Eye movement correlates of figure-ground segregation and border-ownership

Oculomotor system controls human eye movements while scanning a scene. One cue used by visual system to make sense of a scene is the border of objects. Our goal is to understand whether oculomotor system has any pre-set predictions while mapping out a scene. To test this hypothesis, we designed a set of 3D scenes by using an integrated 3D projection and eye-tracking system to compare human eye movement patterns during depth cue consistent occlusion (CCO) and inconsistent occlusion (CIO) of a moving target in a pursuit task. In CCO, the moving target gets occluded by an object in front of it or will remain visible if the object is behind. However, in CIO, the moving target gets occluded by an object behind it or will remain visible if the object is in front. It has been known that when a moving target becomes invisible midway on its path, eye pursuit switches to saccades. In this study, we found that least switches to saccades occur in CCO and when the pursuit target is visible. On the other hand, the maximum switches to saccades occur during CIO when the pursuit target is invisible. Saccadic interruption increases slightly in CIO where the target is visible, and even more so in CCO when the target is invisible. We conclude that during scanning a visual scene, human oculomotor system utilizes a set of predictions, perhaps based on accumulated previous experiences, such as "when a moving target goes behind an occluder it should disappear", and when the predictions are challenged, the oculomotor system switches pursuit to saccade. Finally, we present a set of metrics to quantify the interactions between visual-system-based scene segmentation and eye movement patterns, and the interactions between border-ownership and eye movement vectors to establish eye movement correlates of figure-ground segregation and border-ownership.Published versio

Perception of rigidity in three- and four-dimensional spaces

First author draf

Depth propagation across an illusory surface

We investigate the spatiotemporal dynamics of depth filling in on an illusory surface by measuring the temporal asynchrony of perceived depth between an illusory neon-colored surface and real contours. We temporally modulated the horizontal disparity at vertical edges of the illusory surface and measured the perceptual delay for the interpolated surface's depth under two different boundary conditions: disparity given at both sides, or disparity given at one side and a free boundary at the other side. The results showed that the amount of the delay depends on the spatial distance between the measured point and the edges where disparity was physically given. Importantly, the observed delay as a function of spatial distance was clearly different under the two boundary conditions. We found that this difference can be fairly well explained by a model based on a diffusion equation under different boundary conditions. These results support the existence of locally represented depth information and an interpolation process based on mutual interaction of this information

Perception of rigidity in three- and four-dimensional spaces

Our brain employs mechanisms to adapt to changing visual conditions. In addition to natural changes in our physiology and those in the environment, our brain is also capable of adapting to “unnatural” changes, such as inverted visual-inputs generated by inverting prisms. In this study, we examined the brain’s capability to adapt to hyperspaces. We generated four spatial-dimensional stimuli in virtual reality and tested the ability to distinguish between rigid and non-rigid motion. We found that observers are able to differentiate rigid and non-rigid motion of hypercubes (4D) with a performance comparable to that obtained using cubes (3D). Moreover, observers’ performance improved when they were provided with more immersive 3D experience but remained robust against increasing shape variations. At this juncture, we characterize our findings as “3 1/2 D perception” since, while we show the ability to extract and use 4D information, we do not have yet evidence of a complete phenomenal 4D experience

Estrogen Prevents Bone Loss via Estrogen Receptor α and Induction of Fas Ligand in Osteoclasts

SummaryEstrogen prevents osteoporotic bone loss by attenuating bone resorption; however, the molecular basis for this is unknown. Here, we report a critical role for the osteoclastic estrogen receptor α (ERα) in mediating estrogen-dependent bone maintenance in female mice. We selectively ablated ERα in differentiated osteoclasts (ERαΔOc/ΔOc) and found that ERαΔOc/ΔOc females, but not males, exhibited trabecular bone loss, similar to the osteoporotic bone phenotype in postmenopausal women. Further, we show that estrogen induced apoptosis and upregulation of Fas ligand (FasL) expression in osteoclasts of the trabecular bones of WT but not ERαΔOc/ΔOc mice. The expression of ERα was also required for the induction of apoptosis by tamoxifen and estrogen in cultured osteoclasts. Our results support a model in which estrogen regulates the life span of mature osteoclasts via the induction of the Fas/FasL system, thereby providing an explanation for the osteoprotective function of estrogen as well as SERMs