Vestibular modulation of peripersonal space boundaries.

Human-environment interactions are mediated through the body and occur within the peripersonal space (PPS), the space immediately adjacent to and surrounding the body. The PPS is taken to be a critical interface between the body and the environment, and indeed, body-part specific PPS remapping has been shown to depend on body-part utilization, such as upper limb movements in otherwise static observers. How vestibular signals induced by whole-body movement contribute to PPS representation is less well understood. In a series of experiments, we mapped the spatial extension of the PPS around the head while participants were submitted to passive whole-body rotations inducing vestibular stimulation. Forty-six participants, in three experiments, executed a tactile detection reaction time task while task-irrelevant auditory stimuli approached them. The maximal distance at which the auditory stimulus facilitated tactile reaction time was taken as a proxy for the boundary of peri-head space. The present results indicate two distinct vestibular effects. First, vestibular stimulation speeded tactile detection indicating a vestibular facilitation of somatosensory processing. Second, vestibular stimulation modulated audio-tactile interaction of peri-head space in a rotation direction-specific manner. Congruent but not incongruent audio-vestibular motion stimuli expanded the PPS boundary further away from the body as compared to no rotation. These results show that vestibular inputs dynamically update the multisensory delineation of PPS and far space, which may serve to maintain accurate tracking of objects close to the body and to update spatial self-representations.