Exploring the Embodiment of a Virtual Hand in a Spatially Augmented Respiratory Biofeedback Setting

Abstract

Enhancing the embodiment of artificial limbs—the individuals' feeling that a virtual or robotic limb is integrated in their own body scheme—is an impactful strategy for improving prosthetic technology acceptance and human-machine interaction. Most studies so far focused on visuo-tactile strategies to empower the embodiment processes. However, novel approaches could emerge from self-regulation techniques able to change the psychophysiological conditions of an individual. Accordingly, this pilot study investigates the effects of a self-regulated breathing exercise on the processes of body ownership underlying the embodiment of a virtual right hand within a Spatially Augmented Respiratory Biofeedback (SARB) setting. This investigation also aims at evaluating the feasibility of the breathing exercise enabled by a low-cost SARB implementation designed for upcoming remote studies (a need emerged during the COVID-19 pandemic). Twenty-two subjects without impairments, and two transradial prosthesis users for a preparatory test, were asked (in each condition of a within-group design) to maintain a normal (about 14 breaths/min) or slow (about 6 breaths/min) respiratory rate to keep a static virtual right hand “visible” on a screen. Meanwhile, a computer-generated sphere moved from left to right toward the virtual hand during each trial (1 min) of 16. If the participant's breathing rate was within the target (slow or normal) range, a visuo-tactile event was triggered by the sphere passing under the virtual hand (the subjects observed it shaking while they perceived a vibratory feedback generated by a smartphone). Our results—mainly based on questionnaire scores and proprioceptive drift—highlight that the slow breathing condition induced higher embodiment than the normal one. This preliminary study reveals the feasibility and potential of a novel psychophysiological training strategy to enhance the embodiment of artificial limbs. Future studies are needed to further investigate mechanisms, efficacy and generalizability of the SARB techniques in training a bionic limb embodiment.

Respiratory rhythm affects recalibration of body ownership

“…Given the relationship between somatosensory input and PPC, the lack of tactile stimulation in the current experiment may have resulted in less PPC involvement and, therefore, the effect of the respiratory rhythm may not have affected location sense. Unlike previous research, which examined the relation between respiratory rhythm and virtual body [20][21][22][23][24] , our result that hand location sense is less likely to cause recalibration than hand ownership sense in the real object, may be a point of caution for application to real hand or body.…”

“…In the current results, the effect size of temporal synchronization was low (η 2 = 0.027). As our RHI experiment dealt with "object in real space," it was expected to be different from the "virtual body," reported in the previous studies 20 – 24 . Compared to the transference to the virtual body, the transference to real object was weaker, which may have led to the low effect size.…”

“…Previous works have reported that respiration modulates self-awareness by using a virtual body flashing synchronously with their respiratory rhythm [20][21][22][23][24] . However, it remains unknown whether this method can transfer body perception in real space to other objects that exist in real space as well.…”

Prosthetic embodiment: systematic review on definitions, measures, and experimental paradigms

“…Understandings of embodiment as integration in body representation or as bodily aspects of human subjectivity are two sides of the same coin and some of the definitions that we have analyzed (roughly 4%, or 5 out of 125) reflect this falling under a mix of the two themes (e.g., “the individuals' feeling that a virtual or robotic limb is integrated in their own body scheme” [ 65 ]).…”

Benefits of the Cybathlon 2020 experience for a prosthetic hand user: a case study on the Hannes system

“…Indeed, this may increase the technology acceptance of the prostheses. UX depends on many factors such as the control approach used to control the prosthesis [ 5 ], interactive training methods [ 6 ], embodiment stimulation [ 7 ], and biomimetic design strategies [ 8 ]. Furthermore, the development of a prosthesis capable to induce the embodiment and to be felt as a valid and natural substitution of the missing limb by the amputee, rather than a simple tool, is an important target as well.…”