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).

Non-informative vision improves spatial tactile discrimination on the shoulder but does not influence detection sensitivity.

Vision of the body has been reported to improve tactile acuity even when vision is not informative about the actual tactile stimulation. However, it is currently unclear whether this effect is limited to body parts such as hand, forearm or foot that can be normally viewed, or it also generalizes to body locations, such as the shoulder, that are rarely before our own eyes. In this study, subjects consecutively performed a detection threshold task and a numerosity judgment task of tactile stimuli on the shoulder. Meanwhile, they watched either a real-time video showing their shoulder or simply a fixation cross as control condition. We show that non-informative vision improves tactile numerosity judgment which might involve tactile acuity, but not tactile sensitivity. Furthermore, the improvement in tactile accuracy modulated by vision seems to be due to an enhanced ability in discriminating the number of adjacent active electrodes. These results are consistent with the view that bimodal visuotactile neurons sharp tactile receptive fields in an early somatosensory map, probably via top-down modulation of lateral inhibition.

Developing a mobile exercise program for individuals with Spinal Cord Injury: Stakeholder perceptions of app features and implementation determinants.

BACKGROUND: Individuals with Spinal Cord Injury (SCI) often experience physical deconditioning, leading to long-term health challenges. While regular exercise can offer substantial health benefits, adherence to exercise guidelines among individuals with SCI is hindered by barriers such as inaccessibility. Exercise programs using the mobile application (App) tailored to individual needs present a promising solution for promoting exercise adherence among individuals with SCI. OBJECTIVE: This study aimed to identify factors contributing to the successful implementation of an app-based home exercise program for individuals with SCI and gather user feedback on app preferences, functionality, and features. METHODS: Guided by the Consolidated Framework for Implementation Research (CFIR), twenty-six clinicians completed an expert panel survey to rank factors influencing the implementation of an app-based intervention for increasing exercise adherence for individuals with SCI. CFIR-selected factors and app quality features obtained from the Mobile Application Rating Scale (MARS) framework were discussed in seven focus groups with 23 individuals with SCI, 6 caregivers, and 6 clinicians. RESULTS: The expert survey identified adaptability, complexity, evidence strength/quality, relative advantage, knowledge/beliefs about the initiative, and execution as the key CFIR factors that affected the intervention's success. Major themes emerging from focus groups with individuals with SCI and caregivers included usability, instruction and guidelines, user-friendly interface, and clinician interaction. In contrast, clinicians mentioned themes such as the representation of the SCI population, time commitment, accessibility, and equipment. CONCLUSIONS: The study highlights the significance of incorporating these determinants into future designs to develop app-based home exercise interventions for individuals with SCI.

Temporal Asynchrony but Not Total Energy Nor Duration Improves the Judgment of Numerosity in Electrotactile Stimulation.

Stroke patients suffer from impairments of both motor and somatosensory functions. The functional recovery of upper extremities is one of the primary goals of rehabilitation programs. Additional somatosensory deficits limit sensorimotor function and significantly affect its recovery after the neuromotor injury. Sensory substitution systems, providing tactile feedback, might facilitate manipulation capability, and improve patient's dexterity during grasping movements. As a first step toward this aim, we evaluated the ability of healthy subjects in exploiting electrotactile feedback on the shoulder to determine the number of perceived stimuli in numerosity judgment tasks. During the experiment, we compared four different stimulation patterns (two simultaneous: short and long, intermittent and sequential) differing in total duration, total energy, or temporal synchrony. The experiment confirmed that the subject ability to enumerate electrotactile stimuli decreased with increasing the number of active electrodes. Furthermore, we found that, in electrotactile stimulation, the temporal coding schemes, and not total energy or duration modulated the accuracy in numerosity judgment. More precisely, the sequential condition resulted in significantly better numerosity discrimination than intermittent and simultaneous stimulation. These findings, together with the fact that the shoulder appeared to be a feasible stimulation site to communicate tactile information via electrotactile feedback, can serve as a guide to deliver tactile feedback to proximal areas in stroke survivors who lack sensory integrity in distal areas of their affected arm, but retain motor skills.

Vibrotactile feedback to control the amount of weight shift during walking - A first step towards better control of an exoskeleton for spinal cord injury subjects.

People with Spinal Cord Injury do not only lack the ability to control their muscles, but also miss the sensory information from below the level of their lesion. Therefore, it may become difficult for them to perceive the state of the body during walking, which is however often used to control wearable exoskeletons. In the present study the possibilities of providing vibrotactile feedback about the Center of Mass (CoM) during walking were investigated. The results showed that healthy subjects could successfully interpret the provided vibrotactile cues and change their walking pattern accordingly. Vibrotactile stimulation was either provided in a concurrent (over the complete CoM movement) or terminal (only when the desired CoM displacement was reached) way. The latter led to a better accuracy and can be easily implemented in a wearable exoskeleton where a certain amount of CoM displacement is needed to initiate stepping.