Stereopsis is a par excellence demonstration of the computational power that neural systems can encapsulate. How is the brain capable of swiftly transforming a stream of binocular two-dimensional signals into a cohesive three-dimensional percept? Many brain regions have been implicated in stereoscopic processing, but their roles remain poorly understood. This dissertation focuses on the contributions of primary and dorsomedial visual cortex. Using convolutional neural networks, we found that disparity encoding in primary visual cortex can be explained by shallow, feed-forward networks optimized to extract absolute depth from naturalistic images. These networks develop physiologically plausible receptive fields, and predict neural responses to highly unnatural stimuli commonly used in the laboratory. They do not necessarily relate to our experience of depth, but seem to act as a bottleneck for depth perception. Conversely, neural activity in downstream specialized areas is likely to be a more faithful correlate of depth perception. Using ultra-high field functional magnetic resonance imaging in humans, we revealed systematic and reproducible cortical organization for stereoscopic depth in dorsal visual areas V3A and V3B/KO. Within these regions, depth selectivity was inversely related to depth magnitude — a key characteristic of stereoscopic perception. Finally, we report evidence for a differential contribution of cortical layers in stereoscopic depth perception.

Most computational theories of stereopsis require a registration stage prior to stereo matching to reduce the matching to a one-dimensional search. Even after registration, it is critical that the stereo matching process tolerate some degree of residual misalignment. In this paper, we study with psychophysical techniques the tolerance to vertical disparity in situations in which false targets abound ?? in random dot stereograms ??d eye movements are eliminated. Our results show that small amounts of vertical disparity significantly impair depth discrimination in a forced-choice task. Our main results are: a) vertical disparity of only the central "figure" part of a random dot stereogram can be tolerated up to about 3.5', b) vertical disparity of the "figure + ground" is tolerated up to about 6.5', and c) the performance of the Grimson implementation of the Marr-Poggio stereo matching algorithm for the stereograms of experiment (a) is consistent with the psychophysical results. The algorithm's tolerance to vertical disparity is due exclusively to the spatial averaging of the underlying filters. The algorithm cannot account by itself for the results of experiment (b). Eye movements, which are the principal registration mechanism for human stereopsis, are accurate to within about 7'. Our data suggest that tolerance to this residual vertical disparity is attained by two non-motor mechanisms: 1) the spatial average performed by the receptive fields that filter the two images prior to stereo matching, and 2) a non-motor shift mechanism that may be driven at least in part by monocular cues.

In this dissertation, we conducted a stereoscopic eye tracking experiment using naturalistic stereo images. We analyzed low level 2D and 3D scene features at binocular fixations and randomly selected places. The results reveal that humans tend to fixate on regions with higher luminance variations, but lower disparity variations. Because of the often observed co-occurrence of luminance and depth changes in natural environments, the dichotomy between luminance features and disparity features inspired us to study the accurate statistics of 2D and 3D scene properties. Using a range map database, we studied the distribution of disparity in natural scenes. The natural disparity distribution has a high peak at zero, and heavier tails that are similar to a Laplace distribution. The relevance of natural disparity distribution to other studies in neurobiology and visual psychophysics are discussed in detail. We also studied luminance, range and disparity statistics in natural scenes using a co-registered luminance-range database. The distributions of bandpass 2D and 3D scene features can be well modeled by generalized Gaussian models. There are positive correlations between bandpass luminance and depth, which can be captured by varying shape parameters in the probability density functions of the generalized Gaussians. In another study on suprathreshold luminance and depth discontinuities, we show that observing a significant luminance edge at a significant depth edge is much more likely than at homogeneous depth surfaces. It is also true that a significant depth edge happens at a significant luminance edge with a greater probability than at homogeneous luminance regions. Again, the dependency between luminance and depth discontinuities can be modeled successfully by generalized Gaussians. We applied our statistical models in 3D natural scenes to stereo correspondence. A Bayesian framework is proposed to incorporate the bandpass disparity prior, and the luminance-disparity dependency in the likelihood function. We compared our algorithm with a classical simulated annealing method based on heuristically defined energy functions. The computed disparity maps show great improvements both perceptually and objectively. / text

No / Falls in the elderly are a major cause of serious injury and mortality. Impaired and absent stereopsis may be a significant risk factor for falls or hip fracture, although data from epidemiological studies are not consistent. Previous laboratory based studies, however, do suggest that stereoacuity is an important factor in adaptive gait. The present study investigates how acute impairment of stereopsis, through monocular blur of differing levels, ranging from 0.50 diopter (D) to a monovision correction affected gait when negotiating a raised surface in elderly subjects. Eleven elderly subjects (73.3 3.6 years) walked up to and negotiated a raised surface under nine visual conditions, binocular vision, one eye occluded and 0.50 D, 1.00 D and monovision correction (mean 2.50 D 0.20 D) with blur and occlusion either over the dominant or non-dominant eye. Analysis focused on foot positioning and toe clearance parameters. There was no effect of ocular dominance on any parameters. Monocular blur impaired stereopsis (p 0.01), with more minor effects on high and low contrast acuity. Vertical and horizontal lead limb toe clearance both increased under all levels of monocular blur including the lowest level of 0.50 DBlur (p 0.03) and monovision correction led to toe clearance levels similar to that found with occlusion of one eye. Findings demonstrated that even small amounts of monocular blur can lead to a change in gait when negotiating a raised surface, suggesting acute monocular blur affected the ability to accurately judge the height of a step in the travel path. Further work is required to investigate if similar adaptations are used by patients with chronic monocular blur.

