Long arm illusion

We can feel as if a fake body is our own body even if the body has a different shape and color [1]. Several studies have reported that the illusory body ownership can be induced to various body shapes and colors. For example, the illusory ownership can be induced to elongated hands [2][3], and a very small body or large body [4][5]. Thus, we can have an illusory ownership of a virtual hand and arm and it can be transformed.We aimed to investigate if we can have an illusory ownership to an elongated arm using the "invisible body" paradigm, that is developed by our team [6].
In Experiment 1, we measured illusory body ownership of a visible whole body with a long arm using the subjective ratings, and measured body sway after experiencing illusory body ownership. We hypothesized that illusory body ownership is induced to the long-arm body when the hands and feet moved synchronously with the subject’s movements, and their body tilts toward the normal arm to maintain body posture. We found that the illusory body ownership could be induced to the whole visible body that had a long left/right arm and a normal right/left arm when the avatar was synchronized with participants’ movement.
In Experiment 2, we investigated whether the illusory body ownership can be induced to the invisible long arm body by presenting only hands and feet using the subjective ratings. We measured proprioceptive pointing of the hand of elongated arm. We found that the illusory body ownership to the body with a long arm was induced to an invisible body by synchronizing only gloves and socks with participants' movement.
In Experiment 3, to see the learning process of the elongated-arm body, we investigated the illusory body ownership for the invisible long arm body through measuring reaching behaviors and body sway in time series as well as the subjective ratings. We found that the behaviors of using the long arm and the normal arm to touch an object changed gradually as learning the invisible body up to 7.5 min. However, the results of postural sway and proprioceptive pointing were not consistent with our prediction.
Illusory body ownership was induced to both the long arm fully visible body and the long arm invisible body, and the length of the arm of participants felt changed. Participants' behavior gradually changed to use the longer arm more during the learning of the transformed body.


Kondo, R., Ueda, S., Sugimito, M., Minamizawa, K., Inami, M., and Kitazaki, M. (2018). Invisible long arm illusion: illusory body ownership by synchronous movement of hands and feet. ICAT-EGVE 2018, Limassol, Cyprus, November 7-9, 2018.


[1] Kilteni, K., Maselli, A., Kording, K. P., & Slater, M. (2015). Over my fake body: body ownership illusions for studying the multisensory basis of own-body perception. Frontiers in Human Neuroscience, 9, 141.
[2] Armel, K. C., & Ramachandran, V. S. (2003). Projecting sensations to external objects: evidence from skin conductance response. Proceedings of the Royal Society of London B: Biological Sciences, 270, 1499-1506.
[3] Kilteni, K., Normand, J. M., Sanchez-Vives, M. V., & Slater, M. (2012). Extending body space in immersive virtual reality: a very long arm illusion. PLoS One, 7, e40867.
[4] Van Der Hoort, B., Guterstam, A., & Ehrsson, H. H. (2011). Being Barbie: the size of one’s own body determines the perceived size of the world. PLoS One,6, e20195.
[5] Van Der Hoort, B., & Ehrsson, H. H. (2016). Illusions of having small or large invisible bodies influence visual perception of object size. Scientific Reports, 6, 34530.
[6] Kondo, R., Sugimoto, M., Minamizawa, K., Hoshi, T., Inami, M., & Kitazaki, M. (2018). Illusory body ownership of an invisible body interpolated between virtual hands and feet via visual-motor synchronicity. Scientific Reports, 8, 7541.


見えない長い腕:四肢先端の視覚運動同期による四肢伸張透明身体への所有感生成と行動変容.                   日本バーチャルリアリティ学会論文誌, 24(4), 351-360.近藤 亮太,上田祥代,杉本麻樹,南澤孝太,稲見昌彦,北崎充晃