Perceptual correlates of successful body-prosthesis interaction in lower limb amputees: psychometric characterisation and development of the Prosthesis Embodiment Scale

Development and validation of the Persian Prosthesis Embodiment Scale for Lower Limb Amputees

PURPOSE

To investigate the psychometric features of the Persian version of the recently introduced Prosthesis Embodiment Scale for Lower Limb Amputees (PEmbS-LLA), as well its revised form.

MATERIALS AND METHODS

In this cross-sectional study, the translation process for the PEmbS-LLA followed internationally recommended guidelines. Scale reliability was determined by assessing internal consistency and test-retest reliability (after two weeks) using Cronbach's alpha and Spearman's correlation coefficients, respectively. The validity was evaluated using the Persian Trinity Amputation and Prosthetic Experience Scales (TAPES). We compared our findings to that obtained in a German sample.

RESULTS

With a total of 126 persons with lower limb amputation participating in the study, the Persian PEmbS-LLA showed good internal consistency (Cronbach's alpha ≥0.79) and test-retest reliability (Spearman's Rho ≥0.83). There were small to moderate correlations between the Persian PEmbS-LLA and TAPES subscales. Factor analysis revealed only one component with eigenvalue larger than 1, explaining 69.72% of the variance and suggesting unidimensionality. The PEmbS-LLA total score in the Iranian sample was significantly lower than in the German sample (p < 0.01).

CONCLUSIONS

The Persian PEmbS-LLA is a valid and reliable instrument. Interpretation of significant differences in prosthesis embodiment between the samples requires further research.

The German adaptation of the Amputee Body Image Scale and the importance of psychosocial adjustment to prosthesis use

Negative cognitions related to one's own body, here referred to as body image disturbances (BID), are common after lower limb amputation and correlate with weak psychological functioning. The Amputee Body Image Scale (ABIS) is internationally used to assess BID in persons with lower limb amputation. However, there is no psychometrically evaluated German adaptation available. Including a sample of 191 individuals with lower limb amputation, the present study developed and psychometrically evaluated the German ABIS. Results suggest high reliability in terms of internal consistency and stability of the measure over two years. Meaningful and significant relationships to sex, amputation level, post-amputation pain, mobility, and psychopathology indicate validity of the instrument. Multivariate analyses emphasize a specific and inverse relationship between BID and psychosocial adaptation to the prosthesis including its embodiment. Focussing on ABIS items that are independent of the type of amputation or rehabilitation experiences resulted in an ABIS short form with psychometric properties comparable to the long form. This instrument could be prospectively used in diverse limb loss populations, such as individuals with upper limb amputation or persons not using a prosthesis. The present results thus crucially contribute to the repertoire of patient-reported outcome measures in the context of post-amputation rehabilitation.

PhantomAR: gamified mixed reality system for alleviating phantom limb pain in upper limb amputees-design, implementation, and clinical usability evaluation

BACKGROUND

Phantom limb pain (PLP) is a restrictive condition in which patients perceive pain in a limb that is no longer present, greatly reducing their quality of life. Mirror Therapy, wherein patients observe a mirror reflection of their intact limb, has demonstrated efficacy in alleviating PLP. However, its unilateral and seated nature presents limitations. To address these constraints while still reducing PLP, and evaluating the impact of different virtual limb representations (anthropomorphic vs. non-anthropomorphic) on the user's sense of ownership, agency, and embodiment, PhantomAR was developed. Leveraging wearable first-person augmented reality (AR) technology, PhantomAR extends traditional Mirror Therapy by enabling users to move freely and engage in bimanual tasks.

METHODS

The assistive mixed reality game application PhantomAR was deployed on the Microsoft HoloLens 2 and augmented the user's residual limb by superimposing a virtual arm or tentacle that was controlled via residual muscles on their stump using an EMG electrode array. This setup allowed patients to engage in a first-person perspective and manipulate virtual objects with both the healthy and augmented limbs, free from the confines of a seated position. The study enrolled 10 able-bodied individuals and 8 individuals with unilateral, transradial amputation. All amputees experienced PLP. The usability of the PhantomAR application was evaluated using the System Usability Scale (SUS) and a user-centric survey. Additionally, the Game Experience was assessed on a 5-point Likert questionnaire (GEQ). Participants rated their phantom sensations using the Numerical Rating Scale and McGill Pain Questionnaire before, during, and after interaction with PhantomAR. The embodiment and agency of the virtual superimposed arm were evaluated with an altered Prosthesis Embodiment Scale. The study protocol included two sessions of 30 min each, during which participants experienced PhantomAR.

RESULTS

Participants (n = 18) rated PhantomAR highly usable (SUS m = 90.8%, SD = 6.88). Feedback on the Game Experience Questionnaire was overwhelmingly positive, showing high immersion (m = 4.46, SD = 0.08) and positive affect (m = 4.97, SD = 0.05). PLP (n = 8) significantly decreased post-intervention (NRS and McGill Pain Questionnaire, p < .001). Skin temperature in the residual limb increased significantly post-intervention (p < .01) but did not correlate with PLP (r = - 0.08, p = 0.83). Tentacle overlay yielded mixed ownership but high agency ratings.

