Stochastic models of evidence accumulation in changing environments

Organisms and ecological groups accumulate evidence to make decisions. Classic experiments and theoretical studies have explored this process when the correct choice is fixed during each trial. However, we live in a constantly changing world. What effect does such impermanence have on classical results about decision making? To address this question we use sequential analysis to derive a tractable model of evidence accumulation when the correct option changes in time. Our analysis shows that ideal observers discount prior evidence at a rate determined by the volatility of the environment, and the dynamics of evidence accumulation is governed by the information gained over an average environmental epoch. A plausible neural implementation of an optimal observer in a changing environment shows that, in contrast to previous models, neural populations representing alternate choices are coupled through excitation. Our work builds a bridge between statistical decision making in volatile environments and stochastic nonlinear dynamics.Comment: 26 pages, 7 figure

Evidence accumulation and change rate inference in dynamic environments

In a constantly changing world, animals must account for environmental volatility when making decisions. To appropriately discount older, irrelevant information, they need to learn the rate at which the environment changes. We develop an ideal observer model capable of inferring the present state of the environment along with its rate of change. Key to this computation is an update of the posterior probability of all possible changepoint counts. This computation can be challenging, as the number of possibilities grows rapidly with time. However, we show how the computations can be simplified in the continuum limit by a moment closure approximation. The resulting low-dimensional system can be used to infer the environmental state and change rate with accuracy comparable to the ideal observer. The approximate computations can be performed by a neural network model via a rate-correlation based plasticity rule. We thus show how optimal observers accumulate evidence in changing environments, and map this computation to reduced models which perform inference using plausible neural mechanisms.Comment: 43 pages, 8 figures, in pres

La metodología b-learning y el aprendizaje del cálculo

El presente trabajo muestra los resultados logrados mediante la utilización del Aula Virtual que ofrece la institución en plataforma Claroline, en el proceso de enseñanza aprendizaje del Cálculo durante 2009 y 2010 en primer año universitario. Se ofreció a los alumnos una metodología de enseñanza con modalidad “blended learning”, que combina clases presenciales con actividades on-line. Se planificaron dichas actividades contando con herramientas de contenido (material de estudio y trabajo), de comunicación (correo electrónico, foro, chat, anuncios y consejos) y de evaluación (cuestionarios, autoevaluativos, actividades) que permitieron un seguimiento del proceso

Molecular and ampelographic characterization of genotypes used for Pajarete wine, an old Denomination of Origin from Huasco and Elqui Valleys in northern Chile

The characterization of 30 grape accessions used to produce Pajarete wine is presented, one of the first American "Denomination of Origin" (D.O.). Accessions were collected from small vineyards from the Huasco Valley in the Atacama Region, northern Chile, which are very heterogeneous for varietal assortment, as was demonstrated by microsatellite marker analysis. Eighteen different genotypes were identified, including the two varieties considered the founders of American viticulture, 'Listán Prieto' (syn. 'País') and 'Muscat of Alexandria'. A series of criolla varieties was also identified, some of them already described plus others not yet included in international databases. Based on nine SSR markers, allelic matchings suggest that four of these new criolla varieties (NN-311, NN-313, NN-368 and NN-370) derives from 'Listán Prieto' x 'Muscat of Alexandria', but three (NN-314, NN-276 and NN-369) are derived from 'M. of Alexandria' crossed with a yet undetermined parent. Seven criolla accessions were described by ampelography, including some not yet recorded in the European Vitis International Variety Catalogue (VIVC) or in the Instituto de Investigaciones Agropecuarias (INIA) database. Three accessions were considered as not appropriate for the production of Pajarete wine since two of them are table grape varieties and the other is the American variety 'Isabella' (Vitis labrusca x V. vinifera), all considered of poor quality for winemaking. All these findings are very useful to direct the conservation of this unique germplasm, as well as for small producers of Pajarete wine, since based on this information on the overall variety assortment of the area, they can now make informed decisions to improve their vineyard management and wine production

Atención de salud después de un terremoto

The earthquake originated in April 2016 in the town of Pedernales, province of Manabí, Ecuador, affected the functioning of health units, health programs of the public system and deteriorated the health of the population. In this study analyzes the effects of the Pedernales earthquake, through the description of the care received by users, in the health units of the MSP in the canton Chone, in the post-earthquake period. An observational, descriptive and cross-sectional study was conducted. The perceptions of the users were studied, determining their degree of satisfaction with the health services received in the health units. The results show that in most of the health units studied there are significant percentages of dissatisfaction in care, there are gaps in access to medicines, hospital beds and health personnel. The earthquake showed the shortcomings of the attention of the public health network, which were already present before and that the earthquake aggravated them.El terremoto originado en abril 2016 en la localidad de Pedernales, provincia de Manabí, Ecuador, afectó el funcionamiento de las unidades de salud, los programas sanitarios del sistema público y deterioró la salud de la población. En este estudio se analizan los efectos del terremoto de Pedernales, mediante la descripción de la atención recibida por los usuarios, en las unidades de salud del MSP en el cantón Chone, en el periodo post terremoto mediato. Se realizó estudio observacional, descriptivo y transversal. Se estudiaron las percepciones de los usuarios, determinando su grado de satisfacción con los servicios de salud recibidos en las unidades de salud. Los resultados demuestran que en la mayoría de las unidades de salud estudiadas hay porcentajes importantes de insatisfacción en la atención, existen brechas en el acceso a medicamentos, camas hospitalarias y de personal de salud. El terremoto evidenció las falencias de la atención de la red pública de salud, que ya estaban presentes antes y que el terremoto las agravó

Dialysate Potassium and Mortality in a Prospective Hemodialysis Cohort.

