Thesis (M.S.)--University of Florida, 2002. / Title from title page of source document. Includes vita. Includes bibliographical references.

Thesis (Ph. D.)--Carnegie Mellon University, 2003. / "September 2003." Includes bibliographical references.

Thesis (M. Phil.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 90-99). Also available in print.

Thesis (M. Phil.)--University of Hong Kong, 1985.

It is now possible for physical objects to have a dynamic digital presence via active identification codes that can be scanned via ubiquitous devices such as smart phones or tablets. En-co.de is a web service for the generation, storing, retrieval, and augmentation of metadata associated with physical objects. The service is built upon the concept that metadata associated with an object can be retrieved through a Quick Response (QR) coded URL. En-co.de serves to link a physical entity to a digital archive of information and provides services such as geolocation and SMS text alerts when an object's identifier, or tag, is scanned. I provide an analysis of QR code qualitative characteristics, the architecture for the en-co.de web service, a scalability study of the en-co.de architecture, and the results of the completed service in production in this report. In addition, the analysis is complemented with an evaluation of comparable identification schemes and web services. / text

published_or_final_version / Public Health / Master / Master of Public Health

Perceiving the path we are travelling on is important for successful navigation. Relative motion between the world and the observer generates optical flow on the retinae (retinal flow). Gibson (1950) pointed out that when travelling on a straight path with no eye, head, or body rotation, retinal flow is radial and the stationary point indicates the instantaneous direction of travelling, or heading, of the observer. The straight path can then be recovered as it coincides with heading. Nevertheless, it is rarely the case that people travel with no rotation. Instead, they normally look at different points of interest when they are navigating. The result of changing one's gaze or rotating one's head is the addition of a rotational component, which is a laminar flow, to the flow field. The rotational component shifts the stationary point from heading and makes heading perception difficult. Extensive research has been conducted on how the human visual system removes the rotational component of the retinal flow and how extra-retinal information, such as efferent copies of eye muscle commands, may contribute to this process. The paths on which people travel are not always straight, but often curved. When a path is curved, it no longer coincides with heading. In this case, heading is the tangent of the path. Researchers have proposed theories to explain how curved paths are perceived. Each of them requires different visual information and gaze conditions (e.g., fixating on a target or gazing along the heading direction). They can be categorized by whether or not path perception depends on heading perception. The goal of this thesis is to systematically examine different theories of path perception and determine how humans perceive curved paths. Study 1 examined different path perception theories by comparing human path perception performance in various gaze conditions and with the availability of various optic flow information. Study 2 investigated whether path perception depends on heading perception. Study 3 examined the contribution of reference objects to path perception. Study 4 investigated how extra-retinal informationcontribute to path perception. The experiments that I present here show that (a) when there is no extra-retinal information, path perception is accurate only when one's gaze is along heading such that the rotation in the flow field is equal to path rotation; (b) when one's gaze is not along heading such that the rotation in the flow field is not equal to path rotation, path perception is inaccurate. Adding more visual information, such as acceleration, dense flow field, and/ or reference objects does not improve the accuracy; (c) eye movement signals support accurate path perception only in the natural case of self-motion in which body orientation is aligned with heading such that eye movement signals help to stabilize heading in the body-centric coordinate system. / published_or_final_version / Psychology / Doctoral / Doctor of Philosophy

Human observers can perceive self-motion from optic flow for both circular paths and straight paths. However, when view does not rotate during travel on a circular path, observers often show significant bias in path judgments from optic flow. A proposed explanation is that human observers use the velocity field of optic flow for perception of self-motion and assume that path curvature is accompanied by body rotation. Use of a scene-based strategy, as opposed to optic flow, could potentially reduce the bias in judgments of circular path with no view rotation. It has been shown that human observers can judge heading direction from a sequence of static pictures of a scene, suggesting that observers can perceive self-motion from change in observer position relative to a scene. Another previous study found that showing the same configuration of landmarks repeatedly improved performance in a steering task, suggesting that familiarity of a scene may further improve perception of self-motion and steering control. In this thesis, I explored the effect of scene information on judgments of circular path and steering control. Experiments 1 and 2 tested path judgments for simulated travel along a circular path. Observers viewed 1 s presentations of optic flow and adjusted a response pole to lie on their future path, i.e. where they would intercept the pole if they keep travelling on the current path. Precision and accuracy of judgments were compared across conditions that varied in the presence and consistency of landmarks. I found no effect of landmarks on precision and accuracy, and curvature underestimation remained present in all conditions. Experiment 3 tested whether familiarity with a scene can improve steering control. I used the same steering task by Andersen and Enriquez (2006). During a trial, heading direction was perturbed horizontally in a smooth, pseudo-random manner, as if unexpectedly wind perturbed a car and caused it to slide to the left and right while driving straight ahead. Observers were instructed to counteract these perturbations and steer to maintain a straight path of travel. Contrary to previous findings, I found no effect of scene familiarity on steering control. I found no benefit from landmarks in any of the conditions tested in this thesis. These results suggest that scene information has a limited role for path judgments and steering control. / published_or_final_version / Psychology / Master / Master of Philosophy

