Abstract:

Body image consists of a system of perceptions, attitudes, and beliefs pertaining to one’s own. The appearance of one’s own body “from the outside”, is thought to be an important component of body image, therefore many studies focus on the visual perceptual component of body image. The controversies concerning body image are not only between nature and nurture, but also about its stability. On the one hand, body image seems to play an important role whenever we need to recognize ourselves, it is easy for us to take it as a stable representation of our body. On the other hand, the studies of amputees who experience phantom limbs suggested a sense that one’s body image is itself a “phantom”, so it is also reasonable to think body image as something that is at least plastic. The rubber hand illusion (RHI) paradigm seems to be one of the appropriate ways to investigate this controversy about body image, since it could induce the experience of an artificial body part as becoming a real body part among normal people. This illusion was first reported by Botvinick and Cohen who placed a rubber hand in front of participants whose corresponding real hand was hidden from sight. When the real hand and the visible rubber hand were stroked in a synchronous fashion, participants reported to experience the rubber hand as being a part of their body. Studies concerning the factors affect the induction or reduction of RHI suggested that the RHI depends not only on synchronous stimulations, but also on the match between the rubber hand and pre-existing body images. However, till now, no studies have combined top-down and bottom-up to seek the answer for the plasticity of body image. In the present study, we adopted distance reference as a new factor to investigate the plasticity of body image. Our study included two experiments both of which were performed in a virtual environment. In the first experiment, we simulated the traditional rubber hand illusion to determine the influences of synchronicity and location on bodily sense of ownership in our setups. It was a 2-factorial between-participants design. The two factors were synchronicity (synchronous vs. asynchronous) and distance (near vs. far). In the second experiment, we introduced distance reference frame to investigate how participants felt differently about the virtual hand in the same location, while there were different distance reference frames. There were two between-participants factors: synchronicity (synchronous vs. asynchronous) and distance reference frame (near-middle vs. far-middle). The near-middle reference frame was: participants experienced the middle position condition right after the near position condition; while the far-middle reference frame was: participants experienced the middle position condition right after the far position condition. The following results and conclusions were found by our study: (1) under normal situations, synchronicity and distance played an important role on our perception of ownership. People perceived more ownership whenever there were synchronous visuo-tactile stimulations than asynchronous ones, and also, more ownership when the virtual hand was right in front of them than in an anatomical impossible position. (2) Distance reference frame influenced peoples’ perception on their own body, the size of the ownership illusion varied as a function of relative, rather than absolute location of the virtual hand. Our result suggests a considerable degree plasticity of body image underlying our body ownership.

Key words: rubber hand illusion, virtual hand illusion, body image, distance reference frame, sense of ownership