The Effect of Perceived Self-Orientation on the Perception of Visually Induced Self-Motion

In certain environments the direction of up indicated by vision and gravity can be in conflict where these directions do not agree. Some people resolve this conflict by relying on their visual cues. In this case, when a participant and the room in which they are sitting are both tilted together, they would feel as if they were standing upright and would experience what is called a Visual Reorientation Illusion (VRI). A VRI on Earth might result from either (1) ignoring the gravity up in favour of the visual up, resulting in a higher visual weighting, or (2) misinterpreting the ambiguous vestibular acceleration cue not as a tilt but as a translation. In Chapter 2, I present evidence that during a VRI individuals require less visual motion to perceive that they have traveled through a specified distance: the move-to-target task. This might result from an enhancement of the visual cue due to a higher visual weighting while down-weighting the conflicting gravity cue, here referred to as my reweighting hypothesis. In Chapter 3, I find that people with VRIs actually have a lower visual weight and higher gravity weight when determining their perceived upright. This suggests that either the reweighting theory is incorrect or that the participants with a higher gravity weight might be more likely to detect, and then reweight, the conflicting visual and vestibular cues. In Chapter 4, I find that when the gravity cue is removed by moving into a 0g environment, initially there is no difference in performance on the move-to-target task compared to on Earth, but after adapting to microgravity and also upon return to 1g, participants need more visual motion to feel they have passed through a specified distance. Chapter 4 provides further evidence that my reweighting theory is incorrect. My research demonstrates that even within the same environment and while viewing the same stimuli, different people can have different interpretations of the environment which are related to changes in behaviour. Specifically, a persons perceived orientation can affect their self-motion perception. The findings are discussed in terms of sensory cue conflict and reweighting, as well as differences between how we perceive visual motion versus how we use it.