Fixational eye movements in strabismic amblyopia

Purpose: To test the hypothesis that the fixational stability (FS) of the amblyopic eye (AME) in strabismics will improve when binocular integration is enhanced through ocular alignment and inter-ocular suppression is attenuated by reducing the contrast to the fellow eye (FFE). Methods: 7 strabismic amblyopes (age: 30.8±9.7 yrs) (5 esotropes and 2 exotrope) (VA: AME=0.50±0.30; FFE=-0.12±0.04) showing clinical characteristics of central suppression were recruited. Suppression was then attenuated by a balance point procedure where the contrast to the FFE was reduced in order to maximize binocular integration during a global motion task (GMT) (Baker, 2007). In one case the balance point could not be determined, and the participant was excluded. Ocular alignment was established with a haploscope. Participants dichoptically viewed similar targets [a cross (2.3°) surrounded by a square (11.3°) visual angle] set at 40cm. Target contrasts presented to each eye were either equal (EQ) or attenuated in the FFE (UNEQ) by an amount defined by the GMT. FS was measured over a 5 min period (Viewpoint® Eye Tracker, Arrington Research) and quantified using bivariate contour ellipse areas (BCEA) in four different binocular conditions; unaligned/EQ, unaligned/UNEQ, aligned/EQ and aligned/UNEQ. FS was also measured in 6 control subjects (Age: 25.3±4 yrs; VA: -0.1±0.08). Results: Alignment of the AME was transient and lasting between 30 to 80 seconds. Accordingly, FS was analyzed over the first 30 seconds using repeated measures ANOVA. Post hoc analysis revealed that for the amblyopic subjects, the FS of the AME was significantly improved in aligned/EQ (p=0.015) and aligned/UNEQ (p=0.001). FS of FFE was not different statistically across conditions. BCEA(FFE) & BCEA(AME) were then averaged for each amblyope in the 4 conditions and compared with normals. This averaged BCEA (reduced FS) was significantly greater (p=0.0205) in amblyopes compared to controls except in the case of alignment coupled with reduced suppression (aligned/UNEQ) (p=0.1232). Conclusion: Fixation stability in the amblyopic eye of strabismics appears to improve directly with the degree of binocular integration. The hypothesis is therefore retained

Haptic-Enhanced Learning in Preclinical Operative Dentistry

Background: Virtual reality haptic simulators represent a new paradigm in dental education that may potentially impact the rate and efficiency of basic skill acquisition, as well as pedagogically influence the various aspects of students’ preclinical experience. However, the evidence to support their efficiency and inform their implementation is still limited. Objectives: This thesis set out to empirically examine how haptic VR simulator (Simodont®) can enhance the preclinical dental education experience particularly in the context of operative dentistry. We specify 4 distinct research themes to explore, namely: simulator validity (face, content and predictive), human factors in 3D stereoscopic display, motor skill acquisition, and curriculum integration. Methods: Chapter 3 explores the face and content validity of Simodont® haptic dental simulator among a group of postgraduate dental students. Chapter 4 examines the predictive utility of Simodont® in predicting subsequent preclinical and clinical performance. The results indicate the potential utility of the simulator in predicting future clinical dental performance among undergraduate students. Chapter 5 investigates the role of stereopsis in dentistry from two different perspectives via two studies. Chapter 6 explores the effect of qualitatively different types of pedagogical feedback on the training, transfer and retention of basic manual dexterity dental skills. The results indicate that the acquisition and retention of basic dental motor skills in novice trainees is best optimised through a combination of instructor and visualdisplay VR-driven feedback. A pedagogical model for integration of haptic dental simulator into the dental curriculum has been proposed in Chapter 7. Conclusion: The findings from this thesis provide new insights into the utility of the haptic virtual reality simulator in undergraduate preclinical dental education. Haptic simulators have promising potential as a pedagogical tool in undergraduate dentistry that complements the existing simulation methods. Integration of haptic VR simulators into the dental curriculum has to be informed by sound pedagogical principles and mapped into specific learning objectives

