Deep Convolutional Neural Networks Outperform Feature-Based But Not Categorical Models in Explaining Object Similarity Judgments.

Recent advances in Deep convolutional Neural Networks (DNNs) have enabled unprecedentedly accurate computational models of brain representations, and present an exciting opportunity to model diverse cognitive functions. State-of-the-art DNNs achieve human-level performance on object categorisation, but it is unclear how well they capture human behavior on complex cognitive tasks. Recent reports suggest that DNNs can explain significant variance in one such task, judging object similarity. Here, we extend these findings by replicating them for a rich set of object images, comparing performance across layers within two DNNs of different depths, and examining how the DNNs' performance compares to that of non-computational "conceptual" models. Human observers performed similarity judgments for a set of 92 images of real-world objects. Representations of the same images were obtained in each of the layers of two DNNs of different depths (8-layer AlexNet and 16-layer VGG-16). To create conceptual models, other human observers generated visual-feature labels (e.g., "eye") and category labels (e.g., "animal") for the same image set. Feature labels were divided into parts, colors, textures and contours, while category labels were divided into subordinate, basic, and superordinate categories. We fitted models derived from the features, categories, and from each layer of each DNN to the similarity judgments, using representational similarity analysis to evaluate model performance. In both DNNs, similarity within the last layer explains most of the explainable variance in human similarity judgments. The last layer outperforms almost all feature-based models. Late and mid-level layers outperform some but not all feature-based models. Importantly, categorical models predict similarity judgments significantly better than any DNN layer. Our results provide further evidence for commonalities between DNNs and brain representations. Models derived from visual features other than object parts perform relatively poorly, perhaps because DNNs more comprehensively capture the colors, textures and contours which matter to human object perception. However, categorical models outperform DNNs, suggesting that further work may be needed to bring high-level semantic representations in DNNs closer to those extracted by humans. Modern DNNs explain similarity judgments remarkably well considering they were not trained on this task, and are promising models for many aspects of human cognition

Comparative study of radiation-induced damage in magnesium aluminate spinel by means of IL, CL and RBS/C techniques

International audienceA comparative study of damage accumulation in magnesium aluminate spinel (MgAl2O4) has been conducted using ionoluminescence (IL), cathodoluminescence (CL) and Rutherford Backscattering Spectrometry/channeling (RBS/C) techniques. MgAl2O4 single crystal and polycrystalline samples were irradiated with 320 keV Ar+ ions at fluencies ranging from 1 × 1012 to 2 × 1016 cm−2 in order to create various levels of radiation damage. RBS/C measurements provided quantitative data about damage concentration in the samples. These values were then compared to the luminescence measurements. The results obtained by IL and RBS/C methods demonstrate a two-step character of damage buildup process. The CL data analysis points to the three-step damage accumulation mechanism involving the first defect transformation at fluencies of about 1013 cm−2 and second at about 1015 cm−2. The rate of changes resulting from the formation of nonluminescent recombination centers is clearly nonlinear and cannot be described in terms of continuous accumulation of point defects. Both, IL and CL techniques, appear as new, complementary tools bringing new possibilities in the damage accumulation studies in single- and polycrystalline materials

The Role of Aspirin in Preeclampsia Prevention: State of the Art

Introdução: O papel do ácido acetilsalicílico (AAS ou aspirina) na prevenção das complicações associadas à pré-eclâmpsia tem sido objeto de estudos e de controvérsias ao longo de 30 anos. Os primeiros trabalhos de investigação acerca do papel da placenta na génese da pré-eclâmpsia surgiram em finais dos anos 70 e assinalavam um aumento da atividade plaquetária e alteração da síntese das prostaglandinas, como consequência da deficiente adaptação da placenta. Ao longo dos últimos 20 anos do século XX, sucederam-se estudos de investigação acerca do papel profilático da aspirina na redução do risco de pré-eclâmpsia. Material e Métodos: Para analisar os trabalhos publicados sobre o uso da aspirina na prevenção da pré-eclâmpsia, bem como sobre a dose mais adequada e momento de administração, foram consultados apenas estudos prospetivos, revisões sistemáticas e meta-análises através das seguintes fontes pesquisa (PubMed, Cochrane, Embase). Os artigos citados foram considerados os mais relevantes. Os trabalhos foram divididos em dois grupos: no primeiro foram incluídos os trabalhos em que a aspirina era administrada até às 16 semanas e o segundo, com início de administração por um período mais alargado. Resultados e Discussão: No primeiro grupo, com menor número de casos, mas com início mais precoce de administração do fármaco, até às 16 semanas, concluiu-se que a aspirina poderia ter um papel positivo na redução de risco de gravidade da pré-eclâmpsia; o segundo grupo, com maior número de casos nos estudos, mas com condições menos restritas de entrada e de tempo de início do fármaco, teve resultados mais controversos. As meta-análises destes estudos concluíram que os resultados favoráveis estavam associados às condições de e momento da administração. Conclusão: Não existindo ainda alternativas ou fármacos que lhe possam ser associados, a aspirina em baixas doses (80 a 150 mg/dia) ao deitar, iniciada no 1º trimestre e até às 16 semanas mantém-se um fármaco seguro, que tem contribuído para redução do risco de pré-eclâmpsia precoce, com as consequências que lhe estão associadas

