Optimal measurement of visual motion across spatial and temporal scales

Sensory systems use limited resources to mediate the perception of a great variety of objects and events. Here a normative framework is presented for exploring how the problem of efficient allocation of resources can be solved in visual perception. Starting with a basic property of every measurement, captured by Gabor's uncertainty relation about the location and frequency content of signals, prescriptions are developed for optimal allocation of sensors for reliable perception of visual motion. This study reveals that a large-scale characteristic of human vision (the spatiotemporal contrast sensitivity function) is similar to the optimal prescription, and it suggests that some previously puzzling phenomena of visual sensitivity, adaptation, and perceptual organization have simple principled explanations.Comment: 28 pages, 10 figures, 2 appendices; in press in Favorskaya MN and Jain LC (Eds), Computer Vision in Advanced Control Systems using Conventional and Intelligent Paradigms, Intelligent Systems Reference Library, Springer-Verlag, Berli

Light cone effect on the reionization 21-cm signal – II. Evolution, anisotropies and observational implications

Measurements of the H I 21-cm power spectra from the reionization epoch will be influenced by the evolution of the signal along the line-of-sight direction of any observed volume. We use numerical as well as seminumerical simulations of reionization in a cubic volume of 607 Mpc across to study this so-called light-cone effect on the H I 21-cm power spectrum. We find that the light-cone effect has the largest impact at two different stages of reionization: one when reionization is ∼20 per cent and other when it is ∼80 per cent completed. We find a factor of ∼4 amplification of the power spectrum at the largest scale available in our simulations. We do not find any significant anisotropy in the 21-cm power spectrum due to the light-cone effect. We argue that for the power spectrum to become anisotropic, the light-cone effect would have to make the ionized bubbles significantly elongated or compressed along the line of sight, which would require extreme reionization scenarios. We also calculate the two-point correlation functions parallel and perpendicular to the line of sight and find them to differ. Finally, we calculate an optimum frequency bandwidth below which the light-cone effect can be neglected when extracting power spectra from observations. We find that if one is willing to accept a 10 per cent error due to the light-cone effect, the optimum frequency bandwidth for k = 0.056 Mpc−1 is ∼7.5 MHz. For k = 0.15 and 0.41 Mpc−1, the optimum bandwidth is ∼11 and ∼16 MHz, respectively

Compensation for Changing Motor Uncertainty

When movement outcome differs consistently from the intended movement, errors are used to correct subsequent movements (e.g., adaptation to displacing prisms or force fields) by updating an internal model of motor and/or sensory systems. Here, we examine changes to an internal model of the motor system under changes in the variance structure of movement errors lacking an overall bias. We introduced a horizontal visuomotor perturbation to change the statistical distribution of movement errors anisotropically, while monetary gains/losses were awarded based on movement outcomes. We derive predictions for simulated movement planners, each differing in its internal model of the motor system. We find that humans optimally respond to the overall change in error magnitude, but ignore the anisotropy of the error distribution. Through comparison with simulated movement planners, we found that aimpoints corresponded quantitatively to an ideal movement planner that updates a strictly isotropic (circular) internal model of the error distribution. Aimpoints were planned in a manner that ignored the direction-dependence of error magnitudes, despite the continuous availability of unambiguous information regarding the anisotropic distribution of actual motor errors

Optimal Compensation for Temporal Uncertainty in Movement Planning

Motor control requires the generation of a precise temporal sequence of control signals sent to the skeletal musculature. We describe an experiment that, for good performance, requires human subjects to plan movements taking into account uncertainty in their movement duration and the increase in that uncertainty with increasing movement duration. We do this by rewarding movements performed within a specified time window, and penalizing slower movements in some conditions and faster movements in others. Our results indicate that subjects compensated for their natural duration-dependent temporal uncertainty as well as an overall increase in temporal uncertainty that was imposed experimentally. Their compensation for temporal uncertainty, both the natural duration-dependent and imposed overall components, was nearly optimal in the sense of maximizing expected gain in the task. The motor system is able to model its temporal uncertainty and compensate for that uncertainty so as to optimize the consequences of movement

Stability analysis of second order fluid flow models with state-dependent parameters

Theme 1 - Reseaux et systemes - Projet ArmorSIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : 22588, issue : a.2001 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Stability analysis of second order fluid flow models with state-dependent parameters

Theme 1 - Reseaux et systemes - Projet ArmorSIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : 14802 E, issue : a.2001 n.4133 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Late Cardiotoxicity: Issues for Childhood Cancer Survivors

Cardiovascular-related morbidity is a substantial health burden in survivors of childhood cancers. This burden is gaining importance as this population increases through advancements in therapy. Anthracyclines are commonly used agents that are known to cause late cardiotoxicity. Cardiotoxicity is also increased by other risk factors, such as concurrent radio- or chemotherapy, younger age at diagnosis, female sex, comorbidities, lifestyle factors, and genetic factors, such as hemochromatosis gene mutations. Treatment of late cardiotoxicity depends on the type of cardiac abnormalities and consists of pharmacotherapy, mechanical support, or heart transplantation. Because cardiotoxicity is progressive and often irreversible, prevention, risk reduction, and early detection are of utmost importance. The cardioprotectant dexrazoxane decreases anthracycline cardiotoxicity. Screening for other risk factors at the time of diagnosis may identify risk that when present, if used to tailor therapy, may reduce the severity of cardiac damage. The effects of exercise and other lifestyle changes in reducing the cardiovascular diseases in cancer survivors are unclear. However, it may be beneficial to encourage survivors to engage in physical activity tailored to survivor medical status, but with close monitoring