CONCLUSION

PhantomAR leverages mixed reality to significantly reduce Phantom Limb Pain, enhance user engagement, and alter perceptions of ownership and agency of their augmented limb through bi-manual, dynamic, full-body interactions. Trial registration DRKS00033208 (Jan. 5th 2024).

Examining the physical and psychological effects of combining multimodal feedback with continuous control in prosthetic hands

Myoelectric prosthetic hands are typically controlled to move between discrete positions and do not provide sensory feedback to the user. In this work, we present and evaluate a closed-loop, continuous myoelectric prosthetic hand controller, that can continuously control the position of multiple degrees of freedom of a prosthesis while rendering proprioceptive feedback to the user via a haptic feedback armband. Twenty-eight participants without and ten participants with upper limb difference (ULD) were recruited to holistically evaluate the physical and psychological effects of the controller via isolated control and sensory tasks, dexterity assessments, embodiment and task load questionnaires, and post-study interviews. The combination of proprioceptive feedback and continuous control enabled more accurate position and force modulation than without proprioceptive feedback, and restored blindfolded object identification ability to open-loop discrete controller levels. Dexterity assessment and embodiment questionnaire results revealed no significant physical performance or psychological embodiment differences between control types, with the exception of perceived sensation questions, which were significantly higher (p < 0.001) for closed-loop controllers. Key differences between participants with and without ULD were identified, including increasingly lower perceived body completeness and heterogeneity in frustration in participants with ULD, which can inform future development and rehabilitation.

Reliability and validity of the Turkish version of the Prosthesis Embodiment Scale for Lower Limb Amputees

BACKGROUND

Prosthetic embodiment is the perception of the prosthesis as a part of the body, and it is important for acceptance and adequate and effective use of the prosthesis.

OBJECTIVE

The aim of this study was to investigate the validity and reliability of the Turkish version of the Prosthesis Embodiment Scale for Lower Limb Amputees.

METHODS

This cross-sectional study included a total of 88 lower limb amputees. Internal consistency was evaluated using Cronbach α coefficient. The test-retest reliability of the scale, which was reapplied after 7-10 d, was evaluated using intraclass correlation coefficient. Principal component analysis with Varimax rotation was used to analyze the factor structure. Spearman correlation coefficient with Trinity Amputation and Prosthesis Experience Scale subscales was calculated for concurrent validity.

RESULTS

The mean age of the participants was 45.13 ± 15.05 years, and 76.1% were male. Internal consistency (Cronbach α = 0.905) and test-retest reliability (intraclass correlation coefficient = 0.822) were high. 76.1% of the total variance could be explained by the 3 dimensions. Significant correlation was found with the Trinity Amputation and Prosthesis Experience Scale subscales (r = 0.542 for psychosocial adjustment subscale, r = -0.452 for activity restriction subscale, r = 0.490 for prosthesis satisfaction subscale, p < 0.001).

CONCLUSIONS

The results of this study showed that the Turkish version of the Prosthesis Embodiment Scale for Lower Limb Amputees is a valid and reliable tool that can be used to evaluate prosthetic rehabilitation outcomes.

Human factors considerations of Interaction between wearers and intelligent lower-limb prostheses: a prospective discussion

Compared to traditional lower-limb prostheses (LLPs), intelligent LLPs are more versatile devices with emerging technologies, such as microcontrollers and user-controlled interfaces (UCIs). As emerging technologies allow a higher level of automation and more involvement from wearers in the LLP setting adjustments, the previous framework established to study human factors elements that affect wearer-LLP interaction may not be sufficient to understand the new elements (e.g., transparency) and dynamics in this interaction. In addition, the increased complexity of interaction amplifies the limitations of the traditional evaluation approaches of wearer-LLP interaction. Therefore, to ensure wearer acceptance and adoption, from a human factors perspective, we propose a new framework to introduce elements and usability requirements for the wearer-LLP interaction. This paper organizes human factors elements that appear with the development of intelligent LLP technologies into three aspects: wearer, device, and task by using a classic model of the human-machine systems. By adopting Nielsen's five usability requirements, we introduce learnability, efficiency, memorability, use error, and satisfaction into the evaluation of wearer-LLP interaction. We identify two types of wearer-LLP interaction. The first type, direct interaction, occurs when the wearer continuously interacts with the intelligent LLP (primarily when the LLP is in action); the second type, indirect interaction, occurs when the wearer initiates communication with the LLP usually through a UCI to address the current or foreseeable challenges. For each type of interaction, we highlight new elements, such as device transparency and prior knowledge of the wearer with the UCI. In addition, we redefine the usability goals of two types of wearer-LLP interaction with Nelson's five usability requirements and review methods to evaluate the interaction. Researchers and designers for intelligent LLPs should consider the new device elements that may additionally influence wearers' acceptance and the need to interpret findings within the constraints of the specific wearer and task characteristics. The proposed framework can also be used to organize literature and identify gaps for future directions. By adopting the holistic usability requirements, findings across empirical studies can be more comparable. At the end of this paper, we discuss research trends and future directions in the human factors design of intelligent LLPs.

The impact of a customized aesthetic prosthetic leg cover on social interaction cues and attitudes in the general UK population: Two experimental studies

OBJECTIVES

To explore the impact of an aesthetic prosthetic leg cover on attitudes toward individuals with lower-limb amputation and associated social interaction cues among the general UK population.

