Mirror Symmetry is Subject to Crowding Across the Visual Field

Bilateral mirror symmetry is often thought to be particularly salient to human observers. It has been hypothesized that symmetry engages specialized mechanisms that evolved to sense symmetrical objects in nature. However, although symmetry is a commonly encountered stimulus property, studies have shown that sensitivity to mirror symmetry does not serve an alerting function when embedded in noise (Gurnsey et al., Can Soc Brain Behav Cog Sci, 1998b). Further, sensitivity to symmetry decreases similarly to other common stimuli when targets are presented away from the centre of the visual field (for review: Wagemans, Spat Vis, 1995). The three experiments presented in this thesis show that symmetrical targets are vulnerable to the same interference as other stimuli when surrounded by non-target elements. The data shares many of the common characteristics attributable to the crowding phenomenon in current and historical literature (for review: Whitney & Levi, Trends Cog Sci, 2011). Namely, we find little or no effect of crowding at fixation. The magnitude of the crowding effect increased nonlinearly with eccentricity and at a greater rate than the linear increase of resolution loss (e.g., Gurnsey et al., JoV, 2011; Latham & Whitaker, Ophthalmic Physiol Opt, 1996). In this case, standard double linear size scaling procedures were unable to characterize the data across the visual field and produced untenable results that violate assumptions of the crowding phenomenon. Taken together, the results provide evidence that symmetry is unlikely to be processed in parallel fashion by low-level mechanisms

Confinement without boundaries: Anisotropic diffusion on the surface of a cylinder

Densely packed systems of thermal particles in curved geometries are frequently encountered in biological and microfluidic systems. In 2D systems, at sufficiently high surface coverage, diffusive motion is widely known to be strongly affected by physical confinement, e.g., by the walls. In this Letter, we explore the effects of confinement by shape, not rigid boundaries, on the diffusion of particles by confining them to the surface of a cylinder. We find that both the magnitude and the directionality of lateral diffusion is strongly influenced by the radius of the cylinder. An anisotropy between diffusion in the longitudinal and circumferential direction of the cylinder develops. We demonstrate that the origin of this effect lies in the fact that screw-like packings of mono- and oligodisperse discs on the surface of a cylinder induce preferential collective motions in the circumferential direction, but also show that even in polydisperse systems lacking such order an intrinsic finite size confinement effect increases diffusivity in the circumferential direction

Geometry-dependent critical currents in superconducting nanocircuits

In this paper we calculate the critical currents in thin superconducting strips with sharp right-angle turns, 180-degree turnarounds, and more complicated geometries, where all the line widths are much smaller than the Pearl length $\Lambda = 2 \lambda^2/d$. We define the critical current as the current that reduces the Gibbs free-energy barrier to zero. We show that current crowding, which occurs whenever the current rounds a sharp turn, tends to reduce the critical current, but we also show that when the radius of curvature is less than the coherence length this effect is partially compensated by a radius-of-curvature effect. We propose several patterns with rounded corners to avoid critical-current reduction due to current crowding. These results are relevant to superconducting nanowire single-photon detectors, where they suggest a means of improving the bias conditions and reducing dark counts. These results also have relevance to normal-metal nanocircuits, as these patterns can reduce the electrical resistance, electromigration, and hot spots caused by nonuniform heating.Comment: 29 pages, 24 figure

Useful Government Spending, Direct Crowding Out and Fiscal Policy Interdependence.

This paper introduces perfect substitutability between private and public consumption in a dynamic, open economy with imperfect competition and nominal rigidities. This implies a direct crowding-out effect that, generalizing to the two-country case some well-known properties of a closed economy, tends to reduce consumption following both domestic and foreign expansions. A less expected result is that sub-stitutability has a positive effect on the short-run output spillover.COMPETITION ; PRICES ; FISCAL POLICY