Revisiting oxidative stress and the use of organic selenium in dairy cow nutrition

In commercial animal production productive stress can negatively impact health status and subseqeunt productive and reproductive performance. A great body of evidence demonstrates that as a conseuquence of productive stress an overproduction of free radicals, disturbance of redox balance/signaling, and oxidative stress are observed. There is a range of antioxidants that can be supplied with animal feed which help build and maintain the antioxidant defense system of the body responsible for prevention of the damaging effects of free radicals and the toxic products of their metabolism. Among feed-derived antioxidants, selenium (Se) is shown to have a special place as an essential part of 25 selenoproteins identified in animals. There is a comprehensive body of research in monogastric species that clearly shows that the Se bioavailability within the diet is very much dependent on the form of the element used. Organic Se, in the form of selenomethionine (SeMet), has been reported to be a much more effective Se source when compared with mineral forms, such as sodium selenite or selenate. It has been proposed that one of the main advantages of organic Se in pig and poultry nutrition is the non-specific incorporation of SeMet into general body proteins, thus forming an endogenous Se reserve that can be utilized during periods of stress for additional synthesis of selenoproteins. Responses in ruminant species to supplementary Se tends to be much more variable than those reported in monogastric species, and much of this variability may be a consequence of the different fates of Se forms in the rumen following ingestion. It is likely that the reducing conditions found in the rumen are responsible for the markedly lower assimilation of inorganic forms of Se, thus predisposing selenite-fed animals to potential Se inadequacy that may in turn compromise animal health and production. There is a growing body of evidence that demonstrates that organic Se has a number of benefits, particularly in dairy and beef animals; these include improved selenium and antioxidant status, and better Se transfer via the placenta, colostrum, and milk to the newborn. However, there is a paucity in the data concerning molecular mechanisms of SeMet assimilation, metabolism and selenoprotein synthesis regulation in ruminant animals, and as such further investigation is required

Impaired antibody-mediated protection and defective IgA B cell memory in experimental infection of adults with respiratory syncytial virus

Rationale: Despite relative antigenic stability, respiratory syncytial virus (RSV) re-infects throughout life. After >40 years of research, no effective human vaccine exists and correlates of protection remain poorly defined. Most current vaccine candidates seek to induce high levels of RSV-specific serum neutralizing antibodies, which are associated with reduced RSV-related hospitalization rates in observational studies but may not actually prevent infection. Objectives: Characterize correlates of protection from infection and the generation of RSV-specific humoral memory to promote effective vaccine development. Methods: We inoculated 61 healthy adults with live RSV and studied protection from infection by serum and mucosal antibody. We analyzed RSV-specific peripheral blood plasmablast and memory B cell frequencies and antibody longevity. Measurements and Main Results: Despite moderately high levels of pre-existing serum antibody, 34 (56%) became infected, of whom 23 (68%) developed symptomatic colds. Prior RSV-specific nasal IgA correlated significantly more strongly with protection from PCR-confirmed infection than serum neutralizing antibody. Increases in virus-specific antibody titers were variable and transient in infected subjects, but correlated with plasmablasts that peaked around day 10. During convalescence, only IgG (and no IgA) RSV-specific memory B cells were detectable in peripheral blood. This contrasted with natural influenza infection, where virus-specific IgA memory B cells were readily recovered. Conclusions: This observed specific defect in IgA memory may partly explain RSV's ability to cause recurrent symptomatic infections. If so, vaccines able to induce durable RSV-specific IgA responses may be more protective than those generating systemic antibody alone

