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Computerised diagnostic testing and computerised vision training (VT) have been developed for the orthoptic management of binocular vision (BV) anomalies in clinical practice. Computerised measurement of BV is assumed to assist accurate diagnosis of BV anomalies because variability of testing resulting from subjective judgements of examiners is eliminated by automatic measurements. Computerised VT is thought to be effective in the treatment of BV anomalies because the computer games used for vision training will enhance the patient's motivation. However, these assumptions were lacking scientific support. This thesis reports a range of studies to investigate the computerised programs of diagnostic testing (HTS-BVA) and vision training (HTS-iNet) in comparison with corresponding traditional approaches, respectively. The first study was to investigate inter-session repeatability of computerised testing on BV functions. The study results showed that computerised testing on measuring near horizontal fusional vergence (FV) and accommodative facility (AF) did not present higher inter-session repeatability than corresponding traditional testing. The second study was a pilot study for a future rigorous randomized clinical trial (RCT) investigating effectiveness of computerised VT as a home-based treatment for convergence insufficiency (CI). The study results showed the subjects with CI demonstrated improvement of near point of convergence (NPC), near base-out FV and symptoms associated with CI after an 8-week treatment regime. The third study, following from the first study, was to investigate whether accommodative responses (AR) are affected by the novel accommodative stimuli used in computerised AF testing. The study results showed the AR might be affected by the colours of accommodative targets and the colour filter used. Especially, the data of accommodative demand of 4 dioptres revealed that blue targets presented poorer AR than red targets, and the targets seen with colour filters presented poorer AR than those seen without colour filters. The fourth study, also following from the first study, was to investigate whether a prolonged near vision task affects measurements made relating to the near FV system, thus contributing to the variability of clinical findings. The study results showed statistically significant changes in NPC and near dissociated phoria. In further sub-group analyses, the subjects with an initially poor NPC (n = 9) presented greater changes in the NPC and near dissociated phoria than the subjects with normal poor NPC (n = 25).Overall, the computerised testing did not show more repeatable BV measurements than the traditional testing. Finally, an RCT is needed to determine if the computerised VT is more effective than placebo computerised VT as a home-based treatment for CI.

This thesis investigates the use of binocular information for motion-in-depth (MID) perception. There are at least two different types of binocular information available to the visual system from which to derive a perception of MID: changing disparity (CD) and inter-ocular velocity differences (IOVD). In the following experiments, we manipulate the availability of CD and IOVD information in order to assess the relative influence of each on MID judgements. In the first experiment, we assessed the relative effectiveness of CD and IOVD information for MID detection, and whether the two types of binocular information are processed by separate mechanisms with differing characteristics. Our results suggest that, both CD and IOVD information can be utilised for MID detection, yet, the relative dependence on either of these types of MID information varies between observers. We then went on to explore the contribution of CD and IOVD information to time-to-contact (TTC) perception, whereby an observer judges the time at which an approaching stimulus will contact them. We confirmed that the addition of congruent binocular information to looming stimuli can influence TTC judgements, but that there is no influence from binocular information indicating no motion. Further to this, we found that observers could utilise both CD and IOVD for TTC judgements, although once again, individual receptiveness to CD and/or IOVD information varied. Thus, we demonstrate that the human visual system is able to process both CD and IOVD information, but the influence of either (or both) of these cues on an individual’s perception has been shown to be mutually independent.

In the past decade, considerable attention has been paid to examination of the impact of amblyopia, and strabismus, upon the lives of the individuals. Although an extensive amount of literature exists regarding amblyopia and its associated visual defects, little is known about the contribution of the amblyopic eye in the habitual viewing condition (i.e. both eyes viewing). The purpose of these studies was to determine whether amblyopes are disadvantaged in the performance of tasks under habitual viewing conditions, highlighting any functional differences which may exist as a consequence of amblyopia. Secondly, the work aimed to investigate whether the amblyopic eye contributes to the habitual performance of these tasks. A simple light detection task, in a dichoptic arrangement based upon blue/yellow stimuli viewed through yellow filters, was used to investigate the above two aims and investigate the degree of interocular suppression in amblyopic participants. Using a 3D motion analysis system performance was assessed for an obstacle crossing task (adaptive gait) and a task of reaching for and grasping of an isolated object and in a 'cluttered' environment. Fine motor skills were assessed in a threading a needle task. On the whole it was found that amblyopes are not disadvantaged under habitual viewing conditions, and in cases where differences were found to exist this appeared to be in tasks requiring speed and accuracy. Consistently across all studies it was found that the amblyopic eye contributed in a positive manner, thus, as in visual normals, two eyes are better than one.

