Embodying their own wheelchair modifies extrapersonal space perception in people with spinal cord injury

Abstract

Despite the many links between body representation, acting and perceiving the environment, no research has to date explored whether specific tool embodiment in conditions of sensorimotor deprivation influences extrapersonal space perception. We tested 20 spinal cord injured (SCI) individuals to investigate whether specific wheelchair embodiment interacts with extrapersonal space representation. As a measure of wheelchair embodiment, we used a Body View Enhancement Task in which participants (either sitting in their own wheelchair or in one which they had never used before) were asked to respond promptly to flashing lights presented on their aboveand below-lesion body parts. Similar or slower reaction times (RT) to stimuli on the body and wheelchair indicate, respectively, the presence or absence of tool embodiment. The RTs showed that the participants embodied their own wheelchair but not the other one. Moreover, they coded their deprived lower limbs as external objects and, when not in their own wheelchair, also showed disownership of their intact upper limbs. To measure extrapersonal space perception, we used a novel, ad-hoc designed paradigm in which the participants were asked to observe a 3D scenario by means of immersive virtual reality and estimate the distance of a flag positioned on a ramp. In healthy subjects, errors in estimation increased as the distance increased, suggesting that they mentally represent the physical distance. The same occurred with the SCI participants, but only when they were in their own wheelchair. The results demonstrate for the first time that toolembodiment modifies extrapersonal space estimations.

Proprioceptive drift is affected by the intermanual distance rather than the distance from the body’s midline in the rubber hand illusion

“…The results were expressed in terms of Bayes factors (BF 10 ), where BF 10 ≤ 0.33 indicates equal data distributions (i.e., the null hypothesis is supported), BF 10 within 3 and 0.33 is considered as inconclusive (i.e., the Bayesian approach does not allow to confirm the null or the alternative hypothesis), and BF 10 ≥ 3 indicates the different data distributions (i.e., the alternative hypothesis is supported). Finally, BF 10 = 1 indicates that the null and the alternative hypothesis are equal (Lee & Wagenmakers, 2013;Scandola et al, 2019).…”

Cognitive Training Improves Disconnected Limbs’ Mental Representation and Peripersonal Space after Spinal Cord Injury

“…Furthermore, de-afferentation and de-efferentation cause indirect plasticity processes in brain networks that extend beyond the sensorimotor system (for reviews see: [15][16][17]), and probably also contribute to cognitive changes. Experimental studies have indeed demonstrated changes in SCI people's representations of body [18][19][20][21], action [22][23][24] and space [20,[25][26][27], which are topographically organised and as such reflect the topography of the disconnected body parts.…”

Go Virtual to Get Real: Virtual Reality as a Resource for Spinal Cord Treatment

“…The use of VR techniques to help patients understand neurological pathologies in addition to rehabilitation activities offers great opportunities for basic research. A recent study [65] showed how using a VR experimental paradigm can help SCI patients better understand the relationship between their own bodies at the level of the wheelchair and their perception of extra-personal space. The understanding of how our minds shape the representations of the body, the peri-personal space, and how these representations are encoded within our brains is a particularly discussed topic in basic research.…”