Learning the Optimal Control of Coordinated Eye and Head Movements

Various optimality principles have been proposed to explain the characteristics of coordinated eye and head movements during visual orienting behavior. At the same time, researchers have suggested several neural models to underly the generation of saccades, but these do not include online learning as a mechanism of optimization. Here, we suggest an open-loop neural controller with a local adaptation mechanism that minimizes a proposed cost function. Simulations show that the characteristics of coordinated eye and head movements generated by this model match the experimental data in many aspects, including the relationship between amplitude, duration and peak velocity in head-restrained and the relative contribution of eye and head to the total gaze shift in head-free conditions. Our model is a first step towards bringing together an optimality principle and an incremental local learning mechanism into a unified control scheme for coordinated eye and head movements

Fake Superpotential for Large and Small Extremal Black Holes

We consider the fist order, gradient-flow, description of the scalar fields coupled to spherically symmetric, asymptotically flat black holes in extended supergravities. Using the identification of the fake superpotential with Hamilton's characteristic function we clarify some of its general properties, showing in particular (besides reviewing the issue of its duality invariance) that W has the properties of a Liapunov's function, which implies that its extrema (associated with the horizon of extremal black holes) are asymptotically stable equilibrium points of the corresponding first order dynamical system (in the sense of Liapunov). Moreover, we show that the fake superpotential W has, along the entire radial flow, the same flat directions which exist at the attractor point. This allows to study properties of the ADM mass also for small black holes where in fact W has no critical points at finite distance in moduli space. In particular the W function for small non-BPS black holes can always be computed analytically, unlike for the large black-hole case.Comment: 30 pages, LaTeX source. Discussion on the radial evolution of the scalar fields, in relation to the symmetries of the W-function, extended. Table 1 added. Typos correcte

Solar fusion cross sections. II. The pp chain and CNO cycles

We summarize and critically evaluate the available data on nuclear fusion cross sections important to energy generation in the Sun and other hydrogen-burning stars and to solar neutrino production. Recommended values and uncertainties are provided for key cross sections, and a recommended spectrum is given for 8B solar neutrinos. We also discuss opportunities for further increasing the precision of key rates, including new facilities, new experimental techniques, and improvements in theory. This review, which summarizes the conclusions of a workshop held at the Institute for Nuclear Theory, Seattle, in January 2009, is intended as a 10-year update and supplement to Reviews of Modern Physics 70 (1998) 1265.Comment: 54 pages, 20 figures, version to be published in Reviews of Modern Physics; various typos corrected and several updates mad

Activation of superior colliculi in humans during visual exploration

<p>Abstract</p> <p>Background</p> <p>Visual, oculomotor, and – recently – cognitive functions of the superior colliculi (SC) have been documented in detail in non-human primates in the past. Evidence for corresponding functions of the SC in humans is still rare. We examined activity changes in the human tectum and the lateral geniculate nuclei (LGN) in a visual search task using functional magnetic resonance imaging (fMRI) and anatomically defined regions of interest (ROI). Healthy subjects conducted a free visual search task and two voluntary eye movement tasks with and without irrelevant visual distracters. Blood oxygen level dependent (BOLD) signals in the SC were compared to activity in the inferior colliculi (IC) and LGN.</p> <p>Results</p> <p>Neural activity increased during free exploration only in the SC in comparison to both control tasks. Saccade frequency did not exert a significant effect on BOLD signal changes. No corresponding differences between experimental tasks were found in the IC or the LGN. However, while the IC revealed no signal increase from the baseline, BOLD signal changes at the LGN were consistently positive in all experimental conditions.</p> <p>Conclusion</p> <p>Our data demonstrate the involvement of the SC in a visual search task. In contrast to the results of previous studies, signal changes could not be seen to be driven by either visual stimulation or oculomotor control on their own. Further, we can exclude the influence of any nearby neural structures (e.g. pulvinar, tegmentum) or of typical artefacts at the brainstem on the observed signal changes at the SC. Corresponding to findings in non-human primates, our data support a dependency of SC activity on functions beyond oculomotor control and visual processing.</p

Spin-2 spectrum of defect theories

We study spin-2 excitations in the background of the recently-discovered type-IIB solutions of D'Hoker et al. These are holographically-dual to defect conformal field theories, and they are also of interest in the context of the Karch-Randall proposal for a string-theory embedding of localized gravity. We first generalize an argument by Csaki et al to show that for any solution with four-dimensional anti-de Sitter, Poincare or de Sitter invariance the spin-2 excitations obey the massless scalar wave equation in ten dimensions. For the interface solutions at hand this reduces to a Laplace-Beltrami equation on a Riemann surface with disk topology, and in the simplest case of the supersymmetric Janus solution it further reduces to an ordinary differential equation known as Heun's equation. We solve this equation numerically, and exhibit the spectrum as a function of the dilaton-jump parameter $\Delta\phi$. In the limit of large $\Delta\phi$ a nearly-flat linear-dilaton dimension grows large, and the Janus geometry becomes effectively five-dimensional. We also discuss the difficulties of localizing four-dimensional gravity in the more general backgrounds with NS5-brane or D5-brane charge, which will be analyzed in detail in a companion paper.Comment: 41 pages, 6 figure

