The contribution of stimulating multiple body parts simultaneously to the illusion of owning an entire artificial body

Abstract

8The full-body ownership illusion exploits multisensory perception to induce a feeling of ownership for an 9 entire artificial body. Whilst previous research has shown that the synchronous visuotactile stimulation of a single 10 body part is sufficient for illusory ownership over the whole body, the effect of combining multisensory stimulation 11 across multiple body parts remains unknown. Therefore, 48 healthy adults participated in conditions of a full-12 body ownership illusion involving synchronous or asynchronous visuotactile stimulation to one, two or three body 13 parts simultaneously (2 x 3 design). We developed a novel questionnaire to isolate the sense of ownership of 14 five specific body parts (left leg, right leg, left arm, right arm, and trunk) from the full-body ownership experience 15 and sought not only to test for greater (part and whole) body ownership in synchronous versus asynchronous 16 stimulation, but also, potentially varying degrees of illusion intensity related to the number of body parts 17 stimulated. As expected, illusory full-body ownership and all five body-part ownership ratings were significantly 18 higher following synchronous stimulation (all p values ≤ .01). Since non-stimulated body parts also received 19 significantly higher ownership ratings following synchronous stimulation, the results are consistent with an illusion 20 engaging the entire body. We further noted that ownership ratings for the right body parts (often stimulated) were 21 significantly higher than ownership ratings for the left body parts (never stimulated). Regarding explicit feelings 22 of full-body ownership, subjective ratings were not significantly enhanced by increasing the number of 23 synchronously stimulated body parts (synchronicity x number stimulated interaction; p .099). Instead, median 24 ratings indicated a moderate affirmation (+1) of full-body illusory sensation for all three synchronous conditions; 25 a finding mirrored by full-body illusion onset time. The results support the notion that feelings of full-body 26 ownership are mediated by a generalisation from stimulated part(s)-to-whole, supported by processes related to 27 multisensory body perception.

Bodily ownership and agency sensations in a natural state

“…Similar bodily illusions have also been reported for a foot 11 and face 12 . Visuo-tactile synchronous stimulations to a single body part was also reported to induce the illusory ownership sensation of whole body to a body-like object 13 – 18 .…”

“…Thus, the findings obtained from experimental studies may not directly apply to understanding how our bodily sensations are maintained in a natural, ecologically valid manner. Additionally, most experimental studies so far has also focused on a single body part or on the whole body but see 15 , 18 . This may be because the sensations of a single body part, such as the hands, are easy to temporally manipulate, in addition to the fact that experimental manipulations usually take several minutes to induce bodily illusions.…”