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.

No description available.

Stereopsis is the process of inferring the distance to objects from two or more images. It has applications in areas such as: novel-view rendering, motion capture, autonomous navigation, and topographical mapping from remote sensing data. Although it sounds simple, in light of the effortlessness with which we are able to perform the task with our own eyes, a number of factors that make it quite challenging become apparent once one begins delving into computational methods of solving it. For example, occlusions that block part of the scene from being seen in one of the images, and changes in the appearance of objects between the two images due to: sensor noise, view dependent effects, and/or differences in the lighting/camera conditions between the two images. Global stereopsis algorithms aim to solve this problem by making assumptions about the smoothness of the depth of surfaces in the scene, and formulating stereopsis as an optimization problem. As part of their formulation, these algorithms include a function that measures the similarity between pixels in different images to detect possible correspondences. Which of these match cost functions work better, when, and why is not well understood. Furthermore, in areas of computer vision such as segmentation, face detection, edge detection, texture analysis and classification, and optical flow, it is not uncommon to use colour spaces other than the well known RGB space to improve the accuracy of algorithms. However, the use of colour spaces other than RGB is quite rare in stereopsis research. In this dissertation we present results from two, first of their kind, large scale studies on global stereopsis algorithms. In the first we compare the relative performance of a structured set of match cost cost functions in five different global stereopsis frameworks in such a way that we are able to infer some general rules to guide the choice of which match cost functions to use in these algorithms. In the second we investigate how much accuracy can be gained by simply changing the colour representation used in the input to global stereopsis algorithms.

Syfte: I denna litteraturstudie var syftet att undersöka potentiella amblyopibehandlingar samt deras effektivitet utifrån kliniska studier. Metod: Avancerade sökningar gjordes i PubMed mellan 16 och 19 april 2023. Inklusionskraven för denna litteraturstudie var att det var en klinisk studie, studien fanns i fulltext, språket var svenska eller engelska samt att de publicerades mellan årtalen 2000 och 2023. Kraven för relevant innehåll var att det handlade om behandlingsalternativ för amblyopi som inte vanligtvis används i vården idag. Studier som inte uppfyllde kraven om relevant innehåll exkluderades. Resultat: 42 studier granskades med sex identifierade kategorier av behandlingsalternativ: dichoptic binocular training, akupunktur, farmakologi, perceptuell inlärning, aktiv monokulär terapi och low-level laser therapy. Effektiviteten av behandlingarna varierar starkt mellan kategorierna. Av de granskade är dichoptic binocular training mest sannolik att användas som komplement till vedertagen behandling. Slutsats: Inga av dessa amblyopi behandlingar kan ersätta vedertagen behandling. Det är mer sannolikt att vissa av dem kan användas som komplement efter att fler kliniska prövningar utförts och metodiken fastställts. / Aim: The aim of this literature study was to investigate novel amblyopia treatments and their effectiveness based on clinical studies. Method: The literature study is based on PubMed searches made between the 16th and 19th of April 2023. The inclusion criteria of the reviewed studies were as follows: it was a clinical trial, available in full text, in Swedish or English, published between 2000 and 2023, and had relevant content. To be included as relevant content, the study had to be discussing treatment options not used in healthcare as a treatment option outside of clinical trials. Studies that did not fulfil the criteria of relevance were excluded.   Result: Forty-two studies were reviewed with six identified categories of non-conventional treatment options: dichoptic binocular training, acupuncture, pharmacological, perceptual learning, active monocular therapy, and low-level laser therapy. The effectiveness of the treatments varies greatly between the categories. Of the reviewed studies, dichoptic binocular training is most likely to be used as an adjunct to treatments that are already established. Conclusion: Despite the fact that many trials have shown positive results in terms of improvement in visual acuity, none of them seem promising enough to replace current treatments such as occlusion due to mixed results with respect to amblyopia resolution and long-term maintenance of the improved acuity. Some of these solutions are more likely to be available and used as a complement or in situations where established treatments are no longer working. Before they may be regarded as having potential for use in treatment, more clinical trials and studies are required in each area examined.

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.

Yes / Purpose: The purpose of this study was to develop a convenient test of stereopsis in the clinic that is both robust and reliable and capable of providing a measure of variability necessary to make valid comparisons between measurements obtained at different occasions or under different conditions. Methods: Stereo acuity was measured based on principles derived from the laboratory measurement of stereopsis (i.e., staircase method). Potential premeasurement compensations are described if there is a significant degree of ocular misalignment, reduced visual acuity, or aniseikonia. Forty-six adults at McGill University, 44 adults at Auckland University, and 51 adults from the University of Bradford, with an age range of 20 to 65 years old and normal or corrected-to-normal vision participated in this study. Results: Stereo acuity within this normal population was widely distributed, with a significant percentage (28%) of the population with only coarse stereo (>300 arc seconds). Across subjects, the SD was approximately 25% of the mean. Measurements at two different times were strongly (r = 0.79) and significantly (P < 0.001) correlated, with little to no significant (P = 0.79) bias (0.01) between test and retest measures of stereopsis. Conclusions: The application enables measurements over the wide disparity range and not just at the finest disparities. In addition, it allows changes in stereopsis of the order of 1.9 to be statistically distinguished.