Body visual discontinuity affects feeling of ownership and skin conductance responses

Abstract

When we look at our hands we are immediately aware that they belong to us and we rarely doubt about the integrity, continuity and sense of ownership of our bodies. Here we explored whether the mere manipulation of the visual appearance of a virtual limb could influence the subjective feeling of ownership and the physiological responses (Skin Conductance Responses, SCRs) associated to a threatening stimulus approaching the virtual hand. Participants observed in first person perspective a virtual body having the right hand-forearm (i) connected by a normal wrist (Full-Limb) or a thin rigid wire connection (Wire) or (ii) disconnected because of a missing wrist (m-Wrist) or a missing wrist plus a plexiglass panel positioned between the hand and the forearm (Plexiglass). While the analysis of subjective ratings revealed that only the observation of natural full connected virtual limb elicited high levels of ownership, high amplitudes of SCRs were found also during observation of the non-natural, rigid wire connection condition. This result suggests that the conscious embodiment of an artificial limb requires a natural looking visual body appearance while implicit reactivity to threat may require physical body continuity, even non-naturally looking, that allows the implementation of protective reactions to threat.

Figure 1

(A) Participants observed in 1PP through a HMD the virtual body in the same location and posture as the physical one; (B) The visual appearances of the avatar’s right limb: from left to right: a standard full arm (Full-Limb), a limb with a thin black rigid wire connecting the forearm and the hand (Wire), a limb with a missing wrist (m-Wrist) and a limb with a missing wrist with a Plexiglass panel placed in the blank space between the hand and the forearm (Plexiglass). Virtual models were created by the authors (see Experimental Stimuli and setup for details).

Figure 2

(A) Graphs represent the subjective ratings concerning the FO over the virtual hand and Forearm for each visual appearance. The horizontal black bars are the medians, and the boxes the interquartile ranges (IQRs). The whiskers stretch to the data points that are within the minimum and maximum score; (B) Graphs represent SCRs amplitude for each experimental condition.

Figure 3. Sequence of events during Full-limb (upper) and m-Wrist condition (lower).