UBC Theses and Dissertations
Motion processing across spatial and temporal scales for human perception and eye movements Wu, Xiuyun
We live in a dynamic visual environment, which requires perceiving moving objects around us and acting accordingly. However, we do not yet fully understand how visual information informs perception and motor actions. This dissertation examines the perception-action link by testing how motion and expectation signals are processed for perception and for eye movements as an example of human motor action. I focus on two types of human eye movements triggered by distinct brain mechanisms: ocular torsion, the eyes’ rotation about the line of sight triggered by rotational motion, and smooth pursuit, the eyes’ continuous tracking of translational motion. Torsion is mostly controlled by subcortical brain areas, but might share early-stage cortical processing of sensory signals with perception. In contrast, smooth pursuit is controlled by subcortical and cortical areas and might therefore be more closely linked to perception, sharing both motion and expectation signal processing with perception. To test the torsion-perception link, I utilized a perceptual illusion induced by visual rotational motion. Results show that torsional velocity correlates with the perceptual illusion, potentially suggesting shared motion processing (Chapter 2.1). However, anticipatory torsion can only be elicited by trial repetition, but not by cognitive cues that induce expectation (Chapter 2.2). These results show that similar visual motion signals might drive reflexive torsion and perception. Expectation signals appear to be less effective in driving torsion. Probing the pursuit-perception link, I found dissociations between how each system processes motion and expectation signals. When integrating diverse motion signals across space, pursuit was biased to the average motion direction, whereas perception showed no consistent bias (Chapter 3). When investigating the role of expectation, I found that anticipatory pursuit followed the expected direction, whereas perception was biased in the opposite direction (Chapter 4). Overall, this dissertation reveals that perception and eye movements likely share early-stage motion processing, even for reflexive eye movements such as torsion. But perception and eye movements differ in how they utilize higher-level motion or expectation signals. The dissociations might indicate how each system optimally meets different functional demands: Perception relies on object segregation, whereas eye movements rely on signal integration.
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