Testing foundations of quantum mechanics with photons

The foundational ideas of quantum mechanics continue to give rise to counterintuitive theories and physical effects that are in conflict with a classical description of Nature. Experiments with light at the single photon level have historically been at the forefront of tests of fundamental quantum theory and new developments in photonics engineering continue to enable new experiments. Here we review recent photonic experiments to test two foundational themes in quantum mechanics: wave-particle duality, central to recent complementarity and delayed-choice experiments; and Bell nonlocality where recent theoretical and technological advances have allowed all controversial loopholes to be separately addressed in different photonics experiments.Comment: 10 pages, 5 figures, published as a Nature Physics Insight review articl

Determinants of subject visit participation in a prospective cohort study of HTLV infection

<p>Abstract</p> <p>Background</p> <p>Understanding participation in a prospective study is crucial to maintaining and improving retention rates. In 1990–92, following attempted blood donation at five blood centers, we enrolled 155 HTLV-I, 387 HTLV-II and 799 HTLV seronegative persons in a long-term prospective cohort.</p> <p>Methods</p> <p>Health questionnaires and physical exams were administered at enrollment and 2-year intervals through 2004. To examine factors influencing attendance at study visits of the cohort participants we calculated odds ratios (ORs) with generalized estimated equations (GEE) to analyze fixed and time-varying predictors of study visit participation.</p> <p>Results</p> <p>There were significant independent associations between better visit attendance and female gender (OR = 1.31), graduate education (OR = 1.86) and income > $75,000 (OR = 2.68). Participants at two centers (OR = 0.47, 0.67) and of Black race/ethnicity (OR = 0.61) were less likely to continue. Higher subject reimbursement for interview was associated with better visit attendance (OR = 1.84 for$25 vs. $10). None of the health related variables (HTLV status, perceived health status and referral to specialty diagnostic exam for potential adverse health outcomes) significantly affected participation after controlling for demographic variables.</p> <p>Conclusion</p> <p>Increasing and maintaining participation by minority and lower socioeconomic status participants is an ongoing challenge in the study of chronic disease outcomes. Future studies should include methods to evaluate attrition and retention, in addition to primary study outcomes, including qualitative analysis of reasons for participation or withdrawal.</p

The influence of parents and the home environment on preschoolers' physical activity behaviours: A qualitative investigation of childcare providers' perspectives

<p>Abstract</p> <p>Background</p> <p>Physical activity offers numerous physiological and psychological benefits for young children; however, many preschool-aged children are not engaging in sufficient activity. The home environment, inclusive of parent role modeling, has been identified as influencing preschoolers' physical activity. This study sought to examine childcare providers' perspectives of the importance of parents and the home environment for supporting the physical activity behaviours of preschool-aged children (aged 2.5-5 years) attending childcare.</p> <p>Methods</p> <p>A heterogeneous sample of childcare providers (<it>n </it>= 84; response rate 39%) working at childcare facilities in London, Ontario participated. Thirteen semi-structured focus groups were conducted in London centres between February 2009 and February 2010. Focus groups were audio recorded and transcribed verbatim and inductive content analysis was used to code and classify themes. A number of strategies were used to verify the trustworthiness of the data.</p> <p>Results</p> <p>Childcare providers acknowledged their reliance on parents/guardians to create a home environment that complements the positive physical activity messaging children may receive in childcare. Moreover, childcare staff highlighted the need for positive parent role modeling and parent support to encourage active healthy lifestyles among young children.</p> <p>Conclusion</p> <p>This study's findings highlight the need for increased parent-caregiver partnering in terms of communication and cooperation in service of promoting appropriate amounts of physical activity among London preschoolers.</p

Duty, desire or indifference? A qualitative study of patient decisions about recruitment to an epilepsy treatment trial

BACKGROUND: Epilepsy is a common neurological condition, in which drugs are the mainstay of treatment and drugs trials are commonplace. Understanding why patients might or might not opt to participate in epilepsy drug trials is therefore of some importance, particularly at a time of rapid drug development and testing; and the findings may also have wider applicability. This study examined the role of patient perceptions in the decision-making process about recruitment to an RCT (the SANAD Trial) that compared different antiepileptic drug treatments for the management of new-onset seizures and epilepsy. METHODS: In-depth interviews with 23 patients recruited from four study centres. All interviews were tape-recorded and transcribed; the transcripts were analysed thematically using a qualitative data analysis package. RESULTS: Of the nineteen informants who agreed to participate in SANAD, none agreed for purely altruistic reasons. The four informants who declined all did so for very specific reasons of self-interest. Informants' perceptions of the nature of the trial, of the drugs subject to trial, and of their own involvement were all highly influential in their decision-making. Informants either perceived the trial as potentially beneficial or unlikely to be harmful, and so agreed to participate; or as potentially harmful or unlikely to be beneficial and so declined to participate. CONCLUSION: Most patients applied 'weak altruism', while maintaining self-interest. An emphasis on the safety and equivalence of treatments allowed some patients to be indifferent to the question of involvement. There was evidence that some participants were subject to 'therapeutic misconceptions'. The findings highlight the individual nature of trials but nonetheless raise some generic issues in relation to their design and conduct