The rubber hand illusion in microgravity and water immersion

Abstract

Our body has evolved in terrestrial gravity and altered gravitational conditions may affect the sense of body ownership (SBO). By means of the rubber hand illusion (RHI), we investigated the SBO during water immersion and parabolic flights, where unconventional gravity is experienced. Our results show that unconventional gravity conditions remodulate the relative weights of visual, proprioceptive, and vestibular inputs favoring vision, thus inducing an increased RHI susceptibility.

Fig. 1. Experimental settings.

Upper panel (a): Parabolic flight experiment. Participants underwent the RHI procedure during a parabolic flight: in normal gravity (1 g, in red) during steady horizontal flight, and in microgravity (0 g, in blue). The tactile stimulation was delivered via a fully automated system assembled ad hoc for the experiment. Lower panel (b, c): Swimming pool experiment. Participants underwent the RHI both in an ordinary laboratory (on ground condition, in orange, b) and in a private swimming pool (water immersion condition, in green, c). For graphical purposes, the coat used to cover the right shoulder and arm of participants in both experiments is not shown in the figure.

Fig. 2. Results.

Upper panel (a–f): Parabolic flight experiment. Lower panel (g–l): Swimming pool experiment. Error bars represent standard errors of the means. Dots represent single-subject values, i.e., the mean of each participant’s judgment in each condition. °tendency toward statistical significance; *p < 0.05; ***p < 0.001. Values are normalized in z scores.