state, through the use of an artificial tongue-placed tactile biofeedback. The underlying principle of this biofeedback consisted of supplying individuals with supplementary information about the position of their matching ankle position relative to their reference ankle position through electrotactile stimulation of the tongue. Within this context, the purpose of the present experiment was to investigate whether this biofeedback could mitigate the deleterious effect of muscle fatigue on joint position sense at the ankle. To address this objective, sixteen young healthy university students were asked to perform an active ankle-matching task in two conditions of No-fatigue and Fatigue of the ankle muscles and two conditions of No-biofeedback and Biofeedback. Measures of the overall accuracy and the variability of the positioning were determined using the absolute error and the variable error, respectively. Results showed that the availability of the biofeedback allowed the subjects to suppress the deleterious effects of muscle fatigue on joint position sense at the ankle. In the context of sensory re-weighting process, these findings suggested that the central nervous system was able to integrate and increase the relative contribution of the artificial tongue-placed tactile biofeedback to compensate for a proprioceptive degradation at the ankle

The Impact of Stimulation Intensity on Spatial Discrimination with Multi-Pad Finger Electrode

Multi-pad electrotactile stimulation can be used to provide tactile feedback in different applications. The electrotactile interface needs to be calibrated before each use, which entails adjusting the intensity to obtain clear sensations while allowing the subjects to differentiate between active pads. The present study investigated how the stimulation intensity affects the localization of sensations using a multi-pad electrode placed on a fingertip and proximal phalange. First, the sensation, localization, smearing and discomfort thresholds were determined in 11 subjects. Then, the same subjects performed a spatial discrimination test across a range of stimulation intensities. The results have shown that all thresholds were significantly different, while there was no difference in the threshold values between the pads and phalanges. Despite the subjective feeling of spreading of sensations, the success rates in spatial discrimination were not significantly different across the tested stimulation intensities. However, the performance was better for distal compared to proximal phalange. Presented results indicate that spatial discrimination is robust to changes in the stimulation intensity. Considering the lack of significant difference in the thresholds between the pads, these results imply that more coarse adjustment of stimulation amplitude (faster calibration) might be enough for practical applications of a multi-pad electrotactile interface.This research was funded by the TACTILITY project, which has received funding by European Union’s Horizon 2020 framework programme for research and innovation H2020-ICT 2018-2020/H2020-ICT-2018-3 under grant agreement no. 856718

Electrotactile feedback applications for hand and arm interactions: A systematic review, meta-analysis, and future directions

Haptic feedback is critical in a broad range of human-machine/computer-interaction applications. However, the high cost and low portability/wearability of haptic devices remain unresolved issues, severely limiting the adoption of this otherwise promising technology. Electrotactile interfaces have the advantage of being more portable and wearable due to their reduced actuators' size, as well as their lower power consumption and manufacturing cost. The applications of electrotactile feedback have been explored in human-computer interaction and human-machine-interaction for facilitating hand-based interactions in applications such as prosthetics, virtual reality, robotic teleoperation, surface haptics, portable devices, and rehabilitation. This paper presents a technological overview of electrotactile feedback, as well a systematic review and meta-analysis of its applications for hand-based interactions. We discuss the different electrotactile systems according to the type of application. We also discuss over a quantitative congregation of the findings, to offer a high-level overview into the state-of-art and suggest future directions. Electrotactile feedback systems showed increased portability/wearability, and they were successful in rendering and/or augmenting most tactile sensations, eliciting perceptual processes, and improving performance in many scenarios. However, knowledge gaps (e.g., embodiment), technical (e.g., recurrent calibration, electrodes' durability) and methodological (e.g., sample size) drawbacks were detected, which should be addressed in future studies.Comment: 18 pages, 1 table, 8 figures, under review in Transactions on Haptics. This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessible.Upon acceptance of the article by IEEE, the preprint article will be replaced with the accepted versio

Multichannel electrotactile feedback with spatial and mixed coding for closed-loop control of grasping force in hand prostheses

Providing somatosensory feedback to the user of a myoelectric prosthesis is an important goal since it can improve the utility as well as facilitate the embodiment of the assistive system. Most often, the grasping force was selected as the feedback variable and communicated through one or more individual single channel stimulation units (e.g., electrodes, vibration motors). In the present study, an integrated, compact, multichannel solution comprising an array electrode and a programmable stimulator was presented. Two co ding schemes (15 levels), spatial and mixed (spatial and frequency) modulation, were tested in able-bodied subjects, psychometrically and in force control with routine grasping and force tracking using real and simulated prosthesis. The results demonstrated that mixed and spatial coding, although substantially different in psychometric tests, resulted in a similar performance during both force control tasks. Furthermore, the ideal, visual feedback was not better than the tactile feedback in routine grasping. To explain the observed results, a conceptual model was proposed emphasizing that the performance depends on multiple factors, including feedback uncertainty, nature of the task and the reliability of the feedforward control. The study outcomes, specific conclusions and the general model, are relevant for the design of closed-loop myoelectric prostheses utilizing tactile feedback

The impact of size and position of reference electrode on the localization of biphasic electrotactile stimulation on the fingertips