STUDY DESIGN

Two novel experimental methodologies.

METHODS

In study 1, participants (n = 188) viewed 1 of 3 images of an individual: (1) wearing a traditional stem prosthetic, (2) wearing an aesthetic leg cover, or (3) as a nonamputee. They then completed an attitude scale and rated the personality of the individual using the 10-item Big Five Inventory. Study 2 (n = 31) used eye tracking and facial expression software to explore gaze and facial arousal when viewing 1 of 9 manipulated videos of the same individual talking about 3 different scenarios.

RESULTS

In study 1, the aesthetic leg cover led to significantly higher ratings of agreeableness than stem and nonamputee images and significantly higher ratings of extraversion than the nonamputee image. Attitudes toward an individual with a prosthesis did not significantly differ depending on which image they viewed and were generally positive. In study 2, all participants focused mainly on the individual's face regardless of scenario topic or leg condition, although participants focused more around the leg cover in more active contexts.

CONCLUSIONS

Customized aesthetic leg covers may help individuals living with amputation to be perceived more positively in social situations. These experimental methodologies could be extended to explore the differential impact of context, functionality, and activity of specific types of customized aesthetic prosthetics and could help inform shared decision-making processes in clinical settings.

Development and Preliminary Evaluation of a Bimodal Foot Prosthesis for Walking and Running

People often alternate between bouts of walking and running, for instance, when adults participate in recreational activities. Transitioning between activities can be challenging for prosthesis users because existing prosthetic feet are not well-suited for both tasks. Meanwhile, switching between prostheses for different tasks is often impractical. Collectively, these challenges can present barriers to physical activity participation for people with limb loss, which can negatively impact social or physical health. This work describes the development and evaluation of a passive bimodal prosthetic foot prototype with different configurations and stiffnesses for walking and running. Users rated the bimodal prosthesis higher for standing and walking compared to a running prosthesis (+2.3 for both tasks on a seven-point Likert scale). Users rated the bimodal prosthesis higher for running compared to a walking prosthesis (+1.7 and +0.5 for 2.0 and 2.5 m/s running, respectively). Changing from walking to running mode increased the device's stiffness by 23-84%, depending on the user's preference. Users could switch between bimodal prosthesis walking and running modes quickly (21.3 ± 12.0 s). Overall, the preliminary results were encouraging in terms of user satisfaction, stiffness change between modes, and mode-switching speed. These findings motivate future exploration of this bimodal prosthesis concept.

[Validated German PROMs for People with Major Amputation of the Lower Extremity - A Narrative Review Based on the Final Report of the LEAD and COMPASS Initiative of the ISPO]

Patient-reported outcome measures (PROMs) play an important role in the rehabilitation of people with major limb amputations. Patient-completed questionnaires help collect specific constructs on this patient population. The COMPASS and LEAD initiatives, carried out by the International Society for Prosthetics and Orthotics (ISPO), underscore the importance of regularly collecting high-quality PROMs. These are essential for the evaluation of rehabilitation needs, progress, and success. In the final report of ISPO's major international initiative, PROMs recommendations of the expert panel are tabulated. In Table 3.2 of the report, ISPO lists n=12 PROMs that were included in the narrow consensus process were considered to be of acceptable quality, and therefore recommended. The aim of this systematic review was to specifically search for these recommended PROMS regarding their availability in a German and validated version in order to identify potential gaps. All PROMs that were available in a German and validated version were then examined further with regard to the quality of the validation study, using the checklist of COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN). Through a systematic literature search, six validated German-language versions were found. Only four of these met the quality standards of the COSMIN checklist sufficiently. Overall, this review shows serious gaps in the availability in the German language of validated versions of PROMs used internationally and recommended as standard by the ISPO. This gap needs to be closed by guideline-oriented translation and subsequent validation studies in order to be able to offer and collect the PROMS recommended by the ISPO also for German-speaking patient populations.

Resting state neurophysiology of agonist-antagonist myoneural interface in persons with transtibial amputation

The agonist-antagonist myoneural interface (AMI) is an amputation surgery that preserves sensorimotor signaling mechanisms of the central-peripheral nervous systems. Our first neuroimaging study investigating AMI subjects conducted by Srinivasan et al. (2020) focused on task-based neural signatures, and showed evidence of proprioceptive feedback to the central nervous system. The study of resting state neural activity helps non-invasively characterize the neural patterns that prime task response. In this study on resting state functional magnetic resonance imaging in AMI subjects, we compared functional connectivity in patients with transtibial AMI (n = 12) and traditional (n = 7) amputations (TA). To test our hypothesis that we would find significant neurophysiological differences between AMI and TA subjects, we performed a whole-brain exploratory analysis to identify a seed region; namely, we conducted ANOVA, followed by t-test statistics to locate a seed in the salience network. Then, we implemented a seed-based connectivity analysis to gather cluster-level inferences contrasting our subject groups. We show evidence supporting our hypothesis that the AMI surgery induces functional network reorganization resulting in a neural configuration that significantly differs from the neural configuration after TA surgery. AMI subjects show significantly less coupling with regions functionally dedicated to selecting where to focus attention when it comes to salient stimuli. Our findings provide researchers and clinicians with a critical mechanistic understanding of the effect of AMI amputation on brain networks at rest, which has promising implications for improved neurorehabilitation and prosthetic control.