Essays in limitations to technology adoption

While new agricultural technologies may lead to substantial yield improvements, the take-up rates in developing countries have frequently been low. There are many possible reasons why a farmer might refrain from adopting a new technology, and literature has pointed to several possible reasons in different settings. A key area for research is to understand what policies could encourage higher adoption rates. This thesis studies the research question by using a case study of fertiliser adoption in cocoa farming in Ghana. Chapter I investigates whether returns to fertiliser in cocoa farming are high and whether farmers' adoption decisions can be explained by comparative advantage. Chapter I uses data from Ghana to measure the returns to fertiliser using a correlated random model and static and dynamic panel models of homogeneous returns to fertiliser. The estimated returns in different models are positive, high and strongly significant statistically. The chapter also presents a correlated random effects model of heterogeneous technology, which allows for farmer-specific comparative advantage. The effect of the comparative advantage is found not to be statistically significant. Chapter II explores the fertiliser investment decisions and risk preferences of Ghanaian cocoa farmers in a framed field experiment. The experimental subjects decided whether to invest in fertiliser, and the fertiliser return depended on a stochastic weather realisation. An inexpensive index insurance scheme with a positive level of basis risk was found to have a minor positive effect on the fertiliser take-up, but this effect was statistically insignificant. An expensive index insurance scheme with no basis risk was found to have a substantial positive effect, and this effect was strongly significant. The experimental findings suggest that farmers are willing to pay for an index insurance if it successfully shields them from income variability. Chapter III investigates the effect of trust and of an ambiguous environment on fertiliser investments under index insurance. These two behavioural factors were studied by means of a framed field experiment conducted with Ghanaian cocoa farmers. The subjects had an option to invest in a package of fertiliser bundled with index insurance with a positive level of basis risk. The returns depended both on the subjects´ investment choices and a stochastic weather realization. The key ingredient of the study was that for different subjects, the nature of the basis risk was framed differently. Substantially fewer subjects adopted fertiliser when possible losses of fertiliser investment were framed as resulting from the insurer´s failure to meet its contract obligations, compared with an alternative in which the losses were framed as resulting from a mismatch between their own weather realizations and those on which the index insurance was based. A large negative effect on fertiliser investments was also found in treatments with either a small or large ambiguity regarding the exact level of basis risk. Both negative treatment effects were strongly significant. This may suggest that technologies with which farmers are relatively more experienced are more likely to be adopted under index insurance schemes. The overall experimental findings provide evidence that trust and ambiguity may be significant factors other than basis risk, limiting the effectiveness of index insurance in promoting agricultural innovation

Eliciting risk preferences in an artefactual field experiment via replication and an alternative approach

This paper investigates risk preferences using an artefactual field experiment conducted with a non-standard subject pool of farmers in Ghana. I introduce an alternative methodology for studying preferences following replication of a seminal risk elicitation procedure by Binswanger (Am J Agric Econ 62(3):395407, 1980). An important feature of both approaches is that they are easy to understand and, hence, are particularly suitable for eliciting preferences among subjects with low levels of formal education. I successfully replicate Binswanger’s study, documenting how his original result of the moderate level of risk aversion for an average farmer can be generalized to a different country. However, using my alternative approach, whereby lotteries are presented in the loss domain, I find that half of my experimental subjects violated expected utility theory. This approach is of relevance to the current literature on studying risk preferences among subjects with poor literacy skills

Impaired antibody-mediated protection and defective IgA B cell memory in experimental infection of adults with respiratory syncytial virus

Rationale: Despite relative antigenic stability, respiratory syncytial virus (RSV) re-infects throughout life. After >40 years of research, no effective human vaccine exists and correlates of protection remain poorly defined. Most current vaccine candidates seek to induce high levels of RSV-specific serum neutralizing antibodies, which are associated with reduced RSV-related hospitalization rates in observational studies but may not actually prevent infection. Objectives: Characterize correlates of protection from infection and the generation of RSV-specific humoral memory to promote effective vaccine development. Methods: We inoculated 61 healthy adults with live RSV and studied protection from infection by serum and mucosal antibody. We analyzed RSV-specific peripheral blood plasmablast and memory B cell frequencies and antibody longevity. Measurements and Main Results: Despite moderately high levels of pre-existing serum antibody, 34 (56%) became infected, of whom 23 (68%) developed symptomatic colds. Prior RSV-specific nasal IgA correlated significantly more strongly with protection from PCR-confirmed infection than serum neutralizing antibody. Increases in virus-specific antibody titers were variable and transient in infected subjects, but correlated with plasmablasts that peaked around day 10. During convalescence, only IgG (and no IgA) RSV-specific memory B cells were detectable in peripheral blood. This contrasted with natural influenza infection, where virus-specific IgA memory B cells were readily recovered. Conclusions: This observed specific defect in IgA memory may partly explain RSV's ability to cause recurrent symptomatic infections. If so, vaccines able to induce durable RSV-specific IgA responses may be more protective than those generating systemic antibody alone

Effects of a Technology-Assisted Reading Comprehension Intervention for English Learners with Learning Disabilities

This study integrated technology tools into a reading comprehension intervention that used explicit instruction to teach strategies (i.e., asking questions, making connections, and coding the text to monitor for meaning) to mixed-ability small groups, which included four English Learners with learning disabilities in a fourth-grade general education classroom. We used a multiple baseline design across participants to evaluate the effects of instruction on strategy application as measured through comprehension rubrics (Keene, 2006) and on comprehension-question answering as measured through researcher-developed literal and inferential comprehension questions. Results showed that participants applied comprehension strategies and improved their percentage accuracy with answering comprehension questions after being introduced to explicit strategy instruction, a mnemonic to facilitate strategy application, web-based tools, and peer collaboration to co-construct meaning from text. Participants perceived the instructional technology tools (i.e., mind-mapping applications, web-linked text, weblogs, and an interactive whiteboard recording application) and reading comprehension strategy instruction as helpful. Implications for future research and practice are discussed