21,075 research outputs found
Binocular contrast discrimination needs monocular multiplicative noise.
The effects of signal and noise on contrast discrimination are difficult to separate because of a singularity in the signal-detection-theory model of two-alternative forced-choice contrast discrimination (Katkov, Tsodyks, & Sagi, 2006). In this article, we show that it is possible to eliminate the singularity by combining that model with a binocular combination model to fit monocular, dichoptic, and binocular contrast discrimination. We performed three experiments using identical stimuli to measure the perceived phase, perceived contrast, and contrast discrimination of a cyclopean sine wave. In the absence of a fixation point, we found a binocular advantage in contrast discrimination both at low contrasts (<4%), consistent with previous studies, and at high contrasts (≥34%), which has not been previously reported. However, control experiments showed no binocular advantage at high contrasts in the presence of a fixation point or for observers without accommodation. We evaluated two putative contrast-discrimination mechanisms: a nonlinear contrast transducer and multiplicative noise (MN). A binocular combination model (the DSKL model; Ding, Klein, & Levi, 2013b) was first fitted to both the perceived-phase and the perceived-contrast data sets, then combined with either the nonlinear contrast transducer or the MN mechanism to fit the contrast-discrimination data. We found that the best model combined the DSKL model with early MN. Model simulations showed that, after going through interocular suppression, the uncorrelated noise in the two eyes became anticorrelated, resulting in less binocular noise and therefore a binocular advantage in the discrimination task. Combining a nonlinear contrast transducer or MN with a binocular combination model (DSKL) provides a powerful method for evaluating the two putative contrast-discrimination mechanisms
-symmetries for discrete equations
Following the usual definition of -symmetries of differential
equations, we introduce the analogous concept for difference equations and
apply it to some examples.Comment: 10 page
Lie discrete symmetries of lattice equations
We extend two of the methods previously introduced to find discrete
symmetries of differential equations to the case of difference and
differential-difference equations. As an example of the application of the
methods, we construct the discrete symmetries of the discrete Painlev\'e I
equation and of the Toda lattice equation
Fixing Food Safety: Protecting America's Food Supply From Farm-to-Fork
Provides an overview of the major concerns regarding U.S. food safety, including an ineffective regulatory system, and of food-borne disease threats. Includes lists of recent outbreaks, major causes of food-borne illnesses, and recommended solutions
Pandemic Flu and the Potential for U.S. Economic Recession: A State-by-State Analysis
Considers how a severe health pandemic outbreak could impact the United States economy and delineates the potential financial loss each state could face
Tractrices, Bicycle Tire Tracks, Hatchet Planimeters, and a 100-year-old Conjecture
Geometry of the tracks left by a bicycle is closely related with the
so-called Prytz planimeter and with linear fractional transformations of the
complex plane. We describe these relations, along with the history of the
problem, and give a proof of a conjecture made by Menzin in 1906.Comment: 20 pages, 18 figure
- …