Impairment of stereoacuity is common in the elderly population and is found to be a risk factor for falls. The purpose of these experiments was to extend knowledge regarding impairment of binocular vision and adaptive gait. Firstly using a 3D motion analysis system to measure how impairment of stereopsis affected adaptive gait during a negotiation of a step, secondly by determining which clinical stereotest was the most reliable for measuring stereoacuity in elderly subjects and finally investigating how manipulating the perceived height of a step in both binocular and monocular conditions affected negotiation of a step. In conditions of impaired stereopsis induced by acutely presented monocular blur, both young and elderly subjects adopted a safety strategy of increasing toe clearance of the step edge, even at low levels of monocular blur (+0.50DS) and the effect was greater when the dominant eye was blurred. The same adaptation was not found for individuals with chronic monocular blur, where vertical toe clearance did not change but variability of toe clearance increased compared to full binocular correction. Findings indicate stereopsis is important for accurately judging the height of a step, and offers support to epidemiological findings that impaired stereoacuity is a risk for falls. Poor agreement was found between clinical stereotests. The Frisby test was found to have the best repeatability. Finally, a visual illusion that caused a step to be perceived as taller led to increased toe elevation. This demonstrates a potential way of increasing toe clearance when stepping up and hence increase safety on stairs.

Our eyes are horizontally separated in the head by approximately 6.5cm. As a result of this separation there are subtle differences in the position of corresponding image points within the two eyes. The horizontal component of this binocular positional difference is termed horizontal disparity. Horizontal disparity is an important visual cue as once scaled with an estimate of the viewing distance, it can theoretically provide full metric information about the structure of the world. This thesis will address the issue of how binocular visual cues are used by the human visual system for the estimation of three-dimensional (3-D) shape for perception and visuomotor control. The research presented is particularly focused on understanding why biases in the perception of 3-D shape from binocular cues are found, their importance for perception and visuomotor control and how these biases may be overcome by combining binocular cues with other sources of visual information.

When a line is slanted away from a binocular observer, the image of that line has different orientations on the two retinae. This difference has been called an orientation disparity. A mechanism that exploits the orientation disparities in the visual image could form an efficient method of signalling surface slant. Three different experimental techniques are employed here to investigate whether such a mechanism is exploited in the human, and non-human primate visual systems. Modelling The responses of early visual neurons were simulated using a two dimensional version of the disparity selective complex cell model of Ohzawa et al. (1990). This model had no specific mechanism for detecting orientation differences, and had poor sensitivity to slant. Despite this, the model was able to account for all previous physiological data (Blakemore et al., 1972; Nelson et al., 1977; Wieniawa-Narkiewicz et al., 1992). The model was used to generate predictions to enable new physiological recordings to determine whether or not there is a specialised neuronal mechanism that detects orientation differences. Single unit recording Significant differences in preferred monocular orientation were found in around 30% of the orientation selective neurons recorded from V1 in the two awake, behaving monkeys used for this study. When stimulated binocularly, about one third of the orientation selective V1 neurons appeared to respond consistently to the same interocular orientation difference as the monocular orientations were changed. However, rather than forming a population of neurons specifically selective for orientation differences, it is likely that this response was an artefact of not centering the stimulus on the receptive field of neurons tuned for positional disparity. Psychophysics The results of experiments presented here, combined with a critical review of previous psychophysical studies provide no evidence for an independent orientation disparity mechanism. None of the data presented here, using any of the above approaches, support a significant role for interocular orientation differences in the perception of slant.

The vergence and accommodation systems, which are examples of physiological control systems, enable us to acquire and maintain clear single images of objects at a variety of distances in our visual world. Vergence and accommodation systems are interact with one each other and have both visual and non-visual components thus adding to their complexity. This thesis reviews the evolution of control theory models of vergence and accommodation from the 1960's to the present day and has outlined several properties of the systems which require further study. The thesis introduces the concept of Fuzzy Logic Control (FLC) to models of oculomotor control. FLC offers a new approach to modelling natural control systems and produces more realistic models than those obtained using conventional control theory techniques. Several characteristics of the vergence and accommodation systems were investigated with the aim of incorporating experimental data into control theory models using conventional techniques and FLC. The accommodation response to anisometropic stimuli was measured objectively. No evidence of a non-consensual response was found, from which it can be concluded that accommodation is consensual. A control theory model of binocular accommodation was simulated to illustrate the control strategies adopted by the accommodation during anisometropic stimulation. A Virtual Reality (VR) stimulus was used to investigate the possibility of adaptation of the crosslink components of vergence and accommodation by placing different demands on the vergence and accommodation systems. Crosslink behaviour was altered as a result of the VR stimulus which suggests that the links between vergence and accommodation (accommodative vergence and vergence accommodation) are amenable to adaptation. Control theory models were used to illustrate the effects of the VR stimulus on vergence and accommodation. The effect of proximity was investigated by measuring accommodation responses in the presence and absence of proximal cues. The effect of proximal cues under closed loop conditions was found to be minimal which suggests that proximal cues are only effective when visual cues are reduced. The results were extended to include the vergence system and a FLC model of proximal vergence and accommodation was implemented. Simulation of the model produced similar findings to a previous study which supports the use of FLC in models of oculomotor control. Voluntary vergence and accommodation were measured objectively under open loop conditions in a group of naive subjects. All subjects were able to produce voluntary responses corresponding to near and far. The ability of subjects to distinguish intermediate distances was more varied. The results show that voluntary responses can be produced without training and it is suggested that voluntary vergence and accommodation may be an important mode of response. The results were included in a control model of voluntary vergence and accommodation using FLC. The work presented provides support for the use of Fuzzy Logic in models of oculomotor control which can be used to improve models and complement existing models using conventional techniques.