BackgroundStudies examining the association of dialysate potassium concentration and mortality in hemodialysis patients show conflicting findings. We hypothesized that low dialysate potassium concentrations are associated with higher mortality, particularly in patients with high pre-dialysis serum potassium concentrations.MethodsWe evaluated 624 hemodialysis patients from the prospective Malnutrition, Diet, and Racial Disparities in Kidney Disease study recruited from 16 outpatient dialysis facilities over 2011-2015 who underwent protocolized collection of dialysis treatment characteristics every 6 months. We examined the association of dialysate potassium concentration, categorized as 1, 2, and 3 mEq/L, with all-cause mortality risk in the -overall cohort, and stratified by pre-dialysis serum potassium (< 5 vs. ≥5 mEq/L) using case-mix adjusted Cox models.ResultsIn baseline analyses, dialysate potassium concentrations of 1 mEq/L were associated with higher mortality, whereas concentrations of 3 mEq/L were associated with similar mortality in the overall cohort (reference: 2 mEq/L): adjusted hazard ratios (aHRs; 95% CI) 1.70 (1.01-2.88) and 0.95 (0.64-1.39), respectively. In analyses stratified by serum potassium, baseline dialysate potassium concentrations of 1 mEq/L were associated with higher mortality in patients with serum potassium ≥5 mEq/L but not in those with serum potassium < 5 mEq/L: aHRs (95% CI) 2.87 (1.51-5.46) and 0.74 (0.27-2.07), respectively (p interaction = 0.04). These findings were robust with incremental adjustment for serum potassium, potassium-binding resins, and potassium-modifying medications.ConclusionLow (1 mEq/L) dialysate potassium -concentrations were associated with higher mortality, particularly in hemodialysis patients with high pre-dialysis serum potassium. Further studies are needed to identify therapeutic strategies that mitigate inter-dialytic serum potassium accumulation and subsequent high dialysate serum potassium gradients in this population

Manifestations faded gradually replacement of alfalfa ("Medicado sativa L.") by barley ("Hordeum vulgare L.") sprount in portions of Guinea pigs ("Cavia porcellus L.") in the stage of growth

El experimento fue conducido en el Centro de Producción de Cuyes de la Universidad Nacional de Huancavelica con el objetivo de evaluar la utilización de cuatro niveles (0, 25, 50 y 75%) de cebada hidropónica (CH) en substitución de la alfalfa en la alimentación de cuyes machos y hembras de la Línea Perú, en la fase de crecimiento, en número de 72, con 18 días de edad y 175 g de PV inicial medio confinados durante 42 días. Las raciones experimentales isoproteícas, fueron ofrecidos a los animales a voluntad y divididos en dos porciones (8 y 17 h). Fue utilizado el diseño experimental completamente aleatorizado y los tratamientos distribuidos en esquema factorial 2x4 (sexo x niveles de cebada hidropónica) con tres repeticiones por tratamiento, constituido cada unidad experimental por tres cuyes. Existió reducción lineal para machos en el consumo de MS en g/día y g/kg0.75 con el aumento de los niveles de substitución, este comportamiento también fue verificado para el consumo de PC (g/día). Hubo efecto cúbico para el consumo de PC por los cuyes hembras, en g/día, en g/kg0.75 y en %PV. La substitución de la alfalfa por la CH afectó la conversión alimenticia, cuyo comportamiento fue cuadrático y cúbico para machos y hembras, respectivamente. La CH influyó de forma cúbica sobre el peso final y ganancia de peso diario en los cuyes machos y hembras. Se concluye que es posible substituir la alfalfa por la CH hasta el nivel de 75% en cuyes hembras. El nivel de 25% de substitución proporciona las mejores ganancias de peso y pesos finales en cuyes machos y hembras en crecimiento, lo que pone de manifiesto el efecto positivo de la inclusión de la CH en la ración de cuyes en crecimiento.The experiment was conducted at the Center for Guinea Pig Production, National University of Huancavelica in order to evaluate the use of four levels (0, 25, 50 and 75%) of hydroponic barley (CH) in substitution of alfalfa in the feeding male and female guinea pigs of Peru line, in the growth phase, in number of 72, with 18 days of age and 175 g of initial PV means confined for 42 days. Isoproteic the experimental diets were offered ad libitum to the animals and divided in to two portions (8 and 17 h). It was used the completely randomized design and treatments distributed in factorial scheme 2x4 (sex x levels hydroponic barley) with three replicates per treatment, each experimental unit consists of three guinea pigs. Linear reduction existed for males MS consumption in g / g / day kg 0.75 with increasing substitution levels, this behavior was also verified for PC consumption (g / day). There was a cubic effect for consumption by the female guinea pigs PC in g / day, in g / kg0.75 and in % PV. The substitution of CH alfalfa affected by feed conversion, whose behavior was quadratic and cubic for males and females, respectively. The CH influenced cubical on final weight and daily weight gain in male and female guinea pigs. We conclude that it is possible to replace the CH alfalfa to the level of 75% in female guinea pigs. The level of 25% substitution provides the best weight gain and final weights in males and females growing guinea pigs, which shows the positive effect of the inclusion of CH in the ration of growing guinea pigs