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

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

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

Development of an Electrotactile Haptic Device with Application to Balance Rehabilitation

Balance impairments affect many individuals especially those in the older age bracket, and can lead to severe complications from falls. Research has shown that the cause of these impairments can be attributed to degraded sensory inputs. With ample sensory supplementation (or sensory augmentation), these deficiencies may be overcome. The purpose of this research is to verify a design of a low-cost custom electrotactile stimulation device that can aid in balance rehabilitation purposes. To this end, a major focus will be on wearability. Presently, there is a large research gap in the field of electrotactile stimulation for achieving wearable designs. Additionally, few devices incorporate a sensing mechanism for detecting balance impairment such as with an inertial measurement unit. Many researchers still rely on expensive commercial devices that are very large and bulky. Additionally, the design and implementation of electrotactile stimulation devices require working knowledge of circuits, thus there is mainly a general lack of instructions for the design of such devices. The thesis hopes to address these gaps by studying a design that may be simple to replicate from scratch. The design includes the use of several half H-bridge circuits to produce localized dipole stimulation through a 4 by 4 electrode array. Feasibility of the design will be verified via oscilloscope measurements and a small pilot study that is aimed at obtaining user feedback. The wearable components of the device include a custom-fabricated electrode array to be worn on the wrist or arm, and also an IMU (inertial measurement unit) belt along the waist to measure the user’s sway angle along the sagittal plane. Preliminary results show that a user can detect sensations from dry-skin stimulation while wearing the electrode array. The detected sensations also include directional information. Additionally, verification with the subject showed that the device is able to provide biofeedback through an electrode array as a result of the IMU orientation information. Further design refinements such as better point discrimination, pattern generation, and consistent pulsing are required before proceeding to the human testing and validation stage

Electrotactons: designing and evaluating electrotactile cues

Electrotactile feedback is a novel haptic feedback modality that can be used to evoke a desired level of alertness and emotion or convey multidimensional information to the user. However, there is a lack of research investigating its basic design parameters and how they can be used to create effective tactile cues. This thesis investigates the effect of Electrotactile feedback on the subjective perception of specific sensations, such as urgency, annoyance, valence and arousal, to find the number of distinguishable levels in each sensation. These levels are then used for designing structured, abstract, electrotactile messages called Electrotactons. These have potential benefits over vibration-based cues due to the greater flexibility of the actuators. Experiments 1, 2 & 4 investigated the effects of manipulating the basic electrotactile parameters pulse width, amplitude and pulse frequency on perceived sensations. The results showed that all parameters have a significant effect on the perceived sensations, except for pulse frequency not having an effect on valence. Also, pulse frequencies of 30 PPS and above did not influence the perceived sensations. Experiment 3 investigated the use of pulse width, amplitude and pulse frequency to convey three types of information simultaneously encoded into an electrotactile cue. This was the first attempt to design Electrotactons using the basic parameters of electrotactile feedback. The results showed overall recognition rates of 38.19% for the complete Electrotactons. For the individual component parameters, pulse width had a recognition rate of 71.67%, amplitude 70.27%, and pulse frequency 66.36%. Experiment 5 investigated intensity and pulse frequency to determine how many distinguishable levels could be perceived. Results showed that both intensity and pulse frequency significantly affected perception, with four distinguishable levels of intensity and two of pulse frequency. Experiment 6 investigated the use of intensity and pulse frequency from in Experiment 5 to improve the design of Electrotactons on three body locations using two different size electrodes. The results showed overall recognition rates of up to 65.31% for the complete Electrotactons. For the individual component parameters, intensity had a recognition rate of 68.68%, and pulse frequency 94.41%. These results add significant new knowledge about the parameter space of electrotactile cue design and help designers select suitable properties to use when creating electrotactile cues

Distributed Sensing and Stimulation Systems Towards Sense of Touch Restoration in Prosthetics

