Disconnected hand avatar can be integrated into the peripersonal space
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RESEARCH ARTICLE
Disconnected hand avatar can be integrated into the peripersonal space Daisuke Mine1 · Kazuhiko Yokosawa1 Received: 12 May 2020 / Accepted: 23 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Several studies have shown that space immediately surrounding the body, or the peripersonal space is represented differently in the brain from the more distant extra-personal space. Moreover, the boundary of peripersonal space can be extended to space surrounding the tip of a tool held by the hand. However, it is not known if tools need to be connected to the body to modulate the peripersonal space. We used a line bisection task to investigate whether peripersonal space representation surrounds a virtual hand avatar that is disconnected from the body. Healthy participants conducted a line bisection task by responding with either a virtual hand avatar or a laser pointer. The to-be-bisected lines were presented either in peripersonal or extra-personal space. When the lines were placed in extra-personal space, the virtual hand avatar was presented near the line such that the hand avatar was far from participants and disconnected from their bodies. Results indicated a shift in the line bisection bias from the left to the right as the line presentation distance increased when using the laser pointer, whereas no shift in bias was observed when using the virtual hand avatar. This result indicates that objects resembling human hands presented even at a distance and disconnected from the body can be integrated into the peripersonal space, which suggests that peripersonal space representation is more flexible than previously reported. Keywords Peripersonal space · Line bisection task · Pseudoneglect · Virtual reality
Introduction Dissociation between peripersonal and extra‑personal space The peripersonal space (PPS) is the space surrounding the body in which physical interactions can occur between an individual and the environment, whereas the extra-personal space is the space far from the body. Neuropsychological, neurophysiological, and behavioral studies have shown that the brain has distinct mechanisms for coding PPS and extra-personal space. Studies of patients with spatial neglect Communicated by Francesca Frassinetti. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00221-020-05971-z) contains supplementary material, which is available to authorized users. * Daisuke Mine [email protected]‑tokyo.ac.jp 1
support the distinction between spatial representations in these two spaces. A line bisection task, in which patient’s bisect lines presented to them are typically used to assess spatial neglect. Spatial neglect patients always show a strong rightward (or leftward) bias from the midpoint of the line, as if the left half (or the right half) of the line is entirely missing. However, this unilateral neglect is observed only when the lines are presented in the patients’ PPS, but not in extra-personal space (Halligan and Marshall 1991). T
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