Spatial Augmented Respiratory Cardiofeedback Design for Prosthetic Embodiment Training: a Pilot Study

Recent literature suggests that self-regulation techniques like biofeedback can be used to enhance the embodiment of artificial limbs. In this study, we developed and preliminarily tested an embodiment training protocol based on a Spatial Augmented Respiratory Cardiofeedback (SARC) implemented through a computer screen - visualizing a 3D model of a prosthetic hand (Hannes) - and a thoracic band for monitoring the Heart Rate Variability (HRV) of the users. The feedback was based on the respiratory-driven modulation of a composite index of the individuals’ cardiac autonomic state after an initial calibration based on slow breathing (at a rate perceived as “comfortable”). Alongside the assessment of the SARC use feasibility, this pilot study evaluates the virtual hand embodiment obtained in two task conditions. In both conditions, the virtual limb gradually appears when the cardiofeedback exercise is performed correctly. Otherwise, the virtual limb parts gradually disappear (“unstable” condition) or they remain visible (cumulative” condition). In the latter case, the virtual hand maintains its “reality-based” stability, supporting the subject’s motivation. Ten volunteers without disabilities were presented both conditions on 10 trials each (2min per trial). Their experience and their proprioceptive drift (estimating their real hand position as close to the artificial one) were assessed as measures of virtual prosthesis embodiment. The questionnaire results preliminarily highlight the feasibility of the SARC. Furthermore, a significantly stronger drift for the virtual prosthesis occurred in the cumulative condition, orienting further investigations.