Efficient rendering for three-dimensional displays

This thesis explores more efficient methods for visualizing point data sets on three-dimensional (3D) displays. Point data sets are used in many scientific applications, e.g. cosmological simulations. Visualizing these data sets in {3D} is desirable because it can more readily reveal structure and unknown phenomena. However, cutting-edge scientific point data sets are very large and producing/rendering even a single image is expensive. Furthermore, current literature suggests that the ideal number of views for 3D (multiview) displays can be in the hundreds, which compounds the costs. The accepted notion that many views are required for {3D} displays is challenged by carrying out a novel human factor trials study. The results suggest that humans are actually surprisingly insensitive to the number of viewpoints with regard to their task performance, when occlusion in the scene is not a dominant factor. Existing stereoscopic rendering algorithms can have high set-up costs which limits their use and none are tuned for uncorrelated {3D} point rendering. This thesis shows that it is possible to improve rendering speeds for a low number of views by perspective reprojection. The novelty in the approach described lies in delaying the reprojection and generation of the viewpoints until the fragment stage of the pipeline and streamlining the rendering pipeline for points only. Theoretical analysis suggests a fragment reprojection scheme will render at least 2.8 times faster than na\"{i}vely re-rendering the scene from multiple viewpoints. Building upon the fragment reprojection technique, further rendering performance is shown to be possible (at the cost of some rendering accuracy) by restricting the amount of reprojection required according to the stereoscopic resolution of the display. A significant benefit is that the scene depth can be mapped arbitrarily to the perceived depth range of the display at no extra cost than a single region mapping approach. Using an average case-study (rendering from a 500k points for a 9-view High Definition 3D display), theoretical analysis suggests that this new approach is capable of twice the performance gains than simply reprojecting every single fragment, and quantitative measures show the algorithm to be 5 times faster than a naïve rendering approach. Further detailed quantitative results, under varying scenarios, are provided and discussed

An assessment model and implementation of stereo image quality

In the past decade, many display hardware manufacturers have initiated research into the construction of stereo display devices. Currently, the use of such displays is limited to the computer-aided design; research, military and medical applications. However, it is anticipated that as display hardware becomes cheaper, gaming companies and desktop application software developers will realise the potential of using stereo to provide more realistic user experiences. To provide realistic stereo user experience it is necessary to utilise good quality stereo images in addition to suitable hardware. The growth of the Internet has resulted in an increase in the availability of stereo images. However, most have been captured using uncontrolled procedures and have questionable quality. The quality of stereo images is important since the viewing of poor quality stereo images can result in adverse viewing effects. A formal definition of stereo quality has not been achieved in current day research. This means that the factors which cause a stereo image to be perceived as poor quality have not been defined nor is a system available to detect its occurrence. This thesis attempts to address this problem by postulating a definition of stereo image quality based on detecting level of excess disparity levels, intensity differences and the occurrence of frame cancellation. An implementation system able to detect these identified factors is discussed and formulated. The developed system is utilised to test 14 stereo images of varying quality levels. The results of these tests are reported and are used to evaluated and refine the system. Using this image analysis, benchmarks for natural intensity difference in images, changes due to JPEG compression and comparisons with generated and ground truth disparity maps are formulated. Additionally, a

Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Exploring the optical perception of image within glass

Within the contemporary world, 3D film and television imagery is at the cutting edge of visual technology, but for centuries we have been captivated by the creation of visual illusions/allusions that play with our perception of the world, from the auto-stereoscopic barrier methods pioneered in the late 17th century by the French painter G. A. Bois-Clair to the ‘Op’ art movement of the 1960s and, more recently, Patrick Hughes’ ‘reverse perspective’ paintings. By building on these new and old technologies I have extended my own practice, which engages with the 2D image as a 3D allusion/illusion in glass, by examining how this type of image can be created and perceived within glass. I have explored theories of optical perception in connection with the binocular recognition of depth and space, as well as kinetic clues to distance through motion parallax monitoring and assumptions about default linear perspective, light and inference within our personal schemata. - ‘Optical illusion’ is used to mean an instance of a wrong or misinterpreted perception of a sensory experience; the distortion of senses revealing how the brain organises and interprets visual information; an individual’s ability to perceive depth, 3D form and motion. - ‘Allusion’ is used to imply a symbolic or covert reference. My practical research focuses on the perceived creation of the 3D image within glass and explores the notion of glass as a facilitator in working with and challenging the themes of 3D image perception. I have particularly addressed artistic spatial illusionary methods, reverse perspective techniques, auto-stereoscopic image-based systems, parallax stereograms and lenticular print and lens technology. Through building on my previous practice of working with multiple-layered images within cast glass, combined with more complex and scientific optical methods, I have explored the perception of the image by working with new and old 3D technologies in order to produce a body of work which examines this perception within glass. During my research I have developed an original casting process, a vacuum-casting lost wax process for glass, in addition to producing an accurate industry standard lenticular glass lens. This research intends to provide a theoretical basis for new glass working techniques, both within the glass artist’s studio and in the commercial world of print, towards applications within architectural design, installation art and image-based artwork in general. This thesis is therefore a summation of the research that I have undertaken over the past six years and an attempt to give substance to the ideas and references that have preoccupied my own investigations over that period. I have structured the thesis into three themes: perspective; perception; and process but those three elements were never separate from each other and not only do they depend on each other, their purpose is, in some way, to combine in the creation of my finished pieces