A model of stereopsis is proposed in which information from each eye's image is organised as a scale-based hierarchy before binocular comparison. The algorithm incorporates coarse-to-fine matching (like Marr and Poggio, 1979) but differs from previous models in that the position, and hence disparity, of features is defined relatively rather than by their retinal co-ordinate. Thus, fine scale disparities are measured and recorded relative to coarse scale disparities. Local surface slant and curvature is represented explicitly at a range of spatial scales. The theory is based on a hierarchical model of encoding position (Watt, 1988). The first experiment investigates the time course of shape discrimination in random dot stereograms. The results are compatible with a model in which the scale of analysis changes from coarse to fine over the first second of viewing. The second experiment measures the magnitude of a new "3-D" Müller-Lyer illusion and compares it to that of the classical (2-D) illusion. Both these and the cyclopean Müller-Lyer illusion are consistent with a model in which hierarchical encoding of position is used by the visual system for 2-D (length comparison) and 3-D (slant) judgements. The third experiment compares the detection of large disparities and large displacements. "Dmax" for the motion and stereo tasks is shown to be similar over a wide range of dot densities. The results are interpreted as evidence that similar spatial primitives are used in the correspondence process in both domains. The spacing of MIRAGE centroids (Watt and Morgan, 1985) fit the data well. The proposed hierarchical model is similar to that put forward by Mitchison and McKee (1987), although their scheme was not based on spatial scale. The model bridges the gap between a primal and a 2 1/2-D sketch (Marr, 1982) and has important implications for many issues within stereopsis.

Eye dominance is the preferential use of one eye over its companion to perform any given task. Eye dominance can broadly be classified into motor eye dominance (MED), also known as sighting dominance, and sensory eye dominance (SED), the eye with which an individual perceives more during binocular vision. However, it is not well understood how eye dominance affects the ability to accommodate in individuals with binocular vision dysfunction. Thus, the purpose of this study was to measure the accommodative responses of the dominant and non-dominant eye under different accommodative testing conditions using the Grand Seiko WAM-5500 Autorefractor. These accommodative test conditions were binocular, direct, and consensual. This study consisted of two visits, the first determining the clinical binocular status and symptoms of subjects. If subjects were determined to have binocular vision dysfunction based on clinical signs and/or symptoms, MED, SED, and accuracy of accommodation were assessed at the second visit. We found similar accuracy of accommodation between dominant and non-dominant eyes at all test conditions, but a significantly increased lag of accommodation in the consensual test condition compared to both binocular and direct conditions. This led us to conclude that accuracy of accommodation is not dependent on dominance of the eye, but whether the eye is viewing the target.

Tasks related to motion perception are some of the most frequent and important for surviving in a world filled with motion. Animals face tremendous evolutionary pressure to develop accurate systems for estimating the velocity of moving objects and predicting future trajectories. Motion detection and estimation were crucial for survival because they enabled animals to avoid being caught by predators and for predators to capture prey. Today, the visual system enables us to interact with the dynamic modern world we live in. Due to its clear evolutionary significance the study of motion has been common in vision science. Many prior studies have focused on two-dimensional (2D) motion perception and depth perception separately. Fewer studies have explicitly studied three-dimensional (3D) motion perception. This dissertation situates itself within a recent trend that focuses on the study of 3D motion by using a unified framework considering both motion and depth. I present two major projects that advance the study of 3D motion perception. First, I introduce novel stimuli that isolate the primary binocular cues to 3D motion. These novel stimuli allow for the characterization of two separate mechanisms that underlie the perception of motion-through-depth. I present two psychophysics experiments that use these stimuli to characterize the spatiotemporal properties of these mechanisms. In the second project, I extend the powerful continuous tracking paradigm to virtual reality (VR) to study the relative contribution of binocular and monocular cues to 3D motion. This chapter highlights the limitations of disparity processing and the contribution of monocular depth cues for a 3D motion tracking task. The work in this dissertation falls at a midpoint on the spectrum between traditional approaches to psychophysics and more recent developments using naturalistic stimuli and tasks. Taken together, the results described here advance what we know about binocular and monocular mechanisms for the perception of motion-through-depth. This work forms a foundation for testing how the primate visual system makes use of a variety of depth and motion cues to encode 3D motion. Future studies may further explore how coordination between the motion and motor systems enable us to interact with a dynamic 3D world

