Sensory conRict !.heories predict thai adding simulatcd viewpoint oscillUlion to sclf-motion displays should generate significant and sustained visual-vestibul ar conniet and reduce !.he likelihood of itlusory self· motion (vccl ion). However. research sh.ows th.at viewpoinl oscillation enhances vectioil in uprigh.t observers. This study examined whclh.cr the oscil lation advantage for veclion depends on head orientalion with respect to gravily. Displays that simulated forwardlbackward self-motion wi th/Without horizontal and vertical viewpoint oscillation were presented to observers in uprigh.t (sealed and standing) and lying (supine. prone. and len side down) body postures. Viewpoint oscillation was found to enhance vection for 0111 oflhe body postures tested. Vection also tended to be Slronger in upright postures th.an in lying postures. Changing the orientation or lhe head wi th reSpeCt 10 gravity was expected to alter the degree/saliency of the sensory confl ict, which may explain the overall postul"c-based differences in vcction strength. However, th is docs not explain why the oscillation advantage for veclion persisted for all postures. Thus, the current postural and osci ll ation based vection findings appear to be better explained by ecology: Upright postures and oscillating flow (that arc thc nann during self-motion) improved vection. whereas lying postures and smooth optic flows (which are less common) impaired veelion.