Efficient spiking neural network model of pattern motion selectivity in visual cortex

Simulating large-scale models of biological motion perception is challenging, due to the required memory to store the network structure and the computational power needed to quickly solve the neuronal dynamics. A low-cost yet high-performance approach to simulating large-scale neural network models in real-time is to leverage the parallel processing capability of graphics processing units (GPUs). Based on this approach, we present a two-stage model of visual area MT that we believe to be the first large-scale spiking network to demonstrate pattern direction selectivity. In this model, component-direction- selective (CDS) cells in MT linearly combine inputs from V1 cells that have spatiotemporal receptive fields according to the motion energy model of Simoncelli and Heeger. Pattern-direction-selective (PDS) cells in MT are constructed by pooling over MT CDS cells with a wide range of preferred directions. Responses of our model neurons are comparable to electrophysiological results for grating and plaid stimuli as well as speed tuning. The behavioral response of the network in a motion discrimination task is in agreement with psychophysical data. Moreover, our implementation outperforms a previous implementation of the motion energy model by orders of magnitude in terms of computational speed and memory usage. The full network, which comprises 153,216 neurons and approximately 40 million synapses, processes 20 frames per second of a 40∈×∈40 input video in real-time using a single off-the-shelf GPU. To promote the use of this algorithm among neuroscientists and computer vision researchers, the source code for the simulator, the network, and analysis scripts are publicly available. © 2014 Springer Science+Business Media New York

Decision-making for delivery location and quality of care among slum-dwellers: a qualitative study in Uttar Pradesh, India.

BackgroundIn 2013, the Government of India launched the National Urban Health Mission (NUHM) in order to better address the health needs of urban populations, including the nearly 100 million living in slums. Maternal and neonatal health indicators remain poor in India. The objective of this study is to highlight the experiences of women, their husbands, and mothers-in-law related to maternal health services and delivery experiences.MethodsIn total, we conducted 80 in-depth interviews, including 40 with recent mothers, 20 with their husbands, and 20 with their mothers-in-law. Purposeful sampling was conducted in order to obtain differences across delivery experiences (facility vs. home), followed by their family members.ResultsMajor factors that influence decision-making about where to seek care included household dynamics and joint-decision-making with families, financial barriers, and perceived quality of care. Women perceived that private facilities were higher quality compared to public facilities, but also more expensive. Disrespectful care, bribes in the facility, and payment challenges were common in this population.ConclusionsA number of programmatic and policy recommendations are highlighted from this study. Future endeavors should include a greater focus on health education and public programs, including educating women on how to access programs, who is eligible, and how to obtain public funds. Families need to be educated on their rights and expectations in facilities. Future programs should consider the role of husbands and mothers-in-law in reproductive decision-making and support during deliveries. Triangulating information from multiple sources is important for future research efforts

Activation in Different Regulatory Settings: Insights from Social Assistance in Switzerland

Abstract englisch: When implementing activation policies in social assistance, professional social workers must cope with the different conditions that impair a person’s ability for employment. Ideally, caseworkers have possibilities to develop an individual tailor-made activation strategy for each client based on professional standards. This task is complex as such, but also strongly limited and influenced by the available activation services and benefits. Here caseworkers must cope with the complex multi-level and multi-actor systems involved in the financing and delivery of activation services. And, it is thus also the larger regulatory setting in which caseworkers operate, that influences the possibilities for a coordinated, effective, and efficient service delivery

Effets directs et indirects du fédéralisme sur les politiques en matière d'égalité entre les femmes et les hommes – Perspectives venues de la Suisse

Le présent article examine comment différentes caractéristiques institutionnelles du système fédéral suisse, à savoir la seconde Chambre du Parlement, le veto cantonal dans les décisions démocratiques directes ainsi que le principe d'autonomie cantonale, influencent le développement des politiques en matière d'égalité entre les femmes et les hommes. L'auteur soutient que les règles décisionnelles fédéralistes ne sont que rarement la raison directe de report ou de blocage de propositions de politiques favorisant l'égalité entre les femmes et les hommes. Ce qui pourrait davantage expliquer l'évolution des politiques, ce sont les effets cachés de règles informelles puissantes, autrement dit l'absence de mobilisation autour de certaines revendications politiques puisque ces normes sont profondément intériorisées par les acteurs de la société. Le fédéralisme contribue indirectement au pouvoir caché des institutions informelles dans le sens où l'autonomie cantonale réduit les opportunités de mobilisation forte et commune qui remette en question de telles normes.This article discusses how different institutional features of the Swiss federalist system, i.e. the second chamber in parliament, the cantonal veto in direct democratic decisions as well as the principle of cantonal autonomy influence the development of gender equality policies. It is argued that federalist decision-making rules are only rarely the direct reason for delayed or blocked policy proposals seeking more gender equality. More relevant for explaining policy development are the hidden effects of powerful informal rules, i.e. the non-mobilization of certain political claims because these norms are firmly internalized by societal actors. Federalism indirectly contributes to this hidden power of informal institutions, since cantonal autonomy reduces the opportunities for strong and united mobilization challenging such norms. (published in french - unpublished English version available

