Abstract
Previous work has reported that it is not difficult to give people the illusion of ownership over an artificial body, providing a powerful tool for the investigation of the neural and cognitive mechanisms underlying body perception and self consciousness. We present an experimental study that uses immersive virtual reality (IVR) focused on identifying the perceptual building blocks of this illusion. We systematically manipulated visuotactile and visual sensorimotor contingencies, visual perspective, and the appearance of the virtual body in order to assess their relative role and mutual interaction. Consistent results from subjective reports and physiological measures showed that a first person perspective over a fake humanoid body is essential for eliciting a body ownership illusion. We found that the illusion of ownership can be generated when the virtual body has a realistic skin tone and spatially substitutes the real body seen from a first person perspective. In this case there is no need for an additional contribution of congruent visuotactile or sensorimotor cues. Additionally, we found that the processing of incongruent perceptual cues can be modulated by the level of the illusion: when the illusion is strong, incongruent cues are not experienced as incorrect. Participants exposed to asynchronous visuotactile stimulation can experience the ownership illusion and perceive touch as originating from an object seen to contact the virtual body. Analogously, when the level of realism of the virtual body is not high enough and/or when there is no spatial overlap between the two bodies, then the contribution of congruent multisensory and/or sensorimotor cues is required for evoking the illusion. On the basis of these results and inspired by findings from neurophysiological recordings in the monkey, we propose a model that accounts for many of the results reported in the literature.
Highlights
The experience of our body results from the complex interplay of various perceptual streams involving vision, touch, proprioception, interoception, motor control, and vestibular sensations
We found that the illusion of ownership can be generated when the virtual body has a realistic skin tone and spatially substitutes the real body seen from a first person perspective
Participants were asked to focus their attention on the virtual body, and after about 30 s they were exposed to a disturbing event: the lower legs slowly moved away from the rest of the body for 10 s, covering a distance of about 1 m in the virtual room, and after that they returned to the original position to recompose the whole body. The choice of this particular kind of disturbing event instead of a more classic threat to the virtual body is based on two main motivations: first, we wanted to avoid any kind of threat directed to the spatial location of the real body; second, we looked for an event that explicitly breaks the integrity of the whole body
Summary
The experience of our body results from the complex interplay of various perceptual streams involving vision, touch, proprioception, interoception, motor control, and vestibular sensations Strong evidence supporting this statement comes from a number of neurological conditions where the sense of the body becomes altered as a consequence of focal brain lesions, limb amputation or deafferentation. Altered body perceptions analogous to those experienced in lesioned patients, can be temporally induced in healthy subjects in controlled experimental settings, where the delivery of anomalous sensory stimuli is systematically manipulated. These altered perceptual states are usually referred to as bodily illusions and have been extensively used for studying body perception, self-consciousness and their underlying neural correlates. Experimentally controlled bodily illusions allow, to some extent, the isolation of the various components that converge in the holistic experience of our bodies
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