Spotlight: Recent Research

This page highlights selected research by our Vision Science faculty, professional staff, postdoctoral fellows, and graduate students. The selections will change regularly, so be sure to visit often!

Research by Recent Graduates

Tandra Ghose, PhD

Title
Extremal Edges: A Powerful Cue to Depth and Figure-Ground Organization

Abstract
Extremal edges (EEs) are viewpoint-specific tangent points of self-occlusion on smoothly curved, convex surfaces. A simple ecological analysis of viewpoint constraints shows that the curved surface producing an EE is likely to be closer to the observer than the surface on the other, non-EE side. Four experiments examined whether EEs and 3D surface convexity operate as cues to depth and figure-ground organization. Experiment 1 used simple luminance profiles (the positive half of a sinusoid) to simulate shading gradients in simple bipartite displays. The results showed that observers are very likely to perceive EEs as closer and figural, and that EEs are more potent than surface convexity alone. Because the argument from general viewpoint is strictly about the geometry of the scene, independent of the kind of visual information that specifies the existence of an extremal edge, it follows that the bias toward perceiving EE surfaces as closer should hold regardless of what visual property specifies the extremal edge. To test this hypothesis, Experiment 2 used EEs rendered via texture gradients of checkerboard surfaces that contained neither shading and nor occlusion cues. The results of this experiment showed a strong bias toward perceiving the EE side as closer and figural from texture gradients. Experiment 3 used ray-traced images of EE shading patterns on simple convex "pillow-like" surfaces to study the combination of EEs with Gestalt cues of smaller size and 2D edge convexity. EEs largely dominated the other figural cues (2D edge convexity, size, and their combination) studied in this experiment. Experiment 4 used shading gradients in ray-traced images of surfaces of revolution to study the effects of EEs versus other individual figure-ground cues (region size, 2D edge convexity, surroundedness, and familiarity). The results show that EEs produce stronger effects than all of these factors. The data clearly demonstrate that extremal edges are among the most powerful cues to depth across a contour and to figure-ground organization.

 Poster
 Web page

Ahna Girshick, PhD

Title
Probabilistic integration of sensory information for 3D visual surface slant perception

Abstract
Human depth perception involves combining multiple, possibly conflicting, sensory measurements. Previous work with slightly conflicting cues has shown that this process is performed by statistical optimal weighted averaging. Here we ask whether the perceptual system has a mechanism to be robust to large cue conflicts. We investigated how binocular disparity and texture are combined in estimating slant as a function of their conflict. When the two cues only had a small conflict, we found evidence for optimally weighted averaging. At larger conflicts, we observed robust behavior in which one of the discrepant cues was rejected. Interestingly, the ignored cue could be either disparity or texture, and was not necessarily the less reliable cue. Optimally weighted averaging has previously been modeled as the combination of Gaussian sensory estimators. We show that both weighted averaging and robustness are predicted if the tails of the sensory estimators are heavier than a Gaussian. Lastly, we probed to see whether access to single-cue estimates determined robustness behavior. We found no evidence for access, suggesting nearly full cue fusion of disparity and texture slant estimates. We used this data to estimate a 'coupling prior' for disparity-texture combination.

Yibin Tian, PhD

Title
Optical Aberrations, Retinal Image Quality and Eye Growth: Experimentation and Modeling

Abstract
Retinal image quality is important for normal eye growth. Optical aberrations are of interest for two reasons: first, they degrade retinal images; second, they might provide some cues to defocus. Higher than normal ocular aberrations have been previously associated with human myopia. However, these studies were cross-sectional in design, and only reported aberrations in terms of root mean square (RMS) errors of Zernike coefficients, a poor metric of optical quality.

This dissertation presents results from investigations of ocular optical aberrations, retinal image quality and eye growth in chicks and humans. A number of techniques were utilized, including Shack-Hartmann aberrometry, high-frequency A-scan ultrasonography, ciliary nerve section (CNX), photorefractive keratectomy (PRK) as well as computer simulations and modeling. A technique to extract light scatter information from Shack-Hartmann images was also developed. The main findings of the dissertation are summarized below.

In young chicks, most ocular aberrations decreased with growth in both normal and CNX eyes, and there were diurnal fluctuations in some aberrations. Modeling suggested active reduction in higher order aberrations (HOAs) during early development. Although CNX eyes manifested greater than normal HOAs, they showed near normal growth.

Retinal image degradation varied greatly among individual eyes post-PRK in young chicks. Including light scatter information into analyses of retinal image quality better estimated the latter. Albino eyes showed more severe retinal image degradation than normal eyes, due to increased optical aberrations and light scatter, but their growth was similar to that of normal eyes, implying that they were relatively insensitive to retina image quality.

Although the above results questioned the influence of optical aberrations on early ocular growth, some optical quality metrics, derived from optical aberrations data, could predict how much the eyes of young chicks subsequently elongated. The performance of some focus measures was very poor when non-defocus aberrations exceeded a certain level; presumably, these non-defocus aberrations might interfere with the eye’s ability to interpret defocus.

In anisomyopic human adults, more myopic eyes had larger anterior and vitreous chambers, greater astigmatism, and more positive spherical aberration. However, compared to isometropes, only interocular differences in spherical equivalent refractive errors were significantly increased.