Abstract
Previous research has shown that it is possible to use multisensory stimulation to induce the perceptual illusion of owning supernumerary limbs, such as two right arms. However, it remains unclear whether the coherent feeling of owning a full-body may be duplicated in the same manner and whether such a dual full-body illusion could be used to split the unitary sense of self-location into two. Here, we examined whether healthy human participants can experience simultaneous ownership of two full-bodies, located either close in parallel or in two separate spatial locations. A previously described full-body illusion, based on visuo-tactile stimulation of an artificial body viewed from the first-person perspective (1PP) via head-mounted displays, was adapted to a dual-body setting and quantified in five experiments using questionnaires, a behavioural self-location task and threat-evoked skin conductance responses. The results of experiments 1–3 showed that synchronous visuo-tactile stimulation of two bodies viewed from the 1PP lying in parallel next to each other induced a significant illusion of dual full-body ownership. In experiment 4, we failed to find support for our working hypothesis that splitting the visual scene into two, so that each of the two illusory bodies was placed in distinct spatial environments, would lead to dual self-location. In a final exploratory experiment (no. 5), we found preliminary support for an illusion of dual self-location and dual body ownership by using dynamic changes between the 1PPs of two artificial bodies and/or a common third-person perspective in the ceiling of the testing room. These findings suggest that healthy people, under certain conditions of multisensory perceptual ambiguity, may experience dual body ownership and dual self-location. These findings suggest that the coherent sense of the bodily self located at a single place in space is the result of an active and dynamic perceptual integration process.
Highlights
Previous research has shown that it is possible to use multisensory stimulation to induce the perceptual illusion of owning supernumerary limbs, such as two right arms
In support of our first hypothesis, we found that synchronous visuo-tactile stimulation of the participants’ body and two virtual bodies viewed from the 1PP, placed in close proximity side-by-side, elicited a strong sense of dual full-body ownership, supported by the questionnaire and threat-evoked SCR measurements
This finding extends earlier work on supernumerary limb illusions to the case of experiencing ownership over two entire bodies viewed side-by-side from the 1PP and suggests that the perceived oneness of the bodily self is the result of active multisensory integration processes
Summary
Previous research has shown that it is possible to use multisensory stimulation to induce the perceptual illusion of owning supernumerary limbs, such as two right arms. The study did not quantify ownership and self-location with any established behavioural (e.g. proprioceptive drift [21]) or physiological measurement (e.g. threatevoked skin conductance responses (SCRs) [22]) This preliminary observation indicates that the healthy human brain has the capacity to represent dual self-location, it is unclear whether a dual full-body ownership illusion was induced and whether this visuo-movement approach can be used to manipulate ownership and self-location in a predictable manner. The first goal was to test the hypothesis that it is possible to elicit an illusion of owning two full-bodies by applying congruent visuo-tactile stimulation of two artificial bodies presented side-by-side and viewed from the first-person perspective (1PP) (experiments 1–3) This hypothesis was based on previous work on full-body illusions using single bodies [15,16,17,18] and studies on supernumerary limb illusions [11,12,13,14]. Illusory dual-body ownership was quantified using questionnaires [10] (experiment 1) and threat-evoked SCRs [13,22,28,29,30,31,32] (experiments 2 and 3)
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