Abstract
It has been suggested that the integration of multiple body-related sources of information within the peri-personal space (PPS) scaffolds body ownership. However, a normative computational framework detailing the functional role of PPS is still missing. Here we cast PPS as a visuo-proprioceptive Bayesian inference problem whereby objects we see in our environment are more likely to engender sensations as they come near to the body. We propose that PPS is the reflection of such an increased a priori probability of visuo-proprioceptive coupling that surrounds the body. To test this prediction, we immersed participants in a highly realistic virtual reality (VR) simulation of their right arm and surrounding environment. We asked participants to perform target-directed reaches toward visual, proprioceptive, and visuo-proprioceptive targets while visually displaying their reaching arm (body visible condition) or not (body invisible condition). Reach end-points are analyzed in light of the coupling prior framework, where the extension of PPS is taken to be represented by the spatial dispersion of the coupling prior between visual and proprioceptive estimates of arm location. Results demonstrate that if the body is not visible, the spatial dispersion of the visuo-proprioceptive coupling relaxes, whereas the strength of coupling remains stable. By demonstrating a distance-dependent alteration in visual and proprioceptive localization attractive pull toward one another (stronger pull at small spatial discrepancies) when the body is rendered invisible – an effect that is well accounted for by the visuo-proprioceptive coupling prior – the results suggest that the visible body grounds visuo-proprioceptive coupling preferentially in the near vs. far space.
Highlights
A large proportion of human interactions with the environment are mediated by the body and as such occur within the peripersonal space (PPS), the volume of space that surrounds and is immediately adjacent to the body[1]
More direct examinations of the relationship between the visually represented body and the multisensory peri-personal space (PPS) are largely lacking due to i) the fact that PPS has traditionally been studied in the real world and via reaction time paradigms that necessitate the presence of the body, and ii) the difficulty – or impossibility, without novel virtual reality (VR) technology - to study PPS while not displaying a body yet concurrently leaving the rest of the visual scene unchanged
All participants gave informed written consent before taking part in the experiment, which was conducted according to the protocol approved by Western Institutional Review Board (WIRB)
Summary
A large proportion of human interactions with the environment are mediated by the body and as such occur within the peripersonal space (PPS), the volume of space that surrounds and is immediately adjacent to the body[1]. In rare exceptions and making use of VR setups, D’Angelo and colleagues[41] have recently observed that body invisibility induces a contraction of interpersonal space, yet not of the judgement of their reaching limit, while Guterstam and colleagues have suggested that whole-body[42] or body-part[43] ownership over an empty space is possible Given these results, in a first aim here we sought to further probe the putative relation between bodily self-consciousness and PPS by examining whether the latter representation was “preserved yet modified” when the body was rendered invisible. This specific hypothesis is supported by the above-mentioned findings that embodiment, putatively reliant on PPS encoding[20,33,34,35], over empty spaces is possible[42,43], yet interpersonal space – a concept closely related but not identical to PPS (see see Clery & Ben Hamed[44] and Hunley & Lourenco45) – is contracted[41] when the body is rendered invisible
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