Occlusion-related lateral connections stabilize kinetic depth stimuli through perceptual coupling

Local sensory information is often ambiguous forcing the brain to integrate spatiotemporally separated information for stable conscious perception. Lateral connections between clusters of similarly tuned neurons in the visual cortex are a potential neural substrate for the coupling of spatially separated visual information. Ecological optics suggests that perceptual coupling of visual information is particularly beneficial in occlusion situations. Here we present a novel neural network model and a series of human psychophysical experiments that can together explain the perceptual coupling of kinetic depth stimuli with activity-driven lateral information sharing in the far depth plane. Our most striking finding is the perceptual coupling of an ambiguous kinetic depth cylinder with a coaxially presented and disparity defined cylinder backside, while a similar frontside fails to evoke coupling. Altogether, our findings are consistent with the idea that clusters of similarly tuned far depth neurons share spatially separated motion information in order to resolve local perceptual ambiguities. The classification of far depth in the facilitation mechanism results from a combination of absolute and relative depth that suggests a functional role of these lateral connections in the perception of partially occluded objects

Object-based 2D-to-3D video conversion for effective stereoscopic content generation in 3D-TV applications

Three-dimensional television (3D-TV) has gained increasing popularity in the broadcasting domain, as it enables enhanced viewing experiences in comparison to conventional two-dimensional (2D) TV. However, its application has been constrained due to the lack of essential contents, i.e., stereoscopic videos. To alleviate such content shortage, an economical and practical solution is to reuse the huge media resources that are available in monoscopic 2D and convert them to stereoscopic 3D. Although stereoscopic video can be generated from monoscopic sequences using depth measurements extracted from cues like focus blur, motion and size, the quality of the resulting video may be poor as such measurements are usually arbitrarily defined and appear inconsistent with the real scenes. To help solve this problem, a novel method for object-based stereoscopic video generation is proposed which features i) optical-flow based occlusion reasoning in determining depth ordinal, ii) object segmentation using improved region-growing from masks of determined depth layers, and iii) a hybrid depth estimation scheme using content-based matching (inside a small library of true stereo image pairs) and depth-ordinal based regularization. Comprehensive experiments have validated the effectiveness of our proposed 2D-to-3D conversion method in generating stereoscopic videos of consistent depth measurements for 3D-TV applications

Apparent Opacity Affects Perception of Structure from Motion

The judgment of surface attributes such as transparency or opacity is often considered to be a higher-level visual process that would make use of low-level stereo or motion information to tease apart the transparent from the opaque parts. In this study, we describe a new illusion and some results that question the above view by showing that depth from transparency and opacity can override the rigidity bias in perceiving depth from motion. This provides support for the idea that the brain's computation of the surface material attribute of transparency may have to be done either before, or in parallel with the computation of structure from motion

3D computational modeling and perceptual analysis of kinetic depth effects

Humans have the ability to perceive kinetic depth effects, i.e., to perceived 3D shapes from 2D projections of rotating 3D objects. This process is based on a variety of visual cues such as lighting and shading effects. However, when such cues are weak or missing, perception can become faulty, as demonstrated by the famous silhouette illusion example of the spinning dancer. Inspired by this, we establish objective and subjective evaluation models of rotated 3D objects by taking their projected 2D images as input. We investigate five different cues: ambient luminance, shading, rotation speed, perspective, and color difference between the objects and background. In the objective evaluation model, we first apply 3D reconstruction algorithms to obtain an objective reconstruction quality metric, and then use quadratic stepwise regression analysis to determine weights of depth cues to represent the reconstruction quality. In the subjective evaluation model, we use a comprehensive user study to reveal correlations with reaction time and accuracy, rotation speed, and perspective. The two evaluation models are generally consistent, and potentially of benefit to inter-disciplinary research into visual perception and 3D reconstruction

Stereoscopic Surface Interpolation from Illusory Contours

Stereoscopic Kanizsa figures are an example of stereoscopic interpolation of an illusory surface. In such stimuli, luminance-defined disparity signals exist only along the edges of inducing elements, but observers reliably perceive a coherent surface that extends across the central region in depth. The aim of this series of experiments was to understand the nature of the disparity signal that underlies the perception of illusory stereoscopic surfaces. I systematically assessed the accuracy and precision of suprathreshold depth percepts using a collection of Kanizsa figures with a wide range of 2D and 3D properties. For comparison, I assessed similar perceptually equated figures with luminance-defined surfaces, with and without inducing elements. A cue combination analysis revealed that observers rely on ordinal depth cues in conjunction with stereopsis when making depth judgements. Thus, 2D properties (e.g. occlusion features and luminance relationships) contribute rich information about 3D surface structure by influencing perceived depth from binocular disparity