Modern prostheses aim at restoring the functional and aesthetic characteristics of the lost limb. To foster prosthesis embodiment and functionality, it is necessary to restitute both volitional control and sensory feedback. Contemporary feedback interfaces presented in research use few sensors and stimulation units to feedback at most two discrete feedback variables (e.g. grasping force and aperture), whereas the human sense of touch relies on a distributed network of mechanoreceptors providing high-fidelity spatial information. To provide this type of feedback in prosthetics, it is necessary to sense tactile information from artificial skin placed on the prosthesis and transmit tactile feedback above the amputation in order to map the interaction between the prosthesis and the environment. This thesis proposes the integration of distributed sensing systems (e-skin) to acquire tactile sensation, and non-invasive multichannel electrotactile feedback and virtual reality to deliver high-bandwidth information to the user. Its core focus addresses the development and testing of close-loop sensory feedback human-machine interface, based on the latest distributed sensing and stimulation techniques for restoring the sense of touch in prosthetics. To this end, the thesis is comprised of two introductory chapters that describe the state of art in the field, the objectives and the used methodology and contributions; as well as three studies distributed over stimulation system level and sensing system level. The first study presents the development of close-loop compensatory tracking system to evaluate the usability and effectiveness of electrotactile sensory feedback in enabling real-time close-loop control in prosthetics. It examines and compares the subject\u2019s adaptive performance and tolerance to random latencies while performing the dynamic control task (i.e. position control) and simultaneously receiving either visual feedback or electrotactile feedback for communicating the momentary tracking error. Moreover, it reported the minimum time delay needed for an abrupt impairment of users\u2019 performance. The experimental results have shown that electrotactile feedback performance is less prone to changes with longer delays. However, visual feedback drops faster than electrotactile with increased time delays. This is a good indication for the effectiveness of electrotactile feedback in enabling close- loop control in prosthetics, since some delays are inevitable. The second study describes the development of a novel non-invasive compact multichannel interface for electrotactile feedback, containing 24 pads electrode matrix, with fully programmable stimulation unit, that investigates the ability of able-bodied human subjects to localize the electrotactile stimulus delivered through the electrode matrix. Furthermore, it designed a novel dual parameter -modulation (interleaved frequency and intensity) and compared it to conventional stimulation (same frequency for all pads). In addition and for the first time, it compared the electrotactile stimulation to mechanical stimulation. More, it exposes the integration of virtual prosthesis with the developed system in order to achieve better user experience and object manipulation through mapping the acquired real-time collected tactile data and feedback it simultaneously to the user. The experimental results demonstrated that the proposed interleaved coding substantially improved the spatial localization compared to same-frequency stimulation. Furthermore, it showed that same-frequency stimulation was equivalent to mechanical stimulation, whereas the performance with dual-parameter modulation was significantly better. The third study presents the realization of a novel, flexible, screen- printed e-skin based on P(VDF-TrFE) piezoelectric polymers, that would cover the fingertips and the palm of the prosthetic hand (particularly the Michelangelo hand by Ottobock) and an assistive sensorized glove for stroke patients. Moreover, it developed a new validation methodology to examine the sensors behavior while being solicited. The characterization results showed compatibility between the expected (modeled) behavior of the electrical response of each sensor to measured mechanical (normal) force at the skin surface, which in turn proved the combination of both fabrication and assembly processes was successful. This paves the way to define a practical, simplified and reproducible characterization protocol for e-skin patches In conclusion, by adopting innovative methodologies in sensing and stimulation systems, this thesis advances the overall development of close-loop sensory feedback human-machine interface used for restoration of sense of touch in prosthetics. Moreover, this research could lead to high-bandwidth high-fidelity transmission of tactile information for modern dexterous prostheses that could ameliorate the end user experience and facilitate it acceptance in the daily life

Creating tactile feedback with intelligent electrical stimulation to compensate for sensory impairment.

Performing daily life activities can be more challenging as a result of peripheral neuropathy in the feet and can lead to an increased risk of falls and injuries. Biofeedback, in the form of electrocutaneous stimulation, can be used as a means to transmit information about the force and pressure applied to the feet, and this can help people determine their body position in relation to the ground and the amount of sway movements. The motivation for the present work was to explore whether a wearable electrotactile feedback system (EFS) could improve life quality by supporting people with balance instability as a result of this condition. In this study a wearable EFS was designed to estimate the magnitude of pressure applied to the feet during standing and walking. The study also aimed to determine whether the EFS had an effect on posture control in standing and confidence in walking among individuals suffering from peripheral neuropathy. A wearable EFS has been developed in this work including the hardware design for an electrocutaneous stimulation and a processing unit to compute the sensor data. The EFS uses a sensor system with piezoresitive force sensors that has been developed and tested beforehand. The proposed system considers aspects of safety and portability, as well as meeting individual parameters. The latter one was assured by implementing and testing a novel calibration method for the detection of sensory thresholds and device parameters. A software for magnitude estimation and force and pressure feedback based on the centre of pressure (COP) movement was programmed and a psychophysical transfer function involving sensory thresholds and sensor system variables was implemented. A pilot study with 11 participants was carried out to evaluate the suitability of the EFS for magnitude estimation. Magnitude estimation with the EFS showed high accuracy and sensitivity and it was found that the design proposed in this work is beneficial over other solutions. The upper leg was identified as a suitable location for electrotactile feedback. A proof of concept study was undertaken among 14 individuals suffering with peripheral neuropathy and five controls in a clinical environment, testing the effects of the EFS on balancing and walking in different scenarios. It was shown that, when used by patients with neuropathy, the EFS helped improving posture control in certain scenarios and did not hinder patients during walking. A longer learning period might be necessary so that users can fully benefit from the EFS. The findings of the study contribute to the understanding of electrotactile feedback and are valuable for further developments of wearable EFS to compensate for sensory impairment and improve activities of daily life for people with sensation loss in their feet

Mechanisms for enabling closed-loop upper limb sensorimotor prosthetic control

Myoelectric upper limb prostheses are limited in their ability to provide sensory feedback to a user. The lack of sensory feedback forces prosthesis users to rely on visual feedback alone in manipulating objects, and often leads to abandonment of the prosthesis in favor of the user's unimpaired arm. Consequently, there is a critical need to develop mechanisms that enable people with upper limb amputations to be able to receive sensory feedback from the environment. The goal of this dissertation is to describe the development and evaluation of various mechanisms that enable simultaneous myoelectric control of hand prostheses with proprioceptive and touch/pressure feedback. Sensory feedback is enabled through the use of a passive skin stretch mechanism for proprioception (Chapter 2), an epidermal electronic device that can provide electrotactile stimulation (Chapter 3), and a custom-built prosthetic hand that relays contact and pressure information from the fingertips (Chapter 4). In each of these chapters, motor control is simultaneously enabled through the use of electromyographic sensors. The remainder of the dissertation focuses on a method of enabling long-term wear of electrotactile stimulation electrodes by modeling (Chapter 5) and controlling (Chapter 6) sensation intensity in response to changes in the impedance of the electrode-skin interface. The techniques described in this dissertation have the potential to improve prosthesis embodiment for a person with an upper limb amputation, with the ultimate goal of reducing prosthesis abandonment and improving quality of life