Sense of ownership and not the sense of agency is spatially bounded within the space reachable with the unaugmented hand

Abstract

While reaching for a coffee cup, we are aware that the hand we see belongs to us and it moves at our will (reflecting our senses of ownership and agency, respectively), and that the cup is within our hand’s reach rather than beyond it (i.e., in reachable space, RS, rather than in non-reachable space, NRS). Accepted psychological explanations of our sense of ownership, sense of agency, and our perception of space surrounding the body as RS or NRS propose a unitary dependence on Euclidean distance from the body. Here, we propose an alternate, affordance-based explanation of experienced ownership, agency, and perception of space surrounding the body as RS and NRS. Adult participants experienced the static rubber hand illusion (RHI) and its dynamic variant, while the rubber hand was either within their arm’s reach (i.e., in self-identified RS) or beyond it (i.e., in self-identified NRS). We found that when the participants experienced synchronous visual and tactile signals in the static RHI, and synchronous visual and kinesthetic signals in the dynamic RHI, they felt illusory ownership when the rubber hand was in RS but not when it was in NRS. Conversely, when the participants experienced synchronous visual and kinesthetic signals in the dynamic RHI, they felt agency, regardless of the rubber hand’s location. In addition, illusory ownership was accompanied by proprioceptive drift, a feeling that their hand was closer to the rubber hand than it actually was, but agency was not accompanied by proprioceptive drift. Together, these results indicate that our sense of ownership, while malleable enough to incorporate visible non-corporeal objects resembling a body part, is spatially constrained by proprioceptive signals specifying that body part’s actual location. In contrast, our sense of agency can incorporate a visible non-corporeal object, independent of its location with respect to the body. We propose that the psychological processes mediating our sense of ownership are closely linked with our perception of space surrounding the body, and that the spatial independence of our sense of agency reflects the coupling between our actions and perception of the environment, such as while using handheld tools as extensions of our body.