Depth from Refraction Using a Transparent Medium with Unknown Pose and Refractive Index

published_or_final_versio

Deformable Beamsplitters: Enhancing Perception with Wide Field of View, Varifocal Augmented Reality Displays

An augmented reality head-mounted display with full environmental awareness could present data in new ways and provide a new type of experience, allowing seamless transitions between real life and virtual content. However, creating a light-weight, optical see-through display providing both focus support and wide field of view remains a challenge. This dissertation describes a new dynamic optical element, the deformable beamsplitter, and its applications for wide field of view, varifocal, augmented reality displays. Deformable beamsplitters combine a traditional deformable membrane mirror and a beamsplitter into a single element, allowing reflected light to be manipulated by the deforming membrane mirror, while transmitted light remains unchanged. This research enables both single element optical design and correct focus while maintaining a wide field of view, as demonstrated by the description and analysis of two prototype hardware display systems which incorporate deformable beamsplitters. As a user changes the depth of their gaze when looking through these displays, the focus of virtual content can quickly be altered to match the real world by simply modulating air pressure in a chamber behind the deformable beamsplitter; thus ameliorating vergence–accommodation conflict. Two user studies verify the display prototypes’ capabilities and show the potential of the display in enhancing human performance at quickly perceiving visual stimuli. This work shows that near-eye displays built with deformable beamsplitters allow for simple optical designs that enable wide field of view and comfortable viewing experiences with the potential to enhance user perception.Doctor of Philosoph

Descending premotor target tracking systems in flying insects

The control of behaviour in all animals requires efficient transformation of sensory signals into the task-specific activation of muscles. Predation offers an advantageous model behaviour to study the computational organisation underlying sensorimotor control. Predators are optimised through diverse evolutionary arms races to outperform their prey in terms of sensorimotor coordination, leading to highly specialised anatomical adaptations and hunting behaviours, which are often innate and highly stereotyped. Predatory flying insects present an extreme example, performing complex visually-guided pursuits of small, often fast flying prey over extremely small timescales. Furthermore, this behaviour is controlled by a tiny nervous system, leading to pressure on neuronal organisation to be optimised for coding efficiency. In dragonflies, a population of eight pairs of bilaterally symmetric Target Selective Descending Neurons (TSDNs) relay visual information about small moving objects from the brain to the thoracic motor centres. These neurons encode the movement of small moving objects across the dorsal fovea region of the eye which is fixated on prey during predatory pursuit, and are thought to constitute the commands necessary for actuating an interception flight path. TSDNs are characterised by their receptive fields, with responses of each TSDN type spatially confined to a specific portion of the dorsal fovea visual field and tuned to a specific direction of object motion. To date, little is known about the descending representations mediating target tracking in other insects. This dissertation presents a comparative report of descending neurons in a variety of flying insects. The results are organised into three chapters: Chapter 3 identifies TSDNs in demoiselle damselflies and compares their response properties to those previously described in dragonflies. Demoiselle TSDNs are also found to integrate binocular information, which is further elaborated with prism and eyepatch experiments. Chapter 4 describes TSDNs in two dipteran species, the robberfly Holcocephala fusca and the killerfly Coenosia attenuata. Chapter 5 describes an interaction between small- and wide-field visual features in TSDNs of both predatory and nonpredatory dipterans, finding functional similarity of these neurons for prey capture and conspecific pursuit. Dipteran TSDN responses are repressed by background motion in a direction dependent manner, suggesting a control architecture in which target tracking and optomotor stabilization pathways operate in parallel during pursuit.echnology and Biological Sciences ResearchCouncil (BB/M011194/1

Performance and science reach of the Probe of Extreme Multimessenger Astrophysics for ultrahigh-energy particles

