Vection Induced by Consistent and Inconsistent Multisensory Stimulation

This study examined physical and simulated self-motion along the horizontal and depth axes. Subjects viewed optic flow which consisted of: (i) a component that simulated constant velocity self-motion; and (ii) a component that simulated oscillation of their viewpoint. In active self-motion conditions, the latter flow component was either in- or out-of-phase with the observer's own (tracked) oscillatory head movements. In passive self-motion conditions, stationary subjects simply viewed playbacks of the oscillating displays generated in previous physical self-motion conditions. We found that adding active in-phase horizontal oscillation to radial flow resulted in a modest vection advantage compared to active out-of-phase horizontal oscillation and passive horizontal display oscillation conditions. By contrast, when actively generated fore-aft display oscillation was added to either radial or lamellar flow we found similar vection strength ratings for both in-phase and out-of-phase depth oscillation. We conclude that multisensory input can enhance the visual perception of self-motion in some situations, but may not have to be consistent (i.e., ecological) to generate compelling vection in depth.