Challenging the Boundaries of the Physical Self: Distal Cues Impact Body Ownership.

Klaudia Grechuta,Belén Rubio Ballester,Paul Verschure,Javier De La Torre Costa

doi:10.3389/fnhum.2021.704414

Abstract

The unique ability to identify one’s own body and experience it as one’s own is fundamental in goal-oriented behavior and survival. However, the mechanisms underlying the so-called body ownership are yet not fully understood. Evidence based on Rubber Hand Illusion (RHI) paradigms has demonstrated that body ownership is a product of reception and integration of self and externally generated multisensory information, feedforward and feedback processing of sensorimotor signals, and prior knowledge about the body. Crucially, however, these designs commonly involve the processing of proximal modalities while the contribution of distal sensory signals to the experience of ownership remains elusive. Here we propose that, like any robust percept, body ownership depends on the integration and prediction across all sensory modalities, including distal sensory signals pertaining to the environment. To test our hypothesis, we created an embodied goal-oriented Virtual Air Hockey Task, in which participants were to hit a virtual puck into a goal. In two conditions, we manipulated the congruency of distal multisensory cues (auditory and visual) while preserving proximal and action-driven signals entirely predictable. Compared to a fully congruent condition, our results revealed a significant decrease on three dimensions of ownership evaluation when distal signals were incongruent, including the subjective report as well as physiological and kinematic responses to an unexpected threat. Together, these findings support the notion that the way we represent our body is contingent upon all the sensory stimuli, including distal and action-independent signals. The present data extend the current framework of body ownership and may also find applications in rehabilitation scenarios.

Highlights

The sense of body ownership, which allows us to determine the boundaries between the own physical self and the external world, and the source of a given sensation, is fundamental in adaptive goal-oriented behavior and survival (Engel et al, 2001; Tsakiris et al, 2006a; Tsakiris, 2010; Kilteni and Ehrsson, 2017)
Their experiment revealed that a mere expectation of an upcoming sensory event, predicted by an anticipatory response in multisensory parietal cortices, is sufficient to induce the experience of ownership over a rubber hand, measured subjectively and objectively (Ferri et al, 2013, 2017). This finding supports the notion that body ownership can emerge as a result of the pure expectation of correlated multisensory inputs, which challenges the originally defined necessary conditions of the embodiment discussed above (Tsakiris, 2010). We extend this hypothesis and propose that, like any coherent percept, body ownership is a result of bottom-up integration and top-down prediction of all the sensory stimuli processed by, interoceptive and exteroceptive, proximal and distal modalities including those which pertain to the environment
The significant differences (Mann-Whitney U) found in the evaluated ownership dimensions and the effect sizes found for these metrics suggest that the incongruencies in distal sensory modalities influenced the experience of body ownership for the virtual avatar in the experimental as compared to the control condition

Summary

Introduction

The sense of body ownership, which allows us to determine the boundaries between the own physical self and the external world, and the source of a given sensation, is fundamental in adaptive goal-oriented behavior and survival (Engel et al, 2001; Tsakiris et al, 2006a; Tsakiris, 2010; Kilteni and Ehrsson, 2017). In mRHI, the visual feedback of voluntary arm or finger movements is either synchronized with the actual trajectory or not, biasing the experience of ownership over the virtual body (Tsakiris et al, 2006b; Dummer et al, 2009; Sanchez-Vives et al, 2010; Kalckert and Ehrsson, 2012) Both in the RHI and mRHI or their variations, one of the sensory signals manipulated to induce the experience of ownership always involves the processing of a proximal modality, which requires an object to enter in direct contact with the surface of the body, such as touch or proprioception (Botvinick and Cohen, 1998; SanchezVives et al, 2010). Within the current body ownership framework their role remains elusive

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Discussion

Conclusion