Environmental motion presented ahead of self-motion modulates the heading direction estimation

Department of Biomedical Engineering (Human Factors Engineering)Safely navigating through an environment requires an accurate estimation of self-motion. This accuracy can be relatively easily achieved when the observer is moving in a stationary environment because perceived retinal motion is only generated from self-motion. However, when the observer moves in a moving environment, this individually moving environment may be wrongly attributed to be caused by self-motion. Studies have shown that when object motion was presented during self-motion. The heading deviated from the true heading direction. This is explained by the visual-vestibular integration in heading estimation. However, the existing literature has predominantly focused on visual and vestibular processing during self-motion, neglecting the investigation of visual motion stimuli preceding self-motion. In real-world scenarios, we often observe visual motion before initiating our movements, which could provide valuable information for interpreting retinal motion during self-motion. The main objective of this thesis is to explore the role of visual motion observed before self-motion in interpreting visual motion generated by the environment and self-motion during self-motion. Participants were passively moved in a motion platform and they were asked to report their heading estimation by adjusting a probe presented after they moved. Self-motion was paired with visual motion that occurred before and during the self-motion. The results indicate that the duration of visual motion presented before self-motion affects heading bias, with longer presentations leading to reduced bias. This suggests that our perceptual system subtracts visual motion observed before self-motion from the perceived retinal motion during self-motion, resulting in the cancellation of the world motion component. However, even with longer durations of visual motion before self-motion, a bias was still observed, indicating that the system does not completely subtract the entire visual motion speed preceding self-motion. We propose that this residual bias may be attributed to a slow-speed bias, where visual motion is perceived as slower than its actual speed. This bias can occur due to the observer's strong prior knowledge that the world is predominantly stationary, and judgments are based on noisy measurements. To test the accountability of the slow-speed bias in our observed data, we fit a linear model that incorporates a slow-speed bias coefficient in the optimal cue integration of visual and vestibular signals for heading estimation. The results of our analysis demonstrate agreement between the observed data and the estimates from our linear model, supporting the hypothesis that visual motion observed before self-motion is subtracted during heading estimation, and this visual motion is scaled by the slow-speed bias. The thesis begins with a comprehensive literature review that explores the intricate relationship between visual function and postural balance, encompassing crucial aspects such as visual acuity, contrast sensitivity, and visual motion perception. Building upon this foundation, Chapter 2 delves deeper into the intricate link between visual motion perception and balance control. To further unravel the impact of visual motion on self-motion perception, Chapter 3 presents a study where observers were asked to report their heading direction while being passively moved on a motion platform and simultaneously exposed to visual motion stimuli. By manipulating the temporal delay between visual and self-motion, we aimed to assess the influence of visual motion on self-motion perception. Chapter 4 delves into the fascinating realm of processing visual motion stimuli preceding self-motion and its profound influence on heading estimation. By skillfully manipulating the onset of visual motion relative to self-motion, we gain control over the duration of the presentation of visual motion before self-motion. Despite our initial expectation of observing no bias with the longest duration of visual motion before self-motion, intriguingly, we still detected heading bias, suggesting the presence of sub-optimal subtraction processes. A plausible explanation for this phenomenon lies in the influence of slow-speed bias in visual motion perception, which affects the accurate estimation of motion speed. To comprehensively investigate the contribution of slow-speed bias and its impact on heading estimation, Chapter 5 introduces three distinct conditions of visual motion before self-motion while maintaining constant visual motion during self-motion across all conditions. Through strategic manipulation of the speed of visual motion before self-motion, any variations in heading estimation are likely attributable to the visual motion information observed before the observer's movement. To validate and explain these results, we employ an optimal cue integration model that incorporates the constant slow-speed bias and visual motion before self-motion. Overall, the findings presented in this thesis provide profound insights into the intricate processing of visual motion before self-motion and its far-reaching implications for accurate heading estimation in real-world scenarios. By unraveling this complex relationship, we gain a deeper understanding of the challenges inherent in estimating heading direction in dynamic environments.clos

Ageing vision and falls: a review

Background: Falls are the leading cause of accidental injury and death among older adults. One of three adults over the age of 65 years falls annually. As the size of elderly population increases, falls become a major concern for public health and there is a pressing need to understand the causes of falls thoroughly. Main body of the abstract: While it is well documented that visual functions such as visual acuity, contrast sensitivity, and stereo acuity are correlated with fall risks, little attention has been paid to the relationship between falls and the ability of the visual system to perceive motion in the environment. The omission of visual motion perception in the literature is a critical gap because it is an essential function in maintaining balance. In the present article, we first review existing studies regarding visual risk factors for falls and the effect of ageing vision on falls. We then present a group of phenomena such as vection and sensory reweighting that provide information on how visual motion signals are used to maintain balance. Conclusion: We suggest that the current list of visual risk factors for falls should be elaborated by taking into account the relationship between visual motion perception and balance control