One way to characterize the special relation that one has to one's own body is to say that only one's body appears to one from the inside. Although widely accepted, the nature of this specific experiential mode of presentation of the body is rarely spelled out. Most definitions amount to little more than lists of the various body senses (including senses of posture, movement, heat, pressure, and balance). It is true that body senses provide a kind of informational access to (...) one's own body, which one has to no other bodies, by contrast to external senses like vision, which can take many bodies as their object. But a theory of bodily awareness needs to take into account recent empirical evidence that indicates that bodily awareness is infected by a plague of multisensory effects, regardless of any dichotomy between body senses and external senses. Here I will argue in favour of a multimodal conception of bodily awareness. I will show that the body senses fail to fully account for the content of bodily experiences. I will then propose that vision helps compensate for the insufficiencies of the body senses in people who can see. I will finally argue that the multimodality of bodily experiences does not prevent privileged access to one's body. (shrink)

To offer engaging neurorehabilitation training to neurologic patients, motor tasks are often visualized in virtual reality. Recently introduced head-mounted displays allow to realistically mimic the body of the user from a first-person perspective in a highly immersive VR environment. In this immersive environment, users may embody avatars with different body characteristics. Importantly, body characteristics impact how people perform actions. Therefore, alternating body perceptions using immersive VR may be a powerful tool to promote motor activity in neurologic patients. However, the ability (...) of the brain to adapt motor commands based on a perceived modified reality has not yet been fully explored. To fill this gap, we “tricked the brain” using immersive VR and investigated if multisensory feedback modulating the physical properties of an embodied avatar influences motor brain networks and control. Ten healthy participants were immersed in a virtual environment using an HMD, where they saw an avatar from first-person perspective. We slowly transformed the surface of the avatar from human to stone. We enforced this visual change by repetitively touching the real arm of the participant and the arm of the avatar with a hammer, while progressively replacing the sound of the hammer against skin with stone hitting sound via loudspeaker. We applied single-pulse transcranial magnetic simulation to evaluate changes in motor cortical excitability associated with the illusion. Further, to investigate if the “stone illusion” affected motor control, participants performed a reaching task with the human and stone avatar. Questionnaires assessed the subjectively reported strength of embodiment and illusion. Our results show that participants experienced the “stone arm illusion.” Particularly, they rated their arm as heavier, colder, stiffer, and more insensitive when immersed with the stone than human avatar, without the illusion affecting their experienced feeling of body ownership. Further, the reported illusion strength was associated with enhanced motor cortical excitability and faster movement initiations, indicating that participants may have physically mirrored and compensated for the embodied body characteristics of the stone avatar. Together, immersive VR has the potential to influence motor brain networks by subtly modifying the perception of reality, opening new perspectives for the motor recovery of patients. (shrink)