Rasch validation of the German version of the Prosthesis Embodiment Scale for lower limb amputees and proposal of a revised version

PURPOSE

To perform a detailed psychometric Rasch analysis of the Prosthesis Embodiment Scale (PEmbS) administered in adults with lower limb amputation (LLA).

METHODS

A convenience sample of German-speaking adults with LLA (n = 150), recruited from German state agencies' databases, was asked to complete the PEmbS, a 10-item patient-reported scale assessing prosthesis embodiment.

RESULTS

The local dependency between two items was resolved by keeping for the global score only the lower score of these two items (#9 and #10). Collapsing the seven response categories to four (two expressing disagreement and two agreement) eliminated disordered thresholds. After that, the PEmbS demonstrated unidimensionality, acceptable item fit, and good reliability indices. A keyform plot was created to transform raw scores into linear measures of prosthesis embodiment, making it possible to compare the individual's item responses with those expected by the Rasch model, and to manage missing responses.

CONCLUSIONS

The PEmbS is useful for assessing prosthesis embodiment in people with LLA, both for research and clinical purposes. We propose a revised version of the PEmbS for lower limb amputees; its appropriateness in other LLA contexts requires further investigation.

Lower-Limb Myoelectric Calibration Postures for Transtibial Prostheses

The use of an agonist-antagonist muscle pair for myoelectric control of a transtibial prosthesis requires normalizing the myoelectric signals and identifying their co-contraction signature. Extensive literature has explored the relationship between body posture and lower-limb muscle activation level using surface electromyography (EMG), but it is unknown how these relationships hold after amputation. Using a virtual tracking task, this study compares the effect of three different calibration postures (seated, standing, dynamic) on user tracking ability while in two tracking postures (seated, standing) for 18 able-bodied (AB) subjects and 9 subjects with transtibial (TT) amputation. As expected, AB subjects produced statistically significant differences in muscle activation for gastrocnemius (GAS) when seated vs. standing during calibration (p = 8.8e-4), but not for tibialis anterior (TA) (p = 0.76). TT subjects, however, showed no significant differences in GAS or TA between seated and standing (p = 0.90, 0.60 respectively). It was also determined that normalizing EMG by the global maximum signal observed (standard in biomechanic analysis) is undesirable for myoelectric control. For best general results with this framework, calibration in both seated and dynamic postures is recommended, taking the normalization information from the seated posture and the narrowest co-contraction slopes from the two.

Rasch validation of the German translation of the Prosthetic Limb Users Survey of Mobility short forms in people with lower limb amputation

BACKGROUND

Prostheses are a primary rehabilitative intervention for people after lower limb amputation. To appropriately measure the effectiveness of prosthetic interventions, valid and reliable measures of prosthetic mobility are required. The Prosthetic Limb Users Survey of Mobility (PLUS-M) is a promising instrument for measuring prosthesis users' mobility. However, German translations of the PLUS-M short forms have not yet been validated.

OBJECTIVES

Rasch validation of the German translation of the PLUS-M short forms in people with lower limb amputation.

STUDY DESIGN

This study is based on a cross-sectional survey of prosthesis-using lower limb amputees from a nation-wide cohort.

METHODS

PLUS-M data (the 7-item and the 12-item shortforms; PLUS-M-7 and PLUS-M-12, respectively) from 194 lower limb prosthesis users were subjected to Rasch analysis, an advanced statistical method for assessing if the measurement properties of a questionnaire comply with a wide spectrum of psychometric requirements.

RESULTS

Analysis showed appropriate rating scale functioning, good internal construct validity (item fit), unidimensionality, and good targeting of the PLUS-M-7 and PLUS-M-12 short forms. Moreover, the greater conditional measurement precision of PLUS-M-12 (regarding higher test information and lower standard error of mobility estimates) was quantified.

CONCLUSIONS

Rasch analysis of the German translation of both PLUS-M short forms showed good psychometric qualities. In addition, our study showed that test scores from the PLUS-M-12 are more accurate. Therefore, the PLUS-M-12 is recommended for individual-level clinical applications (e.g., classification or change assessment).

A framework for understanding prosthetic embodiment for the plastic surgeon

Plastic surgeons play a critical role in the management of amputations and are uniquely positioned to improve the lives and functional abilities of patients with limb loss. The embodiment of a prosthesis describes how effectively it replaces a missing limb and is an important aspect of patient care. Despite its importance, the current prosthetics literature lacks a formal definition of embodiment, and descriptions are often vague or incomplete. In this narrative review, we assess the current literature on prosthetic embodiment to explore the main mechanisms of embodiment and how each allows a prosthesis to interface with the human body. In doing so, we provide a comprehensive, holistic framework for understanding this concept.

