1,304 research outputs found
A First- and Second-Order Motion Energy Analysis of Peripheral Motion Illusions Leads to Further Evidence of “Feature Blur” in Peripheral Vision
No full textAnatomical and physiological differences between the central and peripheral visual systems are well documented. Recent findings have suggested that vision in the periphery is not just a scaled version of foveal vision, but rather is relatively poor at representing spatial and temporal phase and other visual features. Shapiro, Lu, Huang, Knight, and Ennis (2010) have recently examined a motion stimulus (the “curveball illusion”) in which the shift from foveal to peripheral viewing results in a dramatic spatial/temporal discontinuity. Here, we apply a similar analysis to a range of other spatial/temporal configurations that create perceptual conflict between foveal and peripheral vision.To elucidate how the differences between foveal and peripheral vision affect super-threshold vision, we created a series of complex visual displays that contain opposing sources of motion information. The displays (referred to as the peripheral escalator illusion, peripheral acceleration and deceleration illusions, rotating reversals illusion, and disappearing squares illusion) create dramatically different perceptions when viewed foveally versus peripherally. We compute the first-order and second-order directional motion energy available in the displays using a three-dimensional Fourier analysis in the (x, y, t) space. The peripheral escalator, acceleration and deceleration illusions and rotating reversals illusion all show a similar trend: in the fovea, the first-order motion energy and second-order motion energy can be perceptually separated from each other; in the periphery, the perception seems to correspond to a combination of the multiple sources of motion information. The disappearing squares illusion shows that the ability to assemble the features of Kanisza squares becomes slower in the periphery.The results lead us to hypothesize “feature blur” in the periphery (i.e., the peripheral visual system combines features that the foveal visual system can separate). Feature blur is of general importance because humans are frequently bringing the information in the periphery to the fovea and vice versa
The separation of monocular and binocular contrast
No full textThe contrast asynchrony is a stimulus configuration that illustrates the visual system's separable responses to luminance and luminance contrast information (Shapiro, 2008; Shapiro et al., 2004). When two disks, whose luminances modulate in phase with each other, are each surrounded by a disk, one light and one dark, observers can see both the in-phase brightness signals and the antiphase contrast signals and can separate the two. Here we present the results of experiments in which observers viewed a similar stimulus dichoptically. We report that no asynchrony is perceived when one eye is presented with modulating disks and the other eye is presented with the black and white surround rings, nor is an asynchrony perceived in gradient versions of the contrast asynchrony. We also explore the "window shade illusion" (Shapiro, Charles, & Shear-Heyman, 2005) dichoptically and find that when a modulating disk is presented to one eye and a horizontally split black/white annulus is presented to the other, observers perceive a "shading" motion up and down the disk. This shading can be seen in either direction in the binocular condition, but it is almost always seen as moving towards low contrast in the monocular condition. These findings indicate the presence of separable retinal and cortical networks for contrast processing at different temporal and spatial scales
Turbulence Modeling for Oscillatory Pipe Flow
No full textOscillating pipe flows, with zero mean velocity, are common in engineering systems and particularly in Stirling-based engines and heat pumps, e.g. pulse-tube cryogenic coolers. These flows are particularly challenging to model because their flow state depends on both the Reynolds number and the dimensionless frequency or Womerlsey number. A central challenge in modeling these systems is that the Reynolds number varies greatly within the cycle, often crossing from laminar to turbulent flow regimes. Indeed, flows that have super-critical Reynolds numbers may pass between states a total of four times; two laminar-turbulent transitions and two turbulent-laminar transitions. Contrary to a steady flow in which the transition between the laminar and the turbulent regimes is affected only by the Reynolds number, for oscillating flow the transition is affected by a combination of Reos and a dimensionless frequency-based number such as Womersley (Wo). The objective of this work is to develop and validate a computational method that solves the incompressible oscillating flow equations for different combinations of Reos and Wo
Perpetual diamond, the: contrast reversals along thing edges create the appearance of motion in objects
No full textThe breathing light illusion: Illusory size and brightness variation induced by motion
No full textThis chapter discusses the Breathing Light Illusion. The Breathing Light Illusion is a size and brightness illusion elicited by the self-motion of the observer. The stimulus consists of a circular white spot that is presented on a black background, characterized by blurred boundaries. The blurred spot, which in static view seems to glow and exhibits a self-luminance appearance, is perceived as wider, brighter, and more diffuse when it is approached but smaller, darker, and sharper when one recedes from it. A possible explanation of the phenomenon is related to the superimposition of the afterimage on the physical stimulus during dynamical viewing
The separation of monocular and binocular contrast
No full textAbstractThe contrast asynchrony is a stimulus configuration that illustrates the visual system’s separable responses to luminance and luminance contrast information (Shapiro, 2008; Shapiro et al., 2004). When two disks, whose luminances modulate in phase with each other, are each surrounded by a disk, one light and one dark, observers can see both the in-phase brightness signals and the antiphase contrast signals and can separate the two. Here we present the results of experiments in which observers viewed a similar stimulus dichoptically. We report that no asynchrony is perceived when one eye is presented with modulating disks and the other eye is presented with the black and white surround rings, nor is an asynchrony perceived in gradient versions of the contrast asynchrony. We also explore the “window shade illusion” (Shapiro, Charles, & Shear-Heyman, 2005) dichoptically and find that when a modulating disk is presented to one eye and a horizontally split black/white annulus is presented to the other, observers perceive a “shading” motion up and down the disk. This shading can be seen in either direction in the binocular condition, but it is almost always seen as moving towards low contrast in the monocular condition. These findings indicate the presence of separable retinal and cortical networks for contrast processing at different temporal and spatial scales
Spatial filtering, color constancy, and the color-changing dress
No full textThe color-changing dress is a 2015 Internet phenomenon in which the colors in a picture of a dress are reported as blue-black by some observers and white-gold by others. The standard explanation is that observers make different inferences about the lighting (is the dress in shadow or bright yellow light?); based on these inferences, observers make a best guess about the reflectance of the dress. The assumption underlying this explanation is that reflectance is the key to color constancy because reflectance alone remains invariant under changes in lighting conditions. Here, we demonstrate an alternative type of invariance across illumination conditions: An object that appears to vary in color under blue, white, or yellow illumination does not change color in the high spatial frequency region. A first approximation to color constancy can therefore be accomplished by a high-pass filter that retains enough low spatial frequency content so as to not to completely desaturate the object. We demonstrate the implications of this idea on the Rubik’s cube illusion; on a shirt placed under white, yellow, and blue illuminants; and on spatially filtered images of the dress. We hypothesize that observer perceptions of the dress’s color vary because of individual differences in how the visual system extracts high and low spatial frequency color content from the environment, and we demonstrate cross-group differences in average sensitivity to low spatial frequency patterns
Second-order logic : ontological and epistemological problems
No full textIn this thesis I provide a survey over different approaches to second-order logic
and its interpretation, and introduce a novel approach. Of special interest are the
questions whether (a particular form of) second-order logic can count as logic in some
(further to be specified) proper sense of logic, and what epistemic status it occupies.
More specifically, second-order logic is sometimes taken to be mathematical, a mere
notational variant of some fragment of set theory. If this is the case, it might be
argued that it does not have the "epistemic innocence" which would be needed
for, e.g., foundational programmes in (the philosophy of) mathematics for which
second-order logic is sometimes used. I suggest a Deductivist conception of logic,
that characterises logical consequence by means of inference rules, and argue that
on this conception second-order logic should count as logic in the proper sense
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