Development of haptic interfaces to enrich augmented and virtual reality with the sense of touch is the next frontier for technological advancement of these systems. Among available technologies, electrotactile stimulation enables design of high-density interfaces that can provide natural-like sensation of touch in interaction with virtual objects. The present study investigates the human perception of electrotactile sensations on fingertips, focusing on the sensation localization in function of the size and position of reference electrode. Ten healthy subjects participated in the study, with the task to mark the sensations elicited by stimulating the index fingertip using an 8-pad electrode. The test systematically explored several configurations of the active (position) and reference (position and size) electrode pads. The results indicated that there was a spreading of perceived sensations across the fingertip, but that they were mostly localized below the active pad. The position and size of the reference electrode were shown to affect the location of the perceived sensations, which can potentially be exploited as an additional parameter to modulate the feedback. The present study demonstrates that the fingertip is a promising target for the delivery of high-resolution feedback.The work in this study was performed within the TACTILITY project, which has received funding by European Union’s Horizon 2020 framework programme for research and innovation H2020-ICT-2018-2020/H2020-ICT 2018-3 under grant agreement no. 85671

Electrocutaneous stimulation to close the loop in myoelectric prosthesis control

Current commercially available prosthetic systems still lack sensory feedback and amputees are forced to maintain eye-contact with the prosthesis when interacting with their environment. Electrocutaneous stimulation is a promising approach to convey sensory feedback via the skin. However, when discussed in the context of prosthetic applications, it is often refused due to its supposed incompatibility with myocontrol. This dissertation now addresses electrocutaneous stimulation as means to provide sensory feedback to prosthesis users, and its implications on myoelectric control, possible use for improved or accelerated mastering of prosthesis control through closing of the control loop, as well as its potential in aiding in the embodiment of prosthetic components. First, a comparison of different paradigms for encoding sensory feedback variables in electrocutaneous stimulation patterns was done. For this, subject ability to employ spatially and intensity-coded electrocutaneous feedback in a simulated closed-loop control task was evaluated. The task was to stabilise an invisible virtual inverted pendulum under ideal feedforward control conditions (joystick). Pendulum inclination was either presented spatially (12 stimulation sites), encoded by stimulation strength (≧ 2 stimulation sites), or a combination of the two. The tests indicated that spatial encoding was perceived as more intuitive, but intensity encoding yielded better performance and lower energy expenditure. The second study investigated the detrimental influence of stimulation artefacts on myoelectric control of prostheses for a wide range of stimulation parameters and two prosthesis control approaches (pattern recognition of eight motion primitives, direct proportional control). Artefact blanking is introduced and discussed as a practical approach to handle stimulation artefacts and restore control performance back to the baseline. This was shown with virtual and applied artefact blanking (pattern recognition on six electromyographic channels), as well as in a practical task-related test with a real prosthesis (proportional control). The information transfer of sensory feedback necessary to master a routine grasping task using electromyographic control of a prosthesis was investigated in another study. Subjects controlled a real prosthesis to repeatedly grasp a dummy object, which implemented two different objects with previously unknown slip and fragility properties. Three feedback conditions (basic feedback on grasp success, visual grasp force feedback, tactile grasp force feedback) were compared with regard to their influence on subjects’ task performance and variability in exerted grasp force. It was found that online force feedback via a visual or tactile channel did not add significant advantages, and that basic feedback was sufficient and was employed by subjects to improve both performance and force variability with time. Importantly, there was no adverse effect of the additional feedback, either. This has important implications for other non-functional applications of sensory feedback, such as facilitation of embodiment of prosthetic devices. The final study investigated the impact of electrocutaneous stimulation on embodiment of an artificial limb. For this purpose, a sensor finger was employed in a rubber-hand-illusion-like experiment. Two independent groups (test, control), were compared with regard to two objective measures of embodiment: proprioceptive drift, and change in skin temperature. Though proprioceptive drift measures did not reveal differences between conditions, they indicated trends generally associated to a successful illusion. Additionally, significant changes in skin temperature between test and control group indicated that embodiment of the artificial digit could be induced by providing sensory substitution feedback on the forearm. In conclusion, it has been shown that humans can employ electrocutaneous stimulation feedback in challenging closed-loop control tasks. It was found that transition from simple intuitive encodings (spatial) to those providing better resolution (intensity) further improves feedback exploitation. Blanking and segmentation approaches facilitate simultaneous application of electrocutaneous stimulation and electromyographic control of prostheses, using both pattern recognition and classic proportional approaches. While it was found that force feedback may not aid in the mastering of routine grasping, the presence of the feedback was also found to not impede the user performance. This is an important implication for the application of feedback for non-functional purposes, such as facilitation of embodiment. Regarding this, it was shown that providing sensory feedback via electrocutaneous stimulation did indeed promote embodiment of an artificial finger, even if the feedback was applied to the forearm. Based on the results of this work, the next step should be integration of sensory feedback into commercial devices, so that all amputees can benefit from its advantages. Electrocutaneous stimulation has been shown to be an ideal means for realising this. Hitherto existing concerns about the compatibility of electrocutaneous stimulation and myocontrol could be resolved by presenting appropriate methods to deal with stimulation artefacts