Resting state neurophysiology of agonist-antagonist myoneural interface in persons with transtibial amputation

The agonist-antagonist myoneural interface (AMI) is a novel amputation surgery that preserves sensorimotor signaling mechanisms of the central-peripheral nervous systems. Our first neuroimaging study investigating AMI subjects (Srinivasan et al., Sci. Transl. Med. 2020) focused on task-based neural signatures, and showed evidence of proprioceptive feedback to the central nervous system. The study of resting state neural activity helps non-invasively characterize the neural patterns that prime task response. In this first study on resting state fMRI in AMI subjects, we compared resting state functional connectivity in patients with transtibial AMI (n=12) and traditional (n=7) amputations, as well as biologically intact control subjects (n=10). We hypothesized that the AMI surgery will induce functional network reorganization that significantly differs from the traditional amputation surgery and also more closely resembles the neural configuration of controls. We found AMI subjects to have lower connectivity with salience and motor seed regions compared to traditional amputees. Additionally, with connections affected in traditional amputees, AMI subjects exhibited a connectivity pattern more closely resembling controls. Lastly, sensorimotor connectivity in amputee cohorts was significantly associated with phantom sensation (R2=0.7, p=0.0008). These findings provide researchers and clinicians with a critical mechanistic understanding of the effects of the AMI surgery on the brain at rest, spearheading future research towards improved prosthetic control and embodiment.

Recommendations from the ISPO lower-limb COMPASS: Patient-reported and performance-based outcome measures

BACKGROUND

Outcome measures (patient-reported and performance-based) are used widely but not uniformly within the clinical setting for individuals with lower-limb absence (LLA). The need for more detailed information by funding bodies, service planners and providers, and researchers requires the systematic and routine use of outcome measures. Currently, there is no consensus on which outcome measure(s) should be used for individuals with LLA. The aim of the International Society of Prosthetics and Orthotics (ISPO) lower-limb Consensus Outcome Measures for Prosthetic and Amputation Services (COMPASS) was to produce a recommended list of outcome measures to be actively promoted for routine use within clinical practice before and after an episode of care.

METHODS

Between May and June 2021, 46 users, clinicians, researchers, managers, and policymakers working in the field of LLA and prosthetic users met virtually. Consensus participants were first asked to complete an online survey with questions based on the results from a systematic review and the outcomes from an expert panel. A modified Delphi technique was used to determine outcome measures for use in routine clinical practice. This paper discusses the ISPO lower-limb COMPASS process from which recommendations were made.

RESULTS

The ISPO lower-limb COMPASS resulted in the following 6 recommendations: (1) Amputee Mobility Predictor, Timed Up and Go, Two-Minute Walk Test, Prosthetic Evaluation Questionnaire-Residual Limb Health, Prosthetic Evaluation Questionnaire-Utility, and Trinity Amputation and Prosthesis Experience Scales-Revised, which make up the ISPO lower-limb COMPASS ; (2) Comprehensive High-Level Activity Mobility Predictor and Six-Minute Walk Test are 2 additional outcome measures recommended for higher-activity-level individuals with LLA, which make up the COMPASS+ ; (3) Patient-Specific Function Scale makes up the COMPASS Adjunct ; (4) a generic health-related quality of life outcome measure such as the European Quality of Life-5D-5L or Patient-Reported Outcomes Measurement Information System-29 item can be used to supplement the COMPASS; (5) outcome measures suited to low- and middle-income countries need to be developed with a focus on activities such as sitting cross-legged, kneeling, squatting, and other culturally important mobility-related activities; and (6) translation, validation, and open sharing of translated outcome measures included in the COMPASS, COMPASS+, and COMPASS Adjunct occurs.

CONCLUSION

The above recommendations represent the current status of knowledge on outcome measures for LLA based on research and international consensus and hence, will change over time. This work has been developed for clinicians and researchers to improve knowledge on outcome measures to guide clinical decision-making and future research initiatives.

Haptic shared control improves neural efficiency during myoelectric prosthesis use

Clinical myoelectric prostheses lack the sensory feedback and sufficient dexterity required to complete activities of daily living efficiently and accurately. Providing haptic feedback of relevant environmental cues to the user or imbuing the prosthesis with autonomous control authority have been separately shown to improve prosthesis utility. Few studies, however, have investigated the effect of combining these two approaches in a shared control paradigm, and none have evaluated such an approach from the perspective of neural efficiency (the relationship between task performance and mental effort measured directly from the brain). In this work, we analyzed the neural efficiency of 30 non-amputee participants in a grasp-and-lift task of a brittle object. Here, a myoelectric prosthesis featuring vibrotactile feedback of grip force and autonomous control of grasping was compared with a standard myoelectric prosthesis with and without vibrotactile feedback. As a measure of mental effort, we captured the prefrontal cortex activity changes using functional near infrared spectroscopy during the experiment. It was expected that the prosthesis with haptic shared control would improve both task performance and mental effort compared to the standard prosthesis. Results showed that only the haptic shared control system enabled users to achieve high neural efficiency, and that vibrotactile feedback was important for grasping with the appropriate grip force. These results indicate that the haptic shared control system synergistically combines the benefits of haptic feedback and autonomous controllers, and is well-poised to inform such hybrid advancements in myoelectric prosthesis technology.

