Allison, Robert2016-11-252016-11-252016-06-022016-11-25http://hdl.handle.net/10315/32680Gravity is the most pervasive force that we encounter. For instance, we observe a variety of objects being accelerated toward the Earth by gravity, but we also experience these forces when we are simply stationaryas gravity is a constant accelerationor when we are ourselves in motion, such as when we are locomoting on foot, driving a vehicle, jumping or skiing. It follows that our ability to successfully navigate our environment must somehow take into account the effects of gravity on our body's motion-detecting sensesa dynamic relationship which changes with self-motion and self-orientation. The goal of this dissertation was to investigate how body orientation relative to gravity influences visual-vestibular interactions in visually-induced perception of self-motion (i.e., vection). Specifically, I examined this relationship by placing observers in varied postures and presenting visual displays simulating forward/backward self-motion with vertical/horizontal viewpoint oscillation, that mimics components produced by head-movements in real self-motion. I found that tilting observers reduced vection and the two viewpoint oscillations similarly enhanced vection, suggesting that current postural and oscillation-based vection findings are best explained by ecology. I also examined the influence of scene structure and alignment of the body and visual motion relative to gravity on vection. Observers in different postures viewed simulated translational self-motion displays consisting of either a single rigid structure or dots. The experimental data showed that vection depended on both posture and the perceived interpretation of the visual scene, indicating that self-motion perception is modulated by high-order cognitive processes. I also found that observers reported illusory tilt of the stimulus when they were not upright. I investigated these observer reports of a posture-dependent perceived stimulus tilt by presenting upright and tilted observers with static and motion stimuli that were tilted from the graviational vertical. Postural-dependent tilt effects were found for both these stimuli and were greater for motion experienced as self-motion than external motion. Taken together, the results of this dissertation demonstrate that our perception of self-motion is influenced by gravity, and by prior experiences and internal mental representations of our visual world.enAuthor owns copyright, except where explicitly noted. Please contact the author directly with licensing requests.Physiological psychologyElectronic Thesis or Dissertation2016-11-25Self-motion perceptionVectionMultisensoryGravityBody orientation