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.

Visual appearance of a virtual upper limb modulates the temperature of the real hand: a thermal imaging study in Immersive Virtual Reality

“…In the Calibration phase, the avatar's size and the point‐of‐view of each participant were adjusted to accord with individual dimensions and positioning. In the Familiarisation phase, participants were invited to look both at the virtual body (which was fully visible in 1PP, without any occlusion over the left upper limb by the virtual grey panel) and at the environment, and to verbally describe what they were seeing (60 s) (Slater et al ., ; Tieri et al ., 2015b).…”

“…Recent advances in computer science have allowed researchers to use Immersive Virtual Reality (IVR) to investigate the SoE over a virtual body by adapting the original version of the RHI paradigm. Data obtained regarding embodiment of virtual body parts (Slater et al ., , ; Sanchez‐Vives et al ., ) and full virtual bodies (Ehrsson, ; Lenggenhager et al ., ; Petkova & Ehrsson, ; Slater et al ., ; Maselli & Slater, , ) show that first‐person perspective (1PP) and visual appearance of the virtual body (Kilteni et al ., ; Perez‐Marcos et al ., ; Martini et al ., ; Tieri et al ., ,b) have crucial roles in eliciting SoE (Petkova & Ehrsson, ; Petkova et al ., ; Slater et al ., ; Maselli & Slater, ). Similarly, we recently reported that even the mere passive observation of a virtual limb from a 1PP (without any multisensory visuo‐tactile or visuo‐motor boosting) is sufficient to elicit FO at explicit (e.g., questionnaire answers; Tieri et al ., 2015a), implicit [e.g.…”

“…Similarly, we recently reported that even the mere passive observation of a virtual limb from a 1PP (without any multisensory visuo‐tactile or visuo‐motor boosting) is sufficient to elicit FO at explicit (e.g., questionnaire answers; Tieri et al ., 2015a), implicit [e.g. skin conductance response (SCR; Tieri et al ., 2015b; Fusaro et al ., ) and electroencephalographic response (Pavone et al ., )] levels. Moreover, we observed (Tieri et al ., 2015a) that 1PP passive observation can also induce a feeling of control over the virtual body's actions (i.e.…”

“…Vicarious Agency (VA); Wegner et al ., ). Relevant to the present study, we found that both subjective ratings (Tieri et al ., ,b) and amplitude of SCRs (Tieri et al ., 2015b) were lowered when the virtual hand appeared to be disconnected from the rest of the body. This suggests the importance of body visual continuity in eliciting SoE.…”

“…Moreover, since heart rate (HR) may be an index of general autonomic reactivity (Bradley & Lang, ; Kreibig, ) rather than a proxy to embodiment (Fusaro et al ., ) and presence (Vecchiato et al ., ), we recorded it as a control measure. Based on previous evidence that (i) the illusory SoE is reflected by a drop in skin temperature of the real hand (Moseley et al ., ) and (ii) the observation of a virtual body in 1PP is sufficient to elicit SoE (Petkova & Ehrsson, ; Slater et al ., ; Petkova et al ., ; Maselli & Slater, ; Tieri et al ., ,b; Pavone et al ., ), we expected maximal subjective ratings of SoE (FO and VA) and a decrease in skin temperature during observation of the Full‐Limb condition. Moreover, we expected negative correlations between subjective ratings (FO and VA) and skin temperature for this condition.…”