This study was undertaken to investigate ocular asymmetries in binocular vision using several dichoptic and binocular viewing paradigms. The literature on eye dominance was reviewed and it revealed that little emphasis both theoretically and experimentally had been placed on binocular viewing situations. The nature of the eye dominance tests and the dichotomous classification of the results suggested that one eye's image was competing against the other. The relationship between the different eye-dominance tests was not clear. A new approach to the study of ocular dominance has been developed in this thesis with specific attention to binocular vision and viewing situations. The term eye dominance has been replaced by the term ocular asymmetries to describe the results and measures derived from these procedures and the nature of the binocular visual approach. The experimental work is divided into three sections. Section one, is concerned with a binocular rivalry procedure using real images and afterimages. Section two, involves a stereoscopic viewing procedure and depth discrimination task with selective attenuation of the stereo-displays. Section three, investigates the interocular transfer of the spatial frequency shift. Measures of ocular asymmetry were derived, from all three procedures and the three sets of scores were positively related. This measure gives both the direction and the degree of the ocular asymmetry. The results indicate that ocular asymmetries are a valid feature of binocular vision. The new measure derived from the depth discrimination experiment provides a quantitative and consistent measure of ocular asymmetry. Special attention has been directed at the involvement of eye movements in all three paradigms and as the underlying factor in the asymmetry results. On the basis of the findings it was suggested that the asymmetry may reside in the binocular system controlling eye movements or reflect an asymmetry in processing speeds of the images from the two eyes arriving at the binocular site. The ocular asymmetry measures do not necessarily indicate eye movements are asymmetrical. It is recommended that ocular asymmetry is a variable to be studied in other investigations of binocular vision and binocular interactions.

Many theories have been proposed to explain why some otherwise intelligent children have unexpected problems with learning to read. In this thesis, evidence is presented -in support of the hypothesis that one cause of such children's difficulties is failure to develop accurate vergence eye movement control. This leads to impaired ability to localise small targets reliably, thus explaining the 'visual' nature of some of these children's reading problems. In 432 dyslexic and normal children vergence eye movements were recorded during the Dunlop Test of visual direction sense. Poor vergence eye movements were associated with variable ('unstable') responses in the Dunlop Test whilst good vergence control concorded with stable Dunlop Test responses. Further analysis showed that many dyslexic children were significantly impaired in several measures of vergence control when compared with either chronological or reading age matched controls. The parameters which distinguished most clearly between dyslexic and normal children's binocular control were found to be a target 1 degree of angular subtense moving at 0.6 degrees/second. A computer game was also developed to measure the accuracy of children's spatial localisation and to compare this with the results of the Dunlop Test. Children with unstable responses in the Dunlop Test were significantly worse in this test than children with stable responses. Overall, females were poorer at this test than males, with unstable females registering the lowest scores. A difference between the percentage error rate in the left and right hemifields was also shown. Females with unstable Dunlop Test responses were poorer than stable females in both visual fields, while unstable males made more errors than their stable counterparts only in the left visual field. These results provide confirmation of the hypothesis that females are less highly lateralised for visuospatial functions than males. A longitudinal study was carried out over 4 years on a cohort of 29 primary school children. The children were found to improve in the stability of their Dunlop Test responses, the stability of their vergence control and in their stereoacuity as they grew older. The children with unstable Dunlop Test responses and poor vergence control were found be significantly worse readers than those who showed good binocular control. Also children who took longer to develop stable responses to the Dunlop Test had poorer reading ability than those who developed good binocular control at an early age. The results are discussed in relation to a model of the development of reading ability and other postulated causes of reading difficulties. It is concluded that impaired vergence control may be associated with unreliable spatial localisation of words and letters. This is thought to be a sufficient cause for the difficulties some children show when learning to read, though it may often appear in combination with impaired linguistic skills.

The experience of stereovision is something that those of us who have it, can never image a life without it, but those who don’t have it, may become keenly aware that they are missing something else everyone has. The experience of stereovision has been overlooked – with some people arguing that it may not even be a necessary function. However, in this dissertation I show evidence that stereovision is important for everyday visuomotor tasks, those who have impaired stereovision show deficits in the motor movements most dependent on binocular vision and visual feedback. Indeed, the model that best predicts the relationship between stereoacuity and reaching-and-grasping movement kinematics is a linear sum of the peak velocity and the time it takes to for the grip. In particular, the time it takes to form the grip is a movement parameter that reflects the certainty of the intrinsic 3-dimensional properties of the target.In addition, a lifetime of experience with impaired stereovision does not result in functional adaptations in motor movement that are better than adaptations from people with stereo-loss in adulthood. But rather, the experience of stereovision seems to provide some benefit or stability when binocular vision is artificially disrupted. Furthermore, we provide evidence that stereovision can be strengthened in adulthood vis direct training using perceptual learning and scaffolding cues in virtual reality. We conclude that the experience of stereovision is indeed an important function in everyday visuomotor tasks and that direct stereo training can be a good tool restore stereovision in children and adults alike.

