Are Movements Necessary for the Sense of Body Ownership? Evidence from the Rubber Hand Illusion in Pure Hemiplegic Patients

Abstract

A question still debated within cognitive neuroscience is whether signals present during actions significantly contribute to the emergence of human’s body ownership. In the present study, we aimed at answer this question by means of a neuropsychological approach. We administered the classical rubber hand illusion paradigm to a group of healthy participants and to a group of neurological patients affected by a complete left upper limb hemiplegia, but without any propriceptive/tactile deficits. The illusion strength was measured both subjectively (i.e., by a self-report questionnaire) and behaviorally (i.e., the location of one’s own hand is shifted towards the rubber hand). We aimed at examining whether, and to which extent, an enduring absence of movements related signals affects body ownership. Our results showed that patients displayed, respect to healthy participants, stronger illusory effects when the left (affected) hand was stimulated and no effects when the right (unaffected) hand was stimulated. In other words, hemiplegics had a weaker/more flexible sense of body ownership for the affected hand, but an enhanced/more rigid one for the healthy hand. Possible interpretations of such asymmetrical distribution of body ownership, as well as limits of our results, are discussed. Broadly speaking, our findings suggest that the alteration of the normal flow of signals present during movements impacts on human’s body ownership. This in turn, means that movements have a role per se in developing and maintaining a coherent body ownership.

The role of agency for perceived ownership in the virtual hand illusion

“…As compared to the classical rubber-hand setup, these three more or less continuous informational streams provide a much richer database for the computation of cross-modal contingencies. Given that these computations are considered to represent the main factor that underlies both subjective agency (Burin et al, 2015) and subjective body ownership (Armel & Ramachandran, 2003;Botvinick & Cohen, 1998), one would indeed expect that objective agency increases both subjective agency and synchrony effects. However, while objective agency clearly plays a role for subjective ownership, it is less clear whether subjective agency is relevant for subjective ownership as well.…”

“…While earlier studies tended to consider body ownership and agency as separate components of the self (see Gallagher, 2000;Jeannerod, 2003;Tsakiris et al, 2007), there is increasing evidence that these two factors interact in producing ownership illusions (Burin et al, 2015;Dummer, Picot-Annand, Neal, & Moore, 2009;Kokkinara & Slater, 2014;Ma & Hommel, 2013Tsakiris et al, 2006Tsakiris et al, , 2007. However, the relationship between sense of ownership and sense of agency is still not clear: Some studies showed greater sense of illusory ownership with greater sense of agency, some studies showed the opposite relationship between the two senses, and some studies showed no correlation at all.…”

“…For example, Burin et al (2015) found that patients with left upper limb hemiplegia display stronger illusory effects than healthy participants when the affected hand is stimulated but no effects when the unaffected hand is stimulated, and concluded that active movement plays a role for body ownership maintenance. Along the same lines, Kokkinara and Slater (2014) observed higher ownership for a virtual leg in active-movement than visuotactile-stimulation conditions.…”

“I can't tell whether it's my hand”: a pilot study of the neurophenomenology of body representation during the rubber hand illusion in trauma-related disorders

“…Following standard methods (Burin et al, 2015), the RHI paradigm consisted of a black box (60 cm×40 cm×20 cm) with a perpendicular panel dividing it in half (30 cm×40 cm×20 cm), arranged such that the patient’s real hand would be hidden and only the life-like rubber hand would be within the patient’s view. The patient wore a white cape on her body to ensure that only the rubber hand was in view and was oriented such that the patient’s shoulder was in line with the rubber hand.…”

“…The participant was then asked to report the number on the ruler that corresponded to her perceived index finger (Burin et al, 2015). This procedure was repeated six times, changing randomly the position of the ruler each time.…”