Measuring embodiment: A review of methods for prosthetic devices

The development of neural interfaces to provide improved control and somatosensory feedback from prosthetic limbs has initiated a new ability to probe the various dimensions of embodiment. Scientists in the field of neuroprosthetics require dependable measures of ownership, body representation, and agency to quantify the sense of embodiment felt by patients for their prosthetic limbs. These measures are critical to perform generalizable experiments and compare the utility of the new technologies being developed. Here, we review outcome measures used in the literature to evaluate the senses of ownership, body-representation, and agency. We categorize these existing measures based on the fundamental psychometric property measured and whether it is a behavioral or physiological measure. We present arguments for the efficacy and pitfalls of each measure to guide better experimental designs and future outcome measure development. The purpose of this review is to aid prosthesis researchers and technology developers in understanding the concept of embodiment and selecting metrics to assess embodiment in their research. Advances in the ability to measure the embodiment of prosthetic devices have far-reaching implications in the improvement of prosthetic limbs as well as promoting a broader understanding of ourselves as embodied agents.

Use-dependent increase in attention to the prosthetic foot in patients with lower limb amputation

Patients with lower limb amputation experience “embodiment” while using a prosthesis, perceiving it as part of their body. Humans control their biological body parts and receive appropriate information by directing attention toward them, which is called body-specific attention. This study investigated whether patients with lower limb amputation similarly direct attention to prosthetic limbs. The participants were 11 patients with lower limb amputation who started training to walk with a prosthesis. Attention to the prosthetic foot was measured longitudinally by a visual detection task. In the initial stage of walking rehabilitation, the index of attention to the prosthetic foot was lower than that to the healthy foot. In the final stage, however, there was no significant difference between the two indexes of attention. Correlation analysis revealed that the longer the duration of prosthetic foot use, the greater the attention directed toward it. These findings indicate that using a prosthesis focuses attention akin to that of an individual’s biological limb. Moreover, they expressed that the prosthesis felt like a part of their body when they could walk independently. These findings suggest that the use of prostheses causes integration of visual information and movement about the prosthesis, resulting in its subjective embodiment.

A multi-dimensional framework for prosthetic embodiment: a perspective for translational research

The concept of embodiment has gained widespread popularity within prosthetics research. Embodiment has been claimed to be an indicator of the efficacy of sensory feedback and control strategies. Moreover, it has even been claimed to be necessary for prosthesis acceptance, albeit unfoundedly. Despite the popularity of the term, an actual consensus on how prosthetic embodiment should be used in an experimental framework has yet to be reached. The lack of consensus is in part due to terminological ambiguity and the lack of an exact definition of prosthetic embodiment itself. In a review published parallel to this article, we summarized the definitions of embodiment used in prosthetics literature and concluded that treating prosthetic embodiment as a combination of ownership and agency allows for embodiment to be quantified, and thus useful in translational research. Here, we review the potential mechanisms that give rise to ownership and agency considering temporal, spatial, and anatomical constraints. We then use this to propose a multi-dimensional framework where prosthetic embodiment arises within a spectrum dependent on the integration of volition and multi-sensory information as demanded by the degree of interaction with the environment. This framework allows for the different experimental paradigms on sensory feedback and prosthetic control to be placed in a common perspective. By considering that embodiment lays along a spectrum tied to the interactions with the environment, one can conclude that the embodiment of prosthetic devices should be assessed while operating in environments as close to daily life as possible for it to become relevant.

A review of user needs to drive the development of lower limb prostheses

Background

The development of bionic legs has seen substantial improvements in the past years but people with lower-limb amputation still suffer from impairments in mobility (e.g., altered balance and gait control) due to significant limitations of the contemporary prostheses. Approaching the problem from a human-centered perspective by focusing on user-specific needs can allow identifying critical improvements that can increase the quality of life. While there are several reviews of user needs regarding upper limb prostheses, a comprehensive summary of such needs for those affected by lower limb loss does not exist.

Methods

We have conducted a systematic review of the literature to extract important needs of the users of lower-limb prostheses. The review included 56 articles in which a need (desire, wish) was reported explicitly by the recruited people with lower limb amputation (N = 8149).

Results

An exhaustive list of user needs was collected and subdivided into functional, psychological, cognitive, ergonomics, and other domain. Where appropriate, we have also briefly discussed the developments in prosthetic devices that are related to or could have an impact on those needs. In summary, the users would like to lead an independent life and reintegrate into society by coming back to work and participating in social and leisure activities. Efficient, versatile, and stable gait, but also support to other activities (e.g., sit to stand), contribute to safety and confidence, while appearance and comfort are important for the body image. However, the relation between specific needs, objective measures of performance, and overall satisfaction and quality of life is still an open question.

Conclusions

Identifying user needs is a critical step for the development of new generation lower limb prostheses that aim to improve the quality of life of their users. However, this is not a simple task, as the needs interact with each other and depend on multiple factors (e.g., mobility level, age, gender), while evolving in time with the use of the device. Hence, novel assessment methods are required that can evaluate the impact of the system from a holistic perspective, capturing objective outcomes but also overall user experience and satisfaction in the relevant environment (daily life).