The Probe Of Extreme Multi-Messenger Astrophysics (POEMMA) is a potential NASA Astrophysics Probe-class mission designed to observe ultra-high energy cosmic rays (UHECRs) and cosmic neutrinos from space. POEMMA will monitor colossal volumes of the Earth's atmosphere to detect extensive air showers (EASs) produced by extremely energetic cosmic messengers: UHECRs above 20 EeV over the full sky and cosmic neutrinos above 20 PeV. We focus most of this study on the impact of POEMMA for UHECR science by simulating the detector response and mission performance for EAS from UHECRs. We show that POEMMA will provide a significant increase in the statistics of observed UHECRs at the highest energies over the entire sky. POEMMA will be the first UHECR fluorescence detector deployed in space that will provide high-quality stereoscopic observations of the longitudinal development of air showers. Therefore, it will be able to provide event-by-event estimates of the calorimetric energy and nuclear mass of UHECRs. The particle physics in the interactions limits the interpretation of the shower maximum on an event by event basis. In contrast, the calorimetric energy measurement is significantly less sensitive to the different possible final states in the early interactions. We study the prospects to discover the origin and nature of UHECRs using expectations for measurements of the energy spectrum, the distribution of arrival direction, and the atmospheric column depth at which the EAS longitudinal development reaches maximum. We also explore supplementary science capabilities of POEMMA through its sensitivity to particle interactions at extreme energies and its ability to detect ultra-high energy neutrinos and photons produced by top-down models including cosmic strings and super-heavy dark matter particle decay in the halo of the Milky Way.Comment: 40 pages revtex, with 42 figure

A virtual object point model for the calibration of underwater stereo cameras to recover accurate 3D information

The focus of this thesis is on recovering accurate 3D information from underwater images. Underwater 3D reconstruction differs significantly from 3D reconstruction in air due to the refraction of light. In this thesis, the concepts of stereo 3D reconstruction in air get extended for underwater environments by an explicit consideration of refractive effects with the aid of a virtual object point model. Within underwater stereo 3D reconstruction, the focus of this thesis is on the refractive calibration of underwater stereo cameras

Visual attention with implications for unilateral spatial neglect.

Recent models of visual attention (eg. Rizzolatti et al., 1987) have suggested that a similar system orients visual attention as is used to produce a saccadic eye movement. This thesis provides further support for the link between the attentional and eye orienting systems and has incorporated ideas from recent models of saccade generation. The time taken by normal subjects to initiate a saccade ('latency'), is examined in Chapters two, three and four. Subjects were given attentional instructions and saccades made to either: unilateral single, or, bilateral double, targets. Latency to attended targets was not greatly enhanced, while latency to non-attended targets was greatly slowed. The results support both the premotor model of visual attention and models of visual attention that emphasise the inhibitory consequence of directed attention. Bilateral double targets produced an additional slowing on saccade latency, which could reflect a further automatic attentional inhibition produced in the contralateral field by the stimulus onset. Fixation point offset (in 'gap' situations) is known to reduce saccade latency, which has been attributed to prior attentional disengagement (Fischer, 1987). In Chapter two, the use of a gap situation produced a generalised speeding which was independent of the effects of directed visual attention. This suggests that active fixation affects a separate component to that involved in orienting visual attention to a spatial location. This idea is incorporated into a model which emphasises the inhibitory consequences of attentive fixation. Chapters six and seven report the findings from an experimental investigation of a patient (B.Q.) with a 'unilateral spatial neglect', a condition often attributed to a deficit of visual attention. The 'gap' paradigm was shown to be effective at reducing the severity of B.Q.'s contralateral neglect. In contrast to normal subjects, bilateral double targets did not have an inhibitory effect on her saccade latency. These findings are explained in terms of a model that neglect results in part from the loss of attentional inhibition for the ipsilesional side of space and in part an inability to switch off contralesional inhibition produced during active fixation. A functional model is proposed in Chapter eight to account for the findings. This supports the close link between the attentional orienting and saccade programming systems. An additional implication of the findings is that models of visual attention and saccade generation need to consider the inhibitory consequences of directing attention to a spatial location

Aerospace Medicine and Biology: A continuing bibliography with indexes, supplement 165, March 1977

This bibliography lists 198 reports, articles, and other documents introduced into the NASA scientific and technical information system in February 1977