Analyzing interfaces and workflows for light field editing

With the increasing number of available consumer light field cameras, such as Lytro, Raytrix, or Pelican Imaging, this new form of photography is progressively becoming more common. However, there are still very few tools for light field editing, and the interfaces to create those edits remain largely unexplored. Given the extended dimensionality of light field data, it is not clear what the most intuitive interfaces and optimal workflows are, in contrast with well-studied two-dimensional (2-D) image manipulation software. In this work, we provide a detailed description of subjects' performance and preferences for a number of simple editing tasks, which form the basis for more complex operations. We perform a detailed state sequence analysis and hidden Markov chain analysis based on the sequence of tools and interaction paradigms users employ while editing light fields. These insights can aid researchers and designers in creating new light field editing tools and interfaces, thus helping to close the gap between 4-D and 2-D image editing

Augmented reality X-ray vision on optical see-through head mounted displays

Abstract. In this thesis, we present the development and evaluation of an augmented reality X-ray system on optical see-through head-mounted displays. Augmented reality X-ray vision allows users to see through solid surfaces such as walls and facades, by augmenting the real view with virtual images representing the hidden objects. Our system is developed based on the optical see-through mixed reality headset Microsoft Hololens. We have developed an X-ray cutout algorithm that uses the geometric data of the environment and enables seeing through surfaces. We have developed four different visualizations as well based on the algorithm. The first visualization renders simply the X-ray cutout without displaying any information about the occluding surface. The other three visualizations display features extracted from the occluder surface to help the user to get better depth perception of the virtual objects. We have used Sobel edge detection to extract the information. The three visualizations differ in the way to render the extracted features. A subjective experiment is conducted to test and evaluate the visualizations and to compare them with each other. The experiment consists of two parts; depth estimation task and a questionnaire. Both the experiment and its results are presented in the thesis

A border-ownership model based on computational electromagnetism

The mathematical relation between a vector electric field and its corresponding scalar potential field is useful to formulate computational problems of lower/middle-order visual processing, specifically related to the assignment of borders to the side of the object: so-called border ownership (BO). BO coding is a key process for extracting the objects from the background, allowing one to organize a cluttered scene. We propose that the problem is solvable simultaneously by application of a theorem of electromagnetism, i.e., “conservative vector fields have zero rotation, or “curl.” We hypothesize that (i) the BO signal is definable as a vector electric field with arrowheads pointing to the inner side of perceived objects, and (ii) its corresponding scalar field carries information related to perceived order in depth of occluding/occluded objects. A simple model was developed based on this computational theory. Model results qualitatively agree with object-side selectivity of BO-coding neurons, and with perceptions of object order. The model update rule can be reproduced as a plausible neural network that presents new interpretations of existing physiological results. Results of this study also suggest that T-junction detectors are unnecessary to calculate depth order

Feature specific segmentation in perceived structure-from-motion

AbstractMotion information is important to vision for extracting the 3-D (three-dimensional) structure of an object, as evidenced by the compelling percept of three-dimensionality attainable in displays which are purely motion-defined. It has recently been shown that when subjects view a rotating transparent cylinder of dots simulated with parallel projection, they rarely perceive rotation reversals which are physically introduced (Treue, Andersen, Ando & Hildreth, Vision Research, 35;1995:139–148). We show however that when the elements defining the cylinder are oriented, the number of perceived reversals increases systematically to near maximum as the difference between element orientations on the two surfaces increases. These results imply that structure-from-motion mechanisms are capable of exploiting local feature differences between the different surfaces of a moving object

Key characteristics of specular stereo.

Because specular reflection is view-dependent, shiny surfaces behave radically differently from matte, textured surfaces when viewed with two eyes. As a result, specular reflections pose substantial problems for binocular stereopsis. Here we use a combination of computer graphics and geometrical analysis to characterize the key respects in which specular stereo differs from standard stereo, to identify how and why the human visual system fails to reconstruct depths correctly from specular reflections. We describe rendering of stereoscopic images of specular surfaces in which the disparity information can be varied parametrically and independently of monocular appearance. Using the generated surfaces and images, we explain how stereo correspondence can be established with known and unknown surface geometry. We show that even with known geometry, stereo matching for specular surfaces is nontrivial because points in one eye may have zero, one, or multiple matches in the other eye. Matching features typically yield skew (nonintersecting) rays, leading to substantial ortho-epipolar components to the disparities, which makes deriving depth values from matches nontrivial. We suggest that the human visual system may base its depth estimates solely on the epipolar components of disparities while treating the ortho-epipolar components as a measure of the underlying reliability of the disparity signals. Reconstructing virtual surfaces according to these principles reveals that they are piece-wise smooth with very large discontinuities close to inflection points on the physical surface. Together, these distinctive characteristics lead to cues that the visual system could use to diagnose specular reflections from binocular information.The work was funded by the Wellcome Trust (grants 08459/Z/07/Z & 095183/Z/10/Z) and the EU Marie Curie Initial Training Network “PRISM” (FP7-PEOPLE-2012-ITN, Agreement: 316746).This is the author accepted manuscript. The final version is available from ARVO via http://dx.doi.org/10.1167/14.14.1