Forward facing eyes, which provide a wide field of binocular vision and precise depth perception, are one of the diagnostic features of crown primates. However, the adaptive significance of this feature remains contentious. Competing primate origins hypotheses variously propose that (1) foraging for fruit, (2) feeding on insects, and (3) leaping locomotion were responsible for the evolution of diagnostic primate traits, including forward facing eyes and a wide binocular visual field. This dissertation uses an experimental approach to improve our understanding of the evolution of this diagnostic primate trait. To evaluate which primate origins hypotheses provide a viable explanation for the evolution of primates’ forward facing orbits, the importance of binocular depth cues for the three tasks invoked by the hypotheses was evaluated experimentally in two species of lemurs considered reasonable living analogues of the earliest primates. Performance at fruit foraging, insect predation and leaping were evaluated when the animals had use of their full binocular visual field and when their binocular visual field was restricted using a helmet-mounted blinder. Restriction of the binocular field had no effect on fruit foraging performance. However, the restricted binocular field condition significantly decreased performance in both leaping and insect predation. Subjects leapt more slowly, restricted leaps to shorter distances and were more likely to exhibit adverse landings when their binocular field was restricted. Subjects were also significantly less likely to successfully contact and retrieve insect prey when their binocular field was restricted. Differences in behavioral variables also suggest that insect predation is a more visually demanding task than fruit foraging. These results support the role of both leaping and insect predation, but not fruit foraging, in contributing to the selective pressures that led to the evolution of forward facing eyes and a wide binocular field in crown primates.

Oyler School is located in one of the lowest socioeconomic areas in Cincinnati, Ohio. The OneSight Vision Center was established in 2012 to provide much needed eye care to children in Cincinnati. The purpose of this research study is to analyze the academic success of this group of inner-city students before and after receiving spectacle correction. In addition, the compliance rate of spectacle wear and a comparison of the IEP students to the non-IEP students from the Cincinnati school district are included. Eye examination records for 2,333 students were provided from 81 different schools in Cincinnati, which were all examined at the OneSight Vision Center during the 2012-2013 and 2013-2014 academic years. Analysis of the various eye examination components was conducted, and the data showed that many children from the clinic sample had myopia (37.2%), hyperopia (7.7%), and astigmatism (36.9%). In addition, many children exhibited phorias greater than 5pd (0.9%), strabismus (2.7%), convergence insufficiency (0.8%), and accommodative insufficiency (3.0%).All of the Oyler School students who received spectacles increased their average GPA by 0.14 points (p=0.17) two quarters after receiving spectacle correction. Myopes saw an increase in average GPA by 0.08 (p=0.50), hyperopes saw the greatest increase in GPA by 0.37 (p=0.34), and astigmats increased by 0.13 (p=0.45). Although none of these increases were statistically significant, a 0.37 increase in GPA two quarters after receiving vision correction is very meaningful. All groups of refractive error saw an increase in math and reading GPA scores, but not writing; however none of the changes were statistically significant. Large variability in GPA change and small sample sizes resulted in poor power (generally less than 20%) to detect statistically significant changes in our GPA scores.Only 28.9% of children who received glasses during the 2012-2013 school year wore their glasses to their 2013-2014 vison examination. The majority reported losing (53.1%) or breaking (34.6%) glasses. Non-compliant students had less refractive error (p=0.003) and were younger (p=0.05). When comparing the IEP student population to the non-IEP students from the overall OneSight Vision Center clinic population, 15.8% of IEP students had binocular visual acuity 20/40 or worse at near compared to 11.8% of the non-IEP students (X2, p=6 cm with 28.6% IEP students compared to 21.3% non-IEP students (X2, p

Humans and many animals have forward-facing eyes providing different views of the environment. Precise depth estimates can be derived from the resulting binocular disparities, but determining which parts of the two retinal images correspond to one another is computationally challenging. To aid the computation, the visual system focuses the search on a small range of disparities. Analysis of the statistics of natural scenes has revealed evidence that the brain exploits regularities to efficiently encode the visual world. We asked whether the brain similarly exploits the disparities encountered during binocular viewing of the natural environment. We did this by simultaneously measuring binocular eye position and 3D scene geometry during natural tasks using a novel device that can reconstruct a participant’s retinal image while they perform natural tasks such as socializing, navigating, and making a sandwich. We find that the natural distribution of disparities is indeed matched to the statistics of natural disparity, allowing for a smaller range of correspondence search. Furthermore, the distribution of disparity explains the perception of some ambiguous stereograms. Finally, disparity preferences of macaque cortical neurons are consistent with the natural distribution. Analysis of the disparities resulting from simulated eye positions yields notably different distributions, suggesting that models of disparity processing should carefully consider how assumptions about eye position could influence the results. We conclude that binocular neural processes are well-matched to the regularities of the 3D environment.

