A Study on the Flexibility of Body Ownership
Date Issued
2016
Date
2016
Author(s)
Chen, Wen-Yeo
Abstract
Recent studies of the rubber hand illusion (RHI) have shown that the sense of body ownership is constrained by several factors, yet is still very flexible. In order to increase our understanding, one significant aspect to consider is exactly how flexible our sense of body ownership really is. The distinction between “body-as-subject” and “body-as-object” in phenomenology forms a theoretical constraint regarding the sense of body ownership. According to this phenomenological constraint, a subject cannot experience his/her own body or body-parts both as-subject and as-object simultaneously. In this study, this issue is addressed by investigating the following questions: (1) Is it possible to have the illusion of owning four hands? and (2)Is it possible to experience body-as-subject and body-as-object at the same time? Using a head mounted display (HMD), the participant adopted the experimenter’s first-person perspective (1PP) as if it were his/her own. Sitting face to face, the participant saw either two or four hands—the experimenter’s two hands from the adopted 1PP and/or the subject’s own two hands in the opposite direction from an adopted third-person perspective (3PP)—being stroked synchronously or asynchronously. In an active four-handed condition, the participants were asked to tap their index fingers, while the experimenter imitated their movements. The result showed that in the passive two-hand condition, synchronous touching induced a variant of the RHI. In the passive four-hand condition, subjective tactile location could be dissociated from the sense of hand ownership. Strikingly, in the active condition, once all four hands began to act in the same pattern synchronously, many participants (68%) agreed or strongly agreed with the statement “I felt as if I had two more hands.” Supported by skin conductance response (SCR) measurements, these results show that the sense of body ownership is much more flexible than what most research has previously suggested. I investigate the “neurocognitive model of body ownership” proposed by Tsakiris (2010) in light of this study and argue that his model should be complemented by the involvement of the sense of agency and visual perspective, which were neglected completely in the previous model. Furthermore, a key component of the four-hand illusion provides an important counter-example against the distinction between body-as-object and body-as-subject. I try to show that it is possible for healthy participant to experience both body-as-subject and for body-as-object simultaneously. This behavioral study showed for the first time that it is possible to induce a “four-hand illusion” with healthy participants. Based on this result, further neuroscientific research is needed to discover the neural mechanism underpinning the sense of body ownership. I suggest that investigating Task-related functional connectivity will help determine the neural basis that underlies the relationship between a sense of body ownership and a sense of agency.
Subjects
Four-hand illusion
self-consciousness
Sense of body ownership
sense of agency
body-as-subject
body-as-object
Type
thesis
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