Cognitive benefits of using non-invasive compared to implantable neural feedback

A non-optimal prosthesis integration into an amputee’s body schema suggests some important functional and health consequences after lower limb amputation. These include low perception of a prosthesis as a part of the body, experiencing it as heavier than the natural limb, and cognitively exhausting use for users. Invasive approaches, exploiting the surgical implantation of electrodes in residual nerves, improved prosthesis integration by restoring natural and somatotopic sensory feedback in transfemoral amputees. A non-invasive alternative that avoids surgery would reduce costs and shorten certification time, significantly increasing the adoption of such systems. To explore this possibility, we compared results from a non-invasive, electro-cutaneous stimulation system to outcomes observed with the use of implants in above the knee amputees. This non-invasive solution was tested in transfemoral amputees through evaluation of their ability to perceive and recognize touch intensity and locations, or movements of a prosthesis, and its cognitive integration (through dual task performance and perceived prosthesis weight). While this managed to evoke the perception of different locations on the artificial foot, and closures of the leg, it was less performant than invasive solutions. Non-invasive stimulation induced similar improvements in dual motor and cognitive tasks compared to neural feedback. On the other hand, results demonstrate that remapped, evoked sensations are less informative and intuitive than the neural evoked somatotopic sensations. The device therefore fails to improve prosthesis embodiment together with its associated weight perception. This preliminary evaluation meaningfully highlights the drawbacks of non-invasive systems, but also demonstrates benefits when performing multiple tasks at once. Importantly, the improved dual task performance is consistent with invasive devices, taking steps towards the expedited development of a certified device for widespread use.

Coordination Between Partial Robotic Exoskeletons and Human Gait: A Comprehensive Review on Control Strategies

Lower-limb robotic exoskeletons have become powerful tools to assist or rehabilitate the gait of subjects with impaired walking, even when they are designed to act only partially over the locomotor system, as in the case of unilateral or single-joint exoskeletons. These partial exoskeletons require a proper method to synchronize their assistive actions and ensure correct inter-joint coordination with the user’s gait. This review analyzes the state of the art of control strategies to coordinate the assistance provided by these partial devices with the actual gait of the wearers. We have analyzed and classified the different approaches independently of the hardware implementation, describing their basis and principles. We have also reviewed the experimental validations of these devices for impaired and unimpaired walking subjects to provide the reader with a clear view of their technology readiness level. Eventually, the current state of the art and necessary future steps in the field are summarized and discussed.

Subjective Response Measurement to Prosthesis or Device Use: Validation of the Prosthetic-Bionic Paradigm Questionnaire (PBP-Q)

Many subjects with somatic pathologies or traumas in their recent anamnesis tend to experience symptoms and changes to their daily life parameters after technically successful treatment. Hence, this study aims to validate an investigation tool inspired by the prosthetic-bionic paradigm-namely, the PBP-Q-which allows for the evaluation of variation in questions relating to identity, psychosociality, and psychopathology in relation to the use of a prosthesis or device. We gathered 118 participants (68 females and 50 males) aged between 27 and 94 years (Mean = 58.42 ± 15.17). We performed both exploratory (EFA) and confirmatory (CFA) factor analyses on this sample. Moreover, we calculated the internal consistency for the PBP-Q scales and the total score for the questionnaire's final 26-item and 5-factor versions. The five scales are psychological well-being; interpersonal relationships; professional relationships; autonomy and safety; addictions, compulsions, and obsessions. The internal consistency is good for both the total score and the subscales. In conclusion, overall, the PBP-Q has satisfactory psychometric properties, especially considering the measure's complexity. It provides a quick and effective way to evaluate the changes that might arise after the use of a prosthesis or device and, subsequently, has implications for clinical practice.

Perspective Taking and Avatar-Self Merging

Today, avatars often represent users in digital worlds such as in video games or workplace applications. Avatars embody the user and perform their actions in these artificial environments. As a result, users sometimes develop the feeling that their self merges with their avatar. The user realizes that they are the avatar, but the avatar is also the user-meaning that avatar's appearance, character, and actions also affect their self. In the present paper, we first introduce the event-coding approach of the self and then argue based on the reviewed literature on human-avatar interaction that a self-controlled avatar can lead to avatar-self merging: the user sets their own goals in the virtual environment, plans and executes the avatar's actions, and compares the predicted with the actual motion outcomes of the avatar. This makes the user feel body ownership and agency over the avatar's action. Following the event-coding account, avatar-self merging should not be seen as an all-or-nothing process, but rather as a continuous process to which various factors contribute, including successfully taking the perspective of the avatar. Against this background, we discuss affective, cognitive, and visuo-spatial perspective taking of the avatar. As evidence for avatar-self merging, we present findings showing that when users take the avatar's perspective, they can show spontaneous behavioral tendencies that run counter to their own.

Mind over matter: Perceived phantom/prosthesis co-location contributes to prosthesis embodiment in lower limb amputees

Prosthesis embodiment - the cognitive integration of a prosthesis into an amputees' body representation - has been identified as important for prosthetic rehabilitation. However, the underlying cognitive mechanisms remain unclear. There is reason to assume that phantom limbs that are experienced as part of the bodily self (phantom self-consciousness) can affect prosthesis embodiment, but only if the phantom and the prosthesis can be brought into perceived co-location (phantom prosthesis tolerance, PPT). In the present study, phantom-prosthesis interactions were examined in lower limb amputees, and a PPT component was psychometrically extracted. Mediation analysis revealed an indirect-only effect, where the relationship between phantom self-consciousness and prosthesis embodiment was mediated by PPT, indicating that phantom limbs can transfer their immanent vividness to the prosthesis. Subsequent analyses suggested that this effect can compensate for negative consequences on prosthesis embodiment that arise from phantom limb awareness. These results shape theoretical considerations about the cognitive processes contributing to the bodily self.

