Abstract
Recent studies have shown that a fake body part can be incorporated into human body representation through synchronous multisensory stimulation on the fake and corresponding real body part – the most famous example being the Rubber Hand Illusion. However, the extent to which gross asymmetries in the fake body can be assimilated remains unknown. Participants experienced, through a head-tracked stereo head-mounted display a virtual body coincident with their real body. There were 5 conditions in a between-groups experiment, with 10 participants per condition. In all conditions there was visuo-motor congruence between the real and virtual dominant arm. In an Incongruent condition (I), where the virtual arm length was equal to the real length, there was visuo-tactile incongruence. In four Congruent conditions there was visuo-tactile congruence, but the virtual arm lengths were either equal to (C1), double (C2), triple (C3) or quadruple (C4) the real ones. Questionnaire scores and defensive withdrawal movements in response to a threat showed that the overall level of ownership was high in both C1 and I, and there was no significant difference between these conditions. Additionally, participants experienced ownership over the virtual arm up to three times the length of the real one, and less strongly at four times the length. The illusion did decline, however, with the length of the virtual arm. In the C2–C4 conditions although a measure of proprioceptive drift positively correlated with virtual arm length, there was no correlation between the drift and ownership of the virtual arm, suggesting different underlying mechanisms between ownership and drift. Overall, these findings extend and enrich previous results that multisensory and sensorimotor information can reconstruct our perception of the body shape, size and symmetry even when this is not consistent with normal body proportions.
Highlights
Body ownership refers to the attribution of objects as being part of one’s own body [1,2,3]
In this paper we show that it is possible to quite dramatically alter body representation, by inducing an ownership illusion over one very long arm in a situation where the entire body has been replaced by a virtual body seen from a first person perspective position (1PP)
The difference between the participants’ estimations before and after the stimulation is called ‘proprioceptive drift’ and it is widely considered as a behavioral correlate of the ownership illusion, a recent study [10] challenged the idea that there is a common underlying mechanism that connects drift with the subjective illusion of ownership
Summary
Body ownership refers to the attribution of objects (e.g. limbs) as being part of one’s own body [1,2,3]. In the rubber hand illusion (RHI), synchronous visual stimulation of a rubber hand (placed in an anatomically plausible position on a table) and corresponding tactile stimulation of the hidden real hand induces the illusory feeling the rubber hand is part of the body representation [7,8]. Under this illusory perception, participants when asked to localize their real hand they are more likely to point closer to the rubber hand after the stimulation compared to before [7,9]. It has been proposed that the artificial body part should obey various morphological, anatomical and postural constraints (for a review see [6]) including the necessity for human body part resemblance
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