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Sandra Truong, Regine Zopf, Matthew Finkbeiner, Jason Friedman, Mark Williams; Perceptual Body Illusion Affects Action. Journal of Vision 2010;10(7):1052. doi: 10.1167/10.7.1052.
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© ARVO (1962-2015); The Authors (2016-present)
Synchronously stimulating an artificial hand and a participant's hand that is hidden from view induces an apparent proprioceptive shift towards the artificial hand (Rubber Hand Illusion; RHI), such that participants subjectively report their hand location to be between the real and artificial hand. This effect is reduced or eliminated with asynchronous visual and somatosensory stimulation. Although previously thought of as a purely perceptual illusion, here we show that the RHI influences ballistic movements directly. A repeated measures design was used to compare participants' task performance during synchronous and asynchronous stimulation conditions. First, the RHI was induced, and then participants were asked to perform ballistic hand movements towards targets presented in a randomized location on a touch screen. A motion capture system was utilized to record hand movement trajectories for analysis. We found significantly larger reaching endpoint errors in the synchronous than asynchronous conditions. Importantly, these errors were biased to the side of the target opposite the side of the artificial hand, consistent with participants moving their hand as if position is computed to be intermediate between the real and rubber hand. It is believed that peripersonal space systems integrate multisensory information to form body-part-centered (e.g. hand-centered) maps of local space. The computation of hand position incorporates input from visual, tactile and proprioceptive modalities and a shift in any or multiple of these sensory mappings, as induced by the RHI, results in a misperception of hand location. This study suggests that the re-alignment of mappings, which is modulated by the RHI leads to direct effects in reaching biases for action and visually-based proprioceptive judgments. Importantly, these results show, beyond the limitations of subjective report of perceived hand position used in previous studies, that the RHI has a fundamental impact on motor action towards visual targets.
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