When we stand still and do not move our eyes and head, the motion of an object in the world or the absence thereof is directly given by the motion or quiescence of the retinal image. Self-motion through the world however complicates this retinal image. During self-motion, the whole retinal image undergoes coherent global motion, called optic flow. Self-motion therefore causes the retinal motion of objects moving in the world to be confounded by a motion component due to self-motion. How then do we perceive the motion of an object in the world when we ourselves are also moving? Although non-visual information about self-motion, such as provided by efference copies of motor commands and vestibular stimulation, might play a role in this ability, it has recently been shown that the brain possesses a purely visual mechanism that underlies scene-relative object motion perception during self-motion. In the flow parsing hypothesis developed by Rushton and Warren (2005; Warren & Rushton, 2007; 2009b), the brain uses its sensitivity to optic flow to detect and globally remove retinal motion due to self-motion and recover the scene-relative motion of objects. Research into this perceptual ability has so far been of a qualitative nature. In this thesis, I therefore develop a retinal motion nulling paradigm to measure the gain with which the flow parsing mechanism uses the optic flow to remove the self-motion component from an object’s retinal motion. I use this paradigm to investigate how accurate scene-relative object motion perception during self-motion can be based on only visual information, whether this flow parsing process depends on a percept of the direction of self-motion and the tuning of flow parsing, i.e., how it is modulated by changes in various stimulus aspects. The results reveal that although adding monocular or binocular depth information to the display to precisely specify the moving object’s 3D position in the scene improved the accuracy of flow parsing, the flow parsing gain was never up to the extent required by the scene geometry. Furthermore, the flow parsing gain was lower at higher eccentricities from the focus of expansion in the flow field and was strongly modulated by changes in the motion angle between the self-motion and object motion components in the retinal motion of the moving object, the speeds of these components and the density of the flow field. Lastly, flow parsing was not affected by illusory changes in the perceived direction of self-motion. In conclusion, visual information alone is not sufficient for accurate perception of scene-relative object motion during self-motion. Furthermore, flow parsing takes the 3D position of the moving object in the scene into account and is not a uniform global subtraction process. 8e observed tuning characteristics are different from those of local perceived motion interactions, providing evidence that flow parsing is a separate process from these local motion interactions. Finally, flow parsing does not depend on a prior percept of self-motion direction and instead directly uses the input retinal motion to construct percepts of scene-relative object motion during self-motion. / published_or_final_version / Psychology / Doctoral / Doctor of Philosophy

Human use both optic flow and target egocentric direction cues to guide selfmotion at walking speed. The first study examined whether people change their reliance on the two cues when they are controlling high-speed steering, e.g. driving a car? In Experiment 1, I simulated two viewing conditions. In the opticflow only condition, the participant's virtual gaze direction was fixed on the target which was placed 10° away from their straight ahead. The target egocentric direction was fixed during steering and was thus unavailable for steering control. Participants steered to align their heading but not their path of forward travel with the target at all travel speeds tested. In the optic flow-plus-egocentric direction condition, the participant's virtual gaze direction was aligned with heading which was displaced 10° away from their straight ahead. The target egocentric direction changed during steering and was thus available for steering control. Participants’ steering was affected by the heading displacement at all travel speeds tested. The faster and larger reduction of heading error observed at higher travel speed for both viewing conditions was mirrored by an increase in the precision of heading judgment in the corresponding heading perception experiment (Experiment 2). The findings support that while people are increasingly more accurate and efficient in using heading specified by optic flow for steering when travel speed increases, high-speed travel does not affect the type of visual strategy used for the control of steering toward a goal. The second study examined how different attentional loads affected people’s steering toward a goal at both low and high travel speeds. In Experiment 3, I used the same display setting as the optic flow-plus-egocentric direction condition in Experiment 1 for the steering task. Participants were asked to steer toward a red post target with (1) no attention tracking task, (2) concurrently tracking one dot (low attentional load), or (3) three dots (high attentional load) among eight dots that randomly moved inside the red circle on top of the target post. I found that attentional load affected the early stage of steering control but did not affect the overall visual strategy. Experiment 4 replicated Experiment 3 except that participants were specifically instructed to center the target straight ahead or align the target with heading for the steering task. I found that attentional load only affected the early stage of steering for the centering-the-target instruction group, but affected the steering performance throughout the trial for the aligning the-target-with-heading instruction group. In both Experiments 3 and 4, while the tracking accuracy was high (> 90%) and not affected by the travel speed when the attentional load was low, it decreased more at higher travel speed when the attentional load was high. The findings suggest that people have more difficulty in dealing with high attention demanding task at high than low travel speed. Increasing attentional load affects the accuracy in using heading specified by optic flow but does not change the natural visual strategy for goal-directed selfmotion control. / published_or_final_version / Psychology / Master / Master of Philosophy