Stereoscopic 3D (S3D) displays offer the capability to enhance user performance on a variety of depth tasks. However, the benefit derived from viewing S3D depends in part on the magnitude of binocular disparity that is displayed. Surprisingly few studies have directly investigated the relationship between disparity and depth task performance. The studies that have been conducted suggest that a minimum amount of disparity (10-50 arc min) may be needed to improve performance over conditions in which no S3D is present, but it is unclear the extent to which performance might improve with increases in disparity beyond this range.From a human factors perspective, there are compelling reasons for using binocular disparities that are smaller than a strict geometrical interpretation of the scene would require (i.e., microstereopsis); one reason is to make the viewing experience more comfortable. This is important because S3D displays appear to cause a variety of simulator sickness-type problems for as many as 25-50% of users (including eye strain, headache, nausea, etc.). Preliminary evidence on the use of microstereopsis suggests that it does indeed result in a more comfortable and less fatiguing depth percept, particularly if binocular disparity is limited to a maximum of about 60 to 70 arc min (the One Degree Rule). But does microstereopsis also negate the performance benefits of stereopsis? How much can disparities be reduced before performance decrements are noticeable, and how comfortable are these disparities? Is there a stereo "sweet spot" in which both performance and comfort are high? And is this sweet-spot dependent on the particular depth task being tested?Results from a simple 2 degree-of-freedom (DOF) virtual precision object alignment task showed that when averaged across participants, maximum performance was achieved when disparity was limited to +/- 80 or 100 arc min of disparity during a 30 minute session. Performance with S3D cues improved alignment accuracy by up to 80% compared to no stereo cues, though several participants received an inconsistent benefit, and in a few cases, S3D resulted in detrimental performance. The tested magnitudes of disparity limits were also generally comfortable, although a significant correlation between increasing disparity and decreasing comfort was confirmed. Several optometric measures (e.g. stereoacuity, fusion ranges) predicted performance, but not comfort, on S3D displays.Results from a more complex 5 DOF virtual precision object alignment task showed that the best performance was achieved with disparity limits from +/- 60 to 100 arc min of disparity. Again, the tested magnitudes of disparity limits were generally comfortable, and several optometric measurements predicted performance but not comfort. Overall, the results suggest that the One Degree Rule for stereoscopic disparity limits can be expanded for near-viewing desktop applications. The results also suggest that while camera separations resulting in microstereopsis showed improved performance over no-stereopsis conditions, best performance is achieved with orthostereoscopic or near-orthostereoscopic levels of camera separation. The findings provide little support for Postural Instability Theory, but some support for Cue Conflict Theory, as useful guides for studying and mitigating viewer discomfort and simulator sickness symptoms on stereoscopic 3D display applications.

In binocular vision, performance may be superior or inferior to monocular performance depending upon the stimuli presented to each eye. In addition, monocular or binocular visual performance may be affected by the presence of features surrounding a target stimulus. The aim of this study was to investigate the impact of interocular stimulus similarities on a foveal acuity task in normally sighted children and adults. Liquid crystal shutter goggles synchronized with the monitor frame rate were used to present a Landolt C and surround bars to one or both eyes, in the following four viewing conditions. • Monocular: the Landolt C surrounded by bars was presented to the tested eye while the non-tested eye was occluded with a black opaque patch. • Binocular: the Landolt C surrounded by bars was presented to both eyes. • Dichoptic: the Landolt C was presented to the tested eye and flanking bars were presented to the non-tested eye. • Half-binocular: the Landolt C was presented to the tested eye and flanking bars were presented to both eyes. Discrimination of the orientation of a Landolt C was measured under each condition in 56 normally sighted children (7 to 14 years of age) and 22 adults (21 to 38 years of age). The effect of the surround bars (crowding) was tested in a subgroup of 9 children, and 10 adults. Across all age groups acuity was significantly better in the binocular condition than in the other three viewing conditions (binocular summation), and was significantly better in the half-binocular than in the dichoptic condition. In children, but not in adults, acuity was significantly better without than with bars. Interocular similarities may explain the enhanced visual acuity in the half-binocular condition in comparison with the dichoptic condition for all age groups tested. The results suggest that interocular interactions underpinning discrimination under these viewing conditions are developed in early childhood. The foveal crowding effect is immature at the beginning of school age, and maturation involves a reduction of this effect. These findings may have implications for the design of stimuli for binocular vision training therapies.

