Visual gravity contributes to subjective first-person perspective

A fundamental component of conscious experience involves a first-person perspective (1PP), characterized by the experience of being a subject and of being directed at the world. Extending earlier work on multisensory perceptual mechanisms of 1PP, we here asked whether the experienced direction of the 1PP (i.e. the spatial direction of subjective experience of the world) depends on visual-tactile-vestibular conflicts, including the direction of gravity. Sixteen healthy subjects in supine position received visuo-tactile synchronous or asynchronous stroking to induce a full-body illusion. In the critical manipulation, we presented gravitational visual object motion directed toward or away from the participant's body and thus congruent or incongruent with respect to the direction of vestibular and somatosensory gravitational cues. The results showed that multisensory gravitational conflict induced within-subject changes of the experienced direction of the 1PP that depended on the direction of visual gravitational cues. Participants experienced more often a downward direction of their 1PP (incongruent with respect to the participant's physical body posture) when visual object motion was directed away rather than towards the participant's body. These downward-directed 1PP experiences positively correlated with measures of elevated self-location. Together, these results show that visual gravitational cues contribute to the experienced direction of the 1PP, defining the subjective location and perspective from where humans experience to perceive the world.