Mirror symmetrical transfer of perceptual learning by prism adaptation

AbstractRecent study of [Sugita, Y. (1996) Global plasticity in adult visual cortex following reversal of visual input. Nature, 380, 523–526.] demonstrated that prism adaptation to reversed retinal input generates the transfer of neuronal activities in monkey V1 to the opposite visual cortex. This raises the question if perceptual learning on one side of the visual field can transfer to the other side. We tested this in using the Gabor lateral masking paradigm. Before adaptation, long-range interaction was induced vertically on one side (i.e., the right) of the visual field with training (perceptual learning). Prism adaptation was achieved by wearing right-left reversing goggles. During adaptation period, perceptual learning transferred to a mirror symmetrical region across the vertical meridian. Results in the post adaptation period revealed that both learning and transfer persisted for over three months. These results provide direct evidence of transferred perceptual plasticity across the visual field, the underlying mechanism of which is supported by the mirror symmetrical connection between the right and left cortices

Peripheral vision and pattern recognition:a review

We summarize the various strands of research on peripheral vision and relate them to theories of form perception. After a historical overview, we describe quantifications of the cortical magnification hypothesis, including an extension of Schwartz's cortical mapping function. The merits of this concept are considered across a wide range of psychophysical tasks, followed by a discussion of its limitations and the need for non-spatial scaling. We also review the eccentricity dependence of other low-level functions including reaction time, temporal resolution, and spatial summation, as well as perimetric methods. A central topic is then the recognition of characters in peripheral vision, both at low and high levels of contrast, and the impact of surrounding contours known as crowding. We demonstrate how Bouma's law, specifying the critical distance for the onset of crowding, can be stated in terms of the retinocortical mapping. The recognition of more complex stimuli, like textures, faces, and scenes, reveals a substantial impact of mid-level vision and cognitive factors. We further consider eccentricity-dependent limitations of learning, both at the level of perceptual learning and pattern category learning. Generic limitations of extrafoveal vision are observed for the latter in categorization tasks involving multiple stimulus classes. Finally, models of peripheral form vision are discussed. We report that peripheral vision is limited with regard to pattern categorization by a distinctly lower representational complexity and processing speed. Taken together, the limitations of cognitive processing in peripheral vision appear to be as significant as those imposed on low-level functions and by way of crowding

Footloose Capital, Market Access, and the Geography of Regional State Aid

The global welfare implications of home market effects in trade models with imperfect competition are little understood. This paper proposes a simple model in which such implications can be easily analyzed. It shows an overall tendency of imperfectly competitive sectors to inefficiently cluster in locations that offer market access advantages. The more so the stronger the market power of firms as well as the intensity of increasing returns to scale and the lower the trade costs. As such features are likely to differ widely across sectors, those results provide theoretical ground to the promotion of regional policies that are also sectorspecific and not only region-specific as currently in the EU.economic integration, specialization, home market effect, regional disparities, regional policy, International Relations/Trade, Political Economy, F12, L13, R13,

Charge transport and mobility engineering in two-dimensional transition metal chalcogenide semiconductors

Two-dimensional (2D) van der Waals semiconductors represent the thinnest, air stable semiconducting materials known. Their unique optical, electronic and mechanical properties hold great potential for harnessing them as key components in novel applications for electronics and optoelectronics. However, the charge transport behavior in 2D semiconductors is more susceptible to external surroundings (e.g. gaseous adsorbates from air and trapped charges in substrates) and their electronic performance is generally lower than corresponding bulk materials due to the fact that surface and bulk coincide. In this article, we review recent progress on the charge transport properties and carrier mobility engineering of 2D transition metal chalcogenides, with a particular focus on the markedly high dependence of carrier mobility on thickness. We unveil the origin of this unique thickness dependence and elaborate the devised strategies to master it for carrier mobility optimization. Specifically, physical and chemical methods towards the optimization of the major factors influencing the extrinsic transport such as electrode/semiconductor contacts, interfacial Coulomb impurities and atomic defects are discussed. In particular, the use of \textit{ad-hoc} molecules makes it possible to engineer the interface with the dielectric and heal the vacancies in such materials. By casting fresh light onto the theoretical and experimental works, we provide a guide for improving the electronic performance of the 2D semiconductors, with the ultimate goal of achieving technologically viable atomically thin (opto)electronics.Comment: 33 pages, 19 figures and 6 table