Sparse Factors, Streamlined Time-variation, and Twisted Yield Curves

Chapter 1: Factor Augmented VAR Revisited - A Sparse Dynamic Factor Model Approach with Sylvia Kaufmann We combine the factor augmented VAR framework with recently developed estimation and identification procedures for sparse dynamic factor models. Working with a sparse hierarchical prior distribution allows us to discriminate between zero and non-zero factor loadings. The non-zero loadings identify the unobserved factors and provide a meaningful economic interpretation for them. Applying our methodology to US macroeconomic data reveals indeed a high degree of sparsity in the data. We use the estimated FAVAR to study the effect of a monetary policy shock and a shock to the term premium. Factors and specific variables show sensible responses to the identified shocks. Chapter 2: Streamlining Time-varying VAR with a Factor Structure in the Parameters I introduce a factor structure on the parameters of a Bayesian TVP-VAR to reduce the dimension of the model's state space. To further limit the scope of over-fitting the estimation of the factor loadings uses a new generation of shrinkage priors. A Monte Carlo study illustrates the ability of the proposed sampler to well distinguish between time varying and constant parameters. In an application with Swiss data the model proves useful to capture changes in the economy's dynamics due to the lower bound on nominal interest rates. Chapter 3: Shall we Twist? with Sophie Altermatt In recent monetary history, central banks around the world have started to introduce unconventional monetary policy measures, such as extending or restructuring the asset side of their balance sheet. The origin of these monetary policy tools goes back to an intervention by the U.S. Federal Reserve System under the Kennedy administration in 1961 known as Operation Twist. Operation Twist serves as a perfect laboratory to study the effectiveness of such balance sheet policies, because interest rates neither were at their lower bound nor was the economy in a historical turmoil. We assess the actions of the FED and the Treasury under Operation Twist based on balance sheet data and evaluate their success using modern time series techniques. We find that, although being of rather moderate size, the joint policy actions were effective in compressing the long-short spreads of the Treasury bond rates

The Relative Importance of Depth Cues and Semantic Edges for Indoor Mobility Using Simulated Prosthetic Vision in Immersive Virtual Reality

Visual neuroprostheses (bionic eyes) have the potential to treat degenerative eye diseases that often result in low vision or complete blindness. These devices rely on an external camera to capture the visual scene, which is then translated frame-by-frame into an electrical stimulation pattern that is sent to the implant in the eye. To highlight more meaningful information in the scene, recent studies have tested the effectiveness of deep-learning based computer vision techniques, such as depth estimation to highlight nearby obstacles (DepthOnly mode) and semantic edge detection to outline important objects in the scene (EdgesOnly mode). However, nobody has attempted to combine the two, either by presenting them together (EdgesAndDepth) or by giving the user the ability to flexibly switch between them (EdgesOrDepth). Here, we used a neurobiologically inspired model of simulated prosthetic vision (SPV) in an immersive virtual reality (VR) environment to test the relative importance of semantic edges and relative depth cues to support the ability to avoid obstacles and identify objects. We found that participants were significantly better at avoiding obstacles using depth-based cues as opposed to relying on edge information alone, and that roughly half the participants preferred the flexibility to switch between modes (EdgesOrDepth). This study highlights the relative importance of depth cues for SPV mobility and is an important first step towards a visual neuroprosthesis that uses computer vision to improve a user's scene understanding

A model of ganglion axon pathways accounts for percepts elicited by retinal implants.

Degenerative retinal diseases such as retinitis pigmentosa and macular degeneration cause irreversible vision loss in more than 10 million people worldwide. Retinal prostheses, now implanted in over 250 patients worldwide, electrically stimulate surviving cells in order to evoke neuronal responses that are interpreted by the brain as visual percepts ('phosphenes'). However, instead of seeing focal spots of light, current implant users perceive highly distorted phosphenes that vary in shape both across subjects and electrodes. We characterized these distortions by asking users of the Argus retinal prosthesis system (Second Sight Medical Products Inc.) to draw electrically elicited percepts on a touchscreen. Using ophthalmic fundus imaging and computational modeling, we show that elicited percepts can be accurately predicted by the topographic organization of optic nerve fiber bundles in each subject's retina, successfully replicating visual percepts ranging from 'blobs' to oriented 'streaks' and 'wedges' depending on the retinal location of the stimulating electrode. This provides the first evidence that activation of passing axon fibers accounts for the rich repertoire of phosphene shape commonly reported in psychophysical experiments, which can severely distort the quality of the generated visual experience. Overall our findings argue for more detailed modeling of biological detail across neural engineering applications

Towards Immersive Virtual Reality Simulations of Bionic Vision

Bionic vision is a rapidly advancing field aimed at developing visual neuroprostheses ('bionic eyes') to restore useful vision to people who are blind. However, a major outstanding challenge is predicting what people 'see' when they use their devices. The limited field of view of current devices necessitates head movements to scan the scene, which is difficult to simulate on a computer screen. In addition, many computational models of bionic vision lack biological realism. To address these challenges, we propose to embed biologically realistic models of simulated prosthetic vision (SPV) in immersive virtual reality (VR) so that sighted subjects can act as 'virtual patients' in real-world tasks.Comment: 3 pages, 2 figures, to be presented at Augmented Human