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Neural mechanisms of body ownership and the projection of ownership onto artificial bodies

Final Report Summary - BODY-OWNERSHIP (Neural mechanisms of body ownership and the projection of ownership onto artificial bodies.)

Our project addressed the question of how we come to perceive ownership over our bodies. This question can be framed in terms of a multisensory binding problem: how are visual, tactile and proprioceptive information combined to obtain a single coherent object that is one's own body? Our results suggest that the underlying mechanism is the integration of multisensory signals by populations of neurons in the premotor cortex and the posterior parietal cortex.

The hypothesis under investigation was that parts of the body are distinguished from the external world by the patterns they produce of correlated information from different sensory modalities (i.e. vision, touch and muscle sense). We theorized that the detection of these correlations would occur within neuronal populations that integrate multisensory information from the space near the body. To test these predictions, we used a combination of functional magnetic resonance imaging and human behavioral experiments. To experimentally manipulate the feeling of body ownership, perceptual illusions were used where healthy individuals experienced that a rubber hand was their own, that a mannequin was their body, or that they were outside their physical body and looking at it from the perspective of another individual (“out-of-body illusion”). Our behavioral results demonstrated that ownership of limbs and entire bodies depend on the temporal and spatial congruency of visual, tactile and proprioceptive signals in body-centered reference frames and that visual information from the first-person perspective plays a crucial role. Our imaging data showed that neuronal populations in the premotor and intraparietal cortices are active when humans sense they own limbs or entire bodies, which supports the hypothesis that the integration of multisensory information in body-centered coordinates is crucial for body ownership. Moreover, our fMRI data revealed that the perceptual experience of owning a full body, as opposed to fragmented parts, additionally requires the engagement of active neuronal populations in the premotor and posterior parietal cortices, which integrate visual, tactile and proprioceptive information across body segments.

By clarifying how the normal brain produces a sense of ownership of one’s body, we can learn how to project ownership onto artificial bodies and simulated virtual bodies. This capability could have groundbreaking beyond-state-of-the-art applications in the fields of virtual reality, neuroprosthetics, and neurorobotics. In the present project, we made several important advances towards these goals. For the first time, we described how upper-limb amputees could be made to experience a cosmetic prosthetic hand or an advanced humanoid robotic prosthesis as part of their own body, simply by tricking the mind with an illusion. This finding represents an important contribution to the field of neuroprosthetics where a major goal is to develop artificial limbs that feel like real parts of the body. Moreover, our experiments that clarify how people can be induced to experience an illusion of owning an entire artificial body provide proof-of-concept that the feeling of ownership can be projected onto humanoid robots for teleoperator applications.