Effects of active and passive viewpoint jitter on vection in depth
Recent studies have shown that the vection in depth experienced by stationary observers viewing constant velocity radial flow can be enhanced by adding simulated viewpoint jitter/oscillation. This studyexamined the effect of manipulating visualvestibular conflict on the perceived strength and speed ofvection in depth. Four conditions were examined: (i) radial flow without viewpoint jitter viewed by stationary observers (consistent visualvestibular inputs); (ii) radial flowwith viewpoint jitter synchronized to lateral head oscillation (consistent inputs); (iii) radial flow with viewpoint jitter viewed by stationary observers (inconsistent inputs); (iv) radial flow without viewpoint jitter viewed during head oscillation (inconsistent inputs). We found that the strength and perceived speed of vection in depth was always greaterwhensimulatedviewpoint jitterwas introduced.No further vection enhancementwas found when this jitter was generated by active head oscillationeven though passive jitter conditions should have generated significant sensory conflicts, whereas active jitter conditionswould not. Active head oscillation without display jitter also had little effect, producing similar vection strength/speed ratings to stationary observation of non-jittering optic flow. Horizontal eye tracking suggested that retinal stimulation was similar between comparable active and passive viewing conditions. This stabilization of the retinal image across active and passive conditions appeared to be due to cooperative engagement of the translational vestibuloocular reflex and the visually driven ocular following response. Rather than providing evidence for synergistic integration of self-motion perception, these findings obtained with low-frequency sensory stimuli suggest that self-motion perception is dominated by visual processing centres.