Audiogravic and oculogravic illusions represent a unified spatial remapping

Individuals exposed to both an increase in magnitude and a rotation of the gravitoinerital acceleration vector experience changes in visual and auditory localization and apparent body orientation. These effects are known as the oculogravic, audiogravic and somatogravic illusions, respectively. In our main experiment, we measured the magnitude, direction, and time course of the audiogravic and oculogravic illusions in recumbent subjects (n = 6) exposed to an increase to 2 g and a simultaneous 60 degrees rotation of the gravitoinertial acceleration (GIA) vector in their azimuthal plane (around their z-axis) in the Brandeis slow rotation room. In separate runs, subjects used a pointer to indicate the apparent azimuthal location of auditory and visual targets and of their head midline. Parallel, time linked changes in auditory, visual, and haptic localization of comparable magnitude and direction occurred. Two additional subjects adjusted the onset asynchrony of a pair of pulsing tactors on the forehead until they experienced a fused, midline sensation. A vibrotactile shift occurred during exposure to altered GIA in the same direction as the auditory, visual, and haptic shifts. These parallel multimodal results point to a GIA-induced remapping of a peripersonal spatial referent as underlying the changes in localization of auditory, visual, and somatosensory stimuli. Vestibular, somatosensory, and oculomotor signals could contribute to the proposed shift in the reference system.