Experimentally induced limb-disownership in mixed reality

Abstract

The seemingly stable construct of our bodily self depends on the continued, successful integration of multisensory feedback about our body, rather than its purely physical composition. Accordingly, pathological disruption of such neural processing is linked to striking alterations of the bodily self, ranging from limb misidentification to disownership, and even the desire to amputate a healthy limb. While previous embodiment research has relied on experimental setups using supernumerary limbs in variants of the Rubber Hand Illusion, we here used Mixed Reality to directly manipulate the feeling of ownership for one's own, biological limb. Using a Head-Mounted Display, participants received visual feedback about their own arm, from an embodied first-person perspective. In a series of three studies, in independent cohorts, we altered embodiment by providing visuotactile feedback that could be synchronous (control condition) or asynchronous (400ms delay, Real Hand Illusion). During the illusion, participants reported a significant decrease in ownership of their own limb, along with a lowered sense of agency. Supporting the right-parietal body network, we found an increased illusion strength for the left upper limb as well as a modulation of the feeling of ownership during anodal transcranial direct current stimulation. Extending previous research, these findings demonstrate that a controlled, visuotactile conflict about one's own limb can be used to directly and systematically modulate ownershipwithout a proxy. This not only corroborates the malleability of body representation but questions its permanence. These findings warrant further exploration of combined VR and neuromodulation therapies for disorders of the bodily self.

Achronopresence: how temporal visuotactile and visuomotor mismatches modulate embodiment

“…Subjective changes in embodiment were measured with a questionnaire given to the participants after a stroking period. In line with previous studies (Gentile et al, 2013;Kannape et al, 2019) asynchronous stimulation generally reduced the feeling of embodiment, suggesting that synchronous multisensory inputs are not only crucial to induce embodiment over a supernumerary body (e.g. Botvinick & Cohen, 1998) In the case of synchronous stimulation, only two main factors were identified in the PCA, namely embodiment and disownership, together accounting for 71% of the variance (see supplementary material, Table S7).…”

“…In contrast to illusory supernumerary ownership, which has described to occur after 11 s in visuotactile rubber hand setups (Ehrsson et al, 2004), 22.8 in active visuomotor (Kalckert & Ehrsson, 2017), and 36 in a visuotactile virtual hand setups (Perez-Marcos, Sanchez-Vives, & Slater, 2012) our Experiment 2 shows that even after short periods of stimulation (7 s), it is possible to manipulate the sense of one's own body consistently and reliably (cp. also (Kannape et al, 2019). Such a procedure can be sensitive for comparing individual differences as well as between different populations.…”

“…Here we directly manipulated embodiment of one's biological hand using a controlled multisensory conflict, without the use of a proxy/rubber hand. Previous studies suggest a feeling of disownership and numbness during delayed and therefore conflicting visual feedback of a tactile event in a mixed reality setup using infrared camera feed (Kannape et al, 2019) or prerecorded video (Gentile et al, 2013). By using an online, naturally colored, and large field of view video-feed on a head mounted display (HMD), which provides a direct view on the own body in its current environment, we adapted such setups to be more realistic and thus more ecologically valid.…”

“…For two stimulation durations (1 and 3 minutes) the participant's hand was stroked with a paintbrush while the visual feedback, was either delayed (~illusion condition) or not (~control condition). Alterations in embodiment, ownership, sensations of deafferentation and related phenomenological sensations were measured using questionnaires adapted from (Botvinick & Cohen, 1998;Kannape et al, 2019;Lenggenhager et al, 2007;Longo et al, 2008). Furthermore, previously suggested implicit correlates of embodiment, namely skin temperature (see Moseley et al, 2008, but see also de Haan et al, 2017 for a critical view) and skin conductance responses (SCR) to threat (see Armel & Ramachandran, 2003) were assessed.…”

Weakening the subjective sensation of own hand ownership does not interfere with rapid finger movements

“…Furthermore, the influence of body ownership on the cortical motor system described by aforementioned experimental articles should not only have functional relevance, but should also be evident in paradigms other than the rubber hand illusion. Previous research suggests that presenting individuals with incongruent multisensory information regarding their real body can reduce the subjective sensation of ownership over the body or reduce skin conductance response to threats [48][49][50][51][52][53][54], suggesting that the real body can be both explicitly and implicitly disowned in experimental settings, without 'replacing' it with a false limb. This might provide a more pure way of examining the role of body ownership in the movement of the real body.…”