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

Abstract

The phenomenon of sensory attenuation, that is, the perceptual reduction of intensity for self-generated stimuli, is considered a neurocognitive basis for self-other distinction. Corroboratory, such perceptual attenuation has been shown to be dependent on the sense of embodiment, that is, the perceptual incorporation of an object or body part into one’s body representation. In the present study, we tested whether this relationship is transferrable to unilateral upper limb amputees using a prosthesis. 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 by the recently introduced Prosthesis Embodiment Scale in nine participants. We found that both 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. By calculating an index reflecting how similar prosthesis-touch was to self- or other touch and correlating this index with perceived prosthesis embodiment, we found that the more embodied the prosthesis was, the more similar was its elicited touch perception to actual self-touch. This association was specific for prosthesis embodiment, since neither prosthesis satisfaction nor prosthesis adjustment showed a similar relationship. These findings are further evidence that perceptually embodied prostheses can be represented as an actual limb by the users’ sensorimotor system, which might have important implications for future prosthetic rehabilitation.

Factors associated with prosthesis embodiment and its importance for prosthetic satisfaction in lower limb amputees

“…The present results complement previous findings by providing suggestions as to which factors are associated with prosthesis embodiment, which might guide future prosthetic developments. It has to be noted that some of the present results (e.g., the positive association between level of amputation and prosthesis embodiment) support previous studies, while others do not (e.g., the non-significant association between time since amputation and prosthesis embodiment; cf., Bekrater-Bodmann et al, 2020). This might be due to the fact that the earlier study assessed only a subcomponent of prosthesis embodiment (i.e., ownership; cf., Longo et al, 2008), while the PEmbS-LLA assesses prosthesis embodiment multidimensionally.…”

“…A recent systematic review on factors associated with prosthesis satisfaction in lower limb amputees (Baars et al, 2018) identified appearance, fit, and use of the prosthesis, medical issues of the residual limb, as well as properties of the device as important influencing factors, with sex, etiology of amputation, bedding of the residual limb in the prosthesis socket, and the level of amputation representing crucial modulating variables. Further, Bekrater-Bodmann et al (2020) found that a younger age, a longer residual limb, an increased amount of time since amputation, a higher frequency of prosthesis use, and the type of prosthesis (modular vs exoskeletal) were associated with higher prosthesis ownership -representing a sub component of embodiment (Longo et al, 2008) -in a sample of more than 1,300 lower limb amputees. Phantom and residual limb sensations have further been related to prosthesis embodiment (Giummarra et al, 2010;Kern et al, 2009;Bekrater-Bodmann et al, 2020).…”

“…Further, Bekrater-Bodmann et al (2020) found that a younger age, a longer residual limb, an increased amount of time since amputation, a higher frequency of prosthesis use, and the type of prosthesis (modular vs exoskeletal) were associated with higher prosthesis ownership -representing a sub component of embodiment (Longo et al, 2008) -in a sample of more than 1,300 lower limb amputees. Phantom and residual limb sensations have further been related to prosthesis embodiment (Giummarra et al, 2010;Kern et al, 2009;Bekrater-Bodmann et al, 2020). Most of these variables can be categorized as being related to the amputation or the prosthesis, and can further be described as being impartial (i.e., objective characteristics of the amputation or the prosthesis) or subjectiveevaluative features (i.e., the amputee's perceptions related to the amputation or the prosthesis).…”

“…Further, participants were asked how often they use the prosthesis a) per week (1 -less than twice; 2every second day; 3 -almost daily; 4 -daily) and b) per day (1 -one to two hours; 2 -several hours, but not throughout; 3 -half a day; 4 -from morning to evening). By multiplying both ratings, an ordinally scaled frequency of prosthesis use index with nine ranks was obtained, ranging from rare to frequent use (cf., Bekrater-Bodmann et al, 2020). Participants were further asked whether their prosthesis cover was individualized, i.e., whether the appearance of the prosthesis was personalized.…”

“…The total score of the PEmbS-LLA was calculated by averaging all valid items (up to one missing item was allowed in the present study, which was the case in n = 4 participants; another four participants had more than one missing value or were not able to walk with their prosthesis and were thus excluded from the subsequent analyses), with higher scores indicating higher prosthesis embodiment. The Prosthesis Embodiment Scale has previously been shown to have good to excellent reliability (Bekrater-Bodmann, 2020), and results on implicit effects suggest validity of the instrument (Fritsch et al, 2020).…”