Phase relationships in stereoscopic computation

We apply the notion that phase differences can be used to interpret disparity between a pair of stereoscopic images. Indeed, phase relationships can also be used to obtain orientation and probabilistic measures from both edges and comers, as well as the directional instantaneous frequency of an image field. The method of phase differences is shown to be equivalent to a Newton-Raphson root finding iteration through the resolutions of band-pass filtering. The method does, however, suffer from stability problems, and in particular stationary phase. The stability problems associated with this technique are implicitly derived from the mechanism used to interpet disparity, which in general requires an assumption of linear phase and the local instantaneous frequency. We present two techniques. Firstly, we use the centre frequency of the applied band-pass filter to interpret disparity. This interpretation, however, suffers heavily from phase error and requires considerable damping prior to convergence. Secondly, we use the derivative of phase to obtain the instantaneous frequency from an image, which is then used to improve the disparity estimate. The second measure is implicitly sensitive to regions that exhibit stationary phase. We prove that stationary phase is a form of aliasing. To maintain stability with this technique, it is essential to smooth the disparity signal at each resolution of filtering. These ideas are extended into 2-D where it is possible to extract both vertical and horizontal disparities. Unfortunately, extension into 2-D also introduces a similar form of the motion aperture problem. The best image regions to disambiguate both horizontal and vertical disparities lie in the presence of comers. Fortunately, we introduce a measure for identifying orthogonal image signals based upon the same filters that we use to interpret disparity. We find that in the presence of dominant edge energy, there is an error in horizontal disparity interpretation that varies as a cosine function. This error can be reduced by iteration or resolving the horizontal component of the disparity signal. These ideas are also applied towards the computation of deformation, which is related to the magnitude and direction of surface slant. This is a natural application to the ideas presented in this thesis

From local constraints to global binocular motion perception

Humans and many other predators have two eyes that are set a short distance apart so that an extensive region of the world is seen simultaneously by both eyes from slightly different points of view. Although the images of the world are essentially two-dimensional, we vividly see the world as three-dimensional. This is true for static as well as dynamic images. We discuss local constraints for the perception of three-dimensional binocular motion in a geometric-probabilistic framework. It is shown that Bayesian models of binocular 3D motion can explain perceptual bias under uncertainty and predict perceived velocity under ambiguity. The models exploit biologically plausible constraints of local motion and disparity processing in a binocular viewing geometry. Results from psychophysical experiments and an fMRI study support the idea that local constraints of motion and disparity processing are combined late in the visual processing hierarchy to establish perceived 3D motion direction. The methods and results reported here are likely to stimulate computational, psychophysical, and neuroscientific research because they address the fundamental issue of how 3D motion is represented in the human visual system

Stereoscopic 3D user interfaces : exploring the potentials and risks of 3D displays in cars

During recent years, rapid advancements in stereoscopic digital display technology has led to acceptance of high-quality 3D in the entertainment sector and even created enthusiasm towards the technology. The advent of autostereoscopic displays (i.e., glasses-free 3D) allows for introducing 3D technology into other application domains, including but not limited to mobile devices, public displays, and automotive user interfaces - the latter of which is at the focus of this work. Prior research demonstrates that 3D improves the visualization of complex structures and augments virtual environments. We envision its use to enhance the in-car user interface by structuring the presented information via depth. Thus, content that requires attention can be shown close to the user and distances, for example to other traffic participants, gain a direct mapping in 3D space