Vection in depth during consistent and inconsistent multisensory stimulation.

We examined vection induced during physical or simulated head oscillation along either the horizontal or depth axis. In the first two experiments, during active conditions, subjects viewed radial-flow displays which simulated viewpoint oscillation that was either in-phase or out-of-phase with their own tracked head movements. In passive conditions, stationary subjects viewed playbacks of displays generated in earlier active conditions. A third control, experiment was also conducted where physical and simulated fore-aft oscillation was added to a lamellar flow display. Consistent with ecology, when active in-phase horizontal oscillation was added to a radial-flow display it modestly improved vection compared to active out-of-phase and passive conditions. However, when active fore-aft head movements were added to either a radial-flow or a lamellar-flow display, both in-phase and out-of-phase conditions produced very similar vection. Our research shows that consistent multisensory input can enhance the visual perception of self-motion in some situations. However, it is clear that multisensory stimulation does not have to be consistent (i.e., ecological) to generate compelling vection in depth.