Accommodative insufficiency is a binocular vision disorder characterized by a decrease in age expected amplitudes of accommodation. This condition can result in symptoms of headaches, blurred vision and asthenopia. Vision therapy has been utilized in helping treat patients with accommodative insufficiency. The purpose of this study was to evaluate the repeatability of the Convergence Insufficiency Symptom Survey (CISS) in subjects with accommodative insufficiency. This study also examined the improvement in CISS scores following 8 weeks of weekly 1-hour office-based vision therapy with home reinforcement. Improvements in accommodation and vergence measures were also examined as part of this study. Subjects ages 9 to 30 were enrolled in the study. Measures of amplitudes of accommodation, accommodative facility, accommodative response, and vergence function were evaluated at baseline and were repeated following 8 weeks of vision therapy. Final outcome sensorimotor measures and CISS scores were collected by examiners masked to the subject’s progress and compliance with vision therapy. Using the method described by Bland-Altman, the CISS was found to be repeatable in subjects with accommodative insufficiency. The mean difference in scores between two administrations was 1.47 point with 95% limits of agreement of -5.19 and 8.13. Analysis using student’s t or the Wilcoxan sign rank test showed a statistically significant improvement in amplitudes of accommodation (AA) (p

In this dissertation, I examine binocular 3D motion processing through a series of psychophysical and neuroimaging experiments aimed at uncovering the neural computations involved and their interaction with the known hierarchy of visual motion processing. Two primary binocular cues could be used to compute 3D motion: one based on changing disparities over time (CD), the other based on interocular velocity differences (IOVD). Under normal viewing conditions, both cues coexist and (potentially) provide the same 3D direction information, yet whether CD, IOVD, or both mechanisms exist has distinct implications for how 3D motion is processed along the visual stream. First, I measured 3D direction discrimination sensitivity is measured for isolated binocular cues under a range of 3D motion speeds and visual eccentricities. Comparison of isolated-cue sensitivity to corresponding combined cue sensitivity (i.e. concurrent IOVD & CD cue stimuli) provided an estimate of relative cue contributions under normal viewing conditions. Second, I conducted a series of motion adaptation experiments to differentiate the neural representation of 2D and 3D directions of motion, and examine the degree to which IOVD or CD mechanisms can account for 3D motion adaptation. Third, I examined the neural locus of 3D motion processing by measuring 3D direction- selectivity throughout a range of visual cortical areas using functional neuroimaging in an event-related paradigm that parallels psychophysical adaptation experiments. Finally, I discuss the broader implications for the neural mechanisms of binocular 3D motion processing and future experimental directions. Together, these results reveal that: (1) the IOVD cue is the dominant cue to 3D motion processing across the majority of natural speeds & eccentricities, (2) neural tuning for 3D motion is distinct from 2D motion and can be fully explained by an IOVD mechanism, and (3) the IOVD cue is computed relatively late in the visual processing stream, in areas MT & MST— cortical areas primarily associated with 2D/retinal motion and thought to be beyond the point of binocular combination. The significance of IOVD —but not CD—cues to 3D motion perception motivates a drastic modification to canonical models of motion processing to include the late-stage comparison of eye- specific motion signals.

Determining the three-dimensional (3D) layout of the natural environment is an important but difficult visual function. It is difficult because the 3D layout of a scene and the shapes of 3D objects are not explicit in the 2D retinal images. The visual system uses both binocular (two eyes) and monocular (one eye) cues to determine 3D layout from these images. The same cues that are used to determine the layout of real scenes are also present in photographs and realistic pictures of 3D scenes. The work described in this dissertation examines how people perceive 3D layout in the natural environment and in pictures. Chapter 1 provides an introduction to the specific 3D cues that will be studied. Chapter 2 describes a series of experiments examining how the visual system's use of binocular cues might be adaptive to improve depth perception in the natural environment. Chapter 3 describes a series of experiments examining how the visual system interprets monocular linear perspective cues, and how this can lead to perceptual distortions in perceived 3D from pictures. Chapter 4, the Conclusion, discusses how the work described in this dissertation might be applied to creating better displays and pictures.