Cognitive Models of Limb Embodiment in Structurally Varying Bodies: A Theoretical Perspective

Using the seminal rubber hand illusion and related paradigms, the last two decades unveiled the multisensory mechanisms underlying the sense of limb embodiment, that is, the cognitive integration of an artificial limb into one's body representation. Since also individuals with amputations can be induced to embody an artificial limb by multimodal sensory stimulation, it can be assumed that the involved computational mechanisms are universal and independent of the perceiver's physical integrity. This is anything but trivial, since experimentally induced embodiment has been related to the embodiment of prostheses in limb amputees, representing a crucial rehabilitative goal with clinical implications. However, until now there is no unified theoretical framework to explain limb embodiment in structurally varying bodies. In the present work, we suggest extensions of the existing Bayesian models on limb embodiment in normally-limbed persons in order to apply them to the specific situation in limb amputees lacking the limb as physical effector. We propose that adjusted weighting of included parameters of a unified modeling framework, rather than qualitatively different model structures for normally-limbed and amputated individuals, is capable of explaining embodiment in structurally varying bodies. Differences in the spatial representation of the close environment (peripersonal space) and the limb (phantom limb awareness) as well as sensorimotor learning processes associated with limb loss and the use of prostheses might be crucial modulators for embodiment of artificial limbs in individuals with limb amputation. We will discuss implications of our extended Bayesian model for basic research and clinical contexts.

Factors Associated With Prosthesis Embodiment and Its Importance for Prosthetic Satisfaction in Lower Limb Amputees

Perceptual integration of a prosthesis into an amputee's body representation, that is, prosthesis embodiment, has been proposed to be a major goal of prosthetic treatment, potentially contributing to the user's satisfaction with the device. However, insufficient knowledge about individual or prosthetic factors associated with prosthesis embodiment challenges basic as well as rehabilitation research. In the present study, hierarchical multiple regression analyses on prosthesis embodiment—as assessed with the recently introduced Prosthesis Embodiment Scale—were applied to the survey data of a large sample of prosthesis-using lower limb amputees, entering relevant objective-descriptive (i.e., unbiased characteristics of the amputation or the prosthesis) and subjective-evaluative variables (i.e., the amputee's perceptions related to the amputation or the prosthesis) as first- or second-level regressors, respectively. Significant regressors identified in these analyses together explained R² = 36.3% of prosthesis embodiment variance in the present sample, with a lower level of amputation, less intense residual limb pain, more realistic visual appearance of the device, higher prosthetic mobility, and more positive valence of prosthesis-induced residual limb stimulations representing significantly associated factors. Using the identical set of regressors hierarchically complemented by prosthesis embodiment on measures of prosthetic satisfaction—as assessed with the Trinity Amputation and Prosthesis Experience Scales—revealed that prosthesis embodiment was significantly and positively associated with aesthetic as well as functional prosthesis satisfaction. These findings emphasize the importance of psychological factors for the integration of a prosthesis into the amputee's body representation, which itself represents a crucial factor associated with prosthesis satisfaction. The results might have important implications for future prosthetic treatment; however, replication of the findings in an independent sample is required, as well as sophisticated experimental designs in order to elucidate the causality of effects.

Prosthesis embodiment and attenuation of prosthetic touch in upper limb amputees - A proof-of-concept study

Sensory attenuation of self-touch, that is, the perceptual reduction of self-generated tactile stimuli, is considered a neurocognitive basis for self-other distinction. However, whether this effect can also be found in upper limb amputees using a prosthesis is unknown. Thirteen participants were asked to touch their foot sole with a) their intact hand (self-touch), b) their prosthesis (prosthesis-touch), or c) let it be touched by another person (other-touch). Intensity of touch was assessed with a questionnaire. In addition, prosthesis embodiment was assessed in nine participants. Self-touch as well as prosthesis-touch was characterized by significant perceptual attenuation compared to other-touch, while self- and prosthesis-touch did not differ. The more embodied the prosthesis was, the more similar was its elicited touch perception to actual self-touch. These findings - although preliminary - suggest that perceptually embodied prostheses can be represented as an actual limb by the users' sensorimotor system.

Talking with Your (Artificial) Hands: Communicative Hand Gestures as an Implicit Measure of Embodiment

When people talk, they move their hands to enhance meaning. Using accelerometry, we measured whether people spontaneously use their artificial limbs (prostheses) to gesture, and whether this behavior relates to everyday prosthesis use and perceived embodiment. Perhaps surprisingly, one- and two-handed participants did not differ in the number of gestures they produced in gesture-facilitating tasks. However, they did differ in their gesture profile. One-handers performed more, and bigger, gesture movements with their intact hand relative to their prosthesis. Importantly, one-handers who gestured more similarly to their two-handed counterparts also used their prosthesis more in everyday life. Although collectively one-handers only marginally agreed that their prosthesis feels like a body part, one-handers who reported they embody their prosthesis also showed greater prosthesis use for communication and daily function. Our findings provide the first empirical link between everyday prosthesis use habits and perceived embodiment and a novel means for implicitly indexing embodiment.