PURPOSE: To prospectively evaluate the effectiveness of home-based computer vergence therapy for treatment of binocular vision disorders in adults, ages 18-85, at least 3 months post brain injury. METHODS: Eligibility criteria included presence of binocular or accommodative dysfunction characterized by receded near point of convergence (NPC) (greater than or equal to 6 cm break), insufficient positive fusional vergence (PFV) at near (failing Sheard’s criterion or less than 15Δ blur or break), insufficient negative fusional vergence (NFV) at near (less than 12Δ blur or break), reduced vergence facility with 12ΔBO/3ΔBI at near (less than 15 cpm), and/or below minimum expected amplitude of accommodation for age. All subjects were prescribed 12 weeks of home-based computer vergence therapy. Phoria (cover test), NFV at near, PFV at near, NPC, vergence facility, accommodative amplitude and facility (nonpresbyopes only), and symptoms (convergence insufficiency symptom survey [CISS]) were assessed at baseline and after 4, 8 and 12 weeks of prescribed therapy. ANOVA was used to evaluate change in each measure. Percent successful also was determined. RESULTS: Of the 19 subjects enrolled (mean age 45.4 ± 12.9 years), 15 suffered external mechanical trauma to the head, 3 suffered cerebrovascular accident, and 1 suffered from organic brain syndrome. Six subjects were lost to follow-up. The binocular profile of the cohort at baseline was orthophoria (SD=1.08) at distance, 7.11Δ (SD=5.19) exophoria at near, NPC break = 17.07 cm (SD=10.56), NPC recovery = 21.48 cm (SD=11.66), near NFV = 12.33Δ (SD=4.37), near PFV = 8.80Δ (SD=5.69), vergence facility = 4.06 cpm (SD=4.41), and CISS = 31.12 (SD=12.93). ANOVA showed statistically significant improvement for NPC break (p=0.002) and recovery (p less than .001), PFV blur (p less than .0001), break (p less than .0001), and recovery (p less than .0001), NFV blur (p=0.047), break (p=0.008), and recovery (p=0.017), vergence facility (p less than .0001), and CISS (p less than .0001). The percentage of patients who were classified as “successful” or “improved” was 69% for NPC (less than 6 cm or a decrease of greater than 4 cm), 77% for PFV (greater than 15Δ and passing Sheard’s criterion or an increase of greater than or equal to 10Δ), 77% for NFV (greater than or equal to 12Δ or an increase of greater than or equal to 6Δ), 69% for PFV and NFV, 92% for vergence facility (15 cpm or an increase of 3 cpm), and 62% for CISS (less than 21 or a decrease of greater than or equal to 10 points).CONCLUSIONS: The majority of the 68% of subjects who completed the study experienced meaningful improvements in signs and symptoms.

The perceived relative direction of a pair of features can be intermediate between their relative direction in the two eyes. It is known that the perceived relative direction of the features can be altered by making their disparity gradient steep. Features at the edge between two surfaces at different depths form steep disparity gradients. These features are typically next to features on the same surface with the same disparity. These additional features were found to mitigate the effect of steep disparity gradients on perceived direction. The effect of the additional features was found to vary with their contrast, their contrast polarity and their separation relative to the features that define a steep disparity gradient. Hence, these stimulus properties determine whether disparity gradients affect the perceived direction of features at surface edges. That the perceived relative direction of a pair of features can be an average of the angles that they subtend at each eye supports the theory that perceived visual directions are referred to a point midway between the eyes (cyclopean eye). However, from this reference point, an occluding surface would hide features on the background that are visible to the left eye next to its left edge or visible to the right eye next to its right edge. Ono et. al. (2002) proposed that the perceived direction of these features is shifted laterally from their true direction when the occluder is fixated and the occluder is shifted in the opposite direction when the background is fixated. Erkelens et. al. (1996) proposed that the perceived direction of features is referred to the eye that views the monocular region instead of a cyclopean eye so that both surfaces may be perceived in their true direction. In the present study, two occluders were arranged so that a left side edge was physically aligned with a right side edge. The monocularly visible background texture next to these edges was also physically aligned. Consistent with the first proposal, the monocular regions or the edges of the occluders were found to appear laterally offset from one another indicating that their perceived direction was incorrect. Erkelens et. al. (1996) found that the perceived direction of the left and right edges of an occluding surface relative to a line on the background was found to be more strongly influenced by their position in the eye that views the monocular region of the background next to the edge than by their position in the other eye. In the present study, this Erkelens-bias was found with fixation on the background surface, but was not found with fixation on the occluder, which is also consistent with the first proposal. The Erkelens-bias decreased with the lateral separation of a target line on the occluder from its edge. The Erkelens-bias was found even when all texture on the surfaces was eliminated except for the outline of a foreground surface and a single line on the background surface. This indicates that the Erkelens-bias does not require the presence of either steep disparity gradients or monocular texture. The Erkelens-bias was eliminated by presenting the outline as the farthest feature in the stimulus, which is incompatible with it specifying the edges of a foreground surface.

The aim of this study was to add to our understanding of interocular interactions in normally sighted children (Group I, N=20), normal adults (Group II, N=20) and adults with anisometropic amblyopia (N=12) by investigating responses to a range of visual functions under three kinds of viewing condition. Visual functions tested were visual acuity, contrast sensitivity and alignment sensitivity. Stimuli were generated on a Cambridge VSG card driving a high resolution monitor and FE liquid crystal goggles, enabling three kinds of viewing conditions: 1. Monocular (non-tested eye occluded), used as a baseline for most functions. 2. Dichoptic (uniform field presented to the non-tested eye but with a binocular fusion lock). 3. Binocular. In general, binocular performance was better than monocular (binocular summation) but so too was dichoptic performance (dichoptic advantage). However there was much variation within individuals (the three functions showing different summation/advantage pattern) and between individuals. Significant conclusions include: (a) Maturational windows for interocular interactions differ for different spatial visual functions. (b) Interpretations of results from one visual function cannot be applied automatically to other functions. (c) Care must be taken in interpreting results based on 5 or fewer subjects.