Visual efficiency detection index : a new composite measure of visual search

Visual search is an important component of our interaction with our surroundings, allowing us to successfully identify external cues that impact our spatial navigation. Previous research has established fixation duration, fixation count, saccade velocity, and saccade amplitude as important indices of visual search. We examined the Visual Efficiency Detection Index (VEDI) comprising multiple aspects of visual search performance into a single measure of global visual performance. Forty participants, 10 adults ages 22-48, and children ages 6, 8, and 10, completed tests of working memory and visual search in response to stimuli relevant to pedestrian decision making. Results indicated VEDI statistically relates to established indices of visual search in relation to their interpretability for human performance. The VEDI was also sensitive to developmental differences in visual search performance, suggesting insight to its utility in the developmental psychological literature.

Find the difference! : eye tracking study on information seeking behavior using an online game

With the advent of digital era web applications have become inevitable part of our lives. We are using the web to manage even the financially or ethically sensitive issues. For this reason exploration of information seeking behavior is an exciting area of research. Current study provides insight on information seeking behavior using a classic ‘Find the Difference’ game. 50 university students between the age of 19 and 26 participated in the study. Eye movement data were recorded with a Tobii T120 device. Participants carried out 4 continuous tasks. Each task included two pictures side by side with 7 hidden differences. After finishing the tasks, participants were asked to repeat the game with the same picture set. This data collection methodology allows the evaluation of learning curves. Additionally, participants were asked about their hand preference. For the purpose of analysis the following metrics were applied: task times (including saccades), fixation count and fixation duration (without saccades). The right- and left-hand side on each picture was selected as AOI (Area of Interest) to detect side preference in connection with hand preference. Results suggest a significant difference between male and female participants regarding aggregated task times (male 58.37s respectively female 68.37s), deviation in the number of fixations and fixation duration (apparently female have less but longer fixations) and also in the distribution of fixations between AOIs. Using eyetracking data current paper highlights the similarities and differences in information acquisition strategies respectively reveals gender and education (Arts vs. Sciences) dependent characteristics of interaction.

Eye movements of beginning and more skilled readers

The present study aimed to analyze and compare the eye movements of beginning (2nd grade) and more skilled (4th grade) readers, during reading words and pseudo-words aloud, that differ in frequency (just for words), regularity and length. In this way, one intends to analyze the process of visual information extraction, by both groups, and detect experience and practice-related changes in the ocular behavior. The eye movements of 34 children were monitored, while these were reading words/pseudo-words lists, and this was accomplished using eye-tracking technology. The results show statistically significant differences between the two groups, in mean and total fixations duration for high-frequency words, in mean fixation duration for regular words and in the mean saccade amplitude in irregular pseudo-words. However, no significant differences were found between the groups on the study of the other variables. Nevertheless, the results suggest that skilled readers tend to show more effective eye movements, what determined a lesser effect of words’ frequency, regularity and length on this group. Moreover, the pseudo-words processing was more difficult than that of words, in both groups.

Emotion recognition in multiple sclerosis

The effect of multiple sclerosis (MS) on the ability to identify emotional expressions in faces was investigated, and possible associations with patients’ characteristics were explored. 56 non-demented MS patients and 56 healthy subjects (HS) with similar demographic characteristics performed an emotion recognition task (ERT), the Benton Facial Recognition Test (BFRT), and answered the Hospital Anxiety and Depression Scale (HADS). Additionally, MS patients underwent a neurological examination and a comprehensive neuropsychological evaluation. The ERT consisted of 42 pictures of faces (depicting anger, disgust, fear, happiness, sadness, surprise and neutral expressions) from the NimStim set. An iViewX high-speed eye tracker was used to record eye movements during ERT. The fixation times were calculated for two regions of interest (i.e., eyes and rest of the face). No significant differences were found between MS and HC on ERT’s behavioral and oculomotor measures. Bivariate and multiple regression analyses revealed significant associations between ERT’s behavioral performance and demographic, clinical, psychopathological, and cognitive measures.

Biological and chemical assessment of zinc ageing in field soils

As zinc (Zn) is both an essential trace element and potential toxicant, the effects of Zn fixation in soil are of practical significance. Soil samples from four field sites amended with ZnSO4 were used to investigate ageing of soluble Zn under field conditions over a 2-year period. Lability of Zn measured using 65Zn radioisotope dilution showed a significant decrease over time and hence evidence of Zn fixation in three of the four soils. However, 0.01 M CaCl2 extractions and toxicity measurements using a genetically modified lux-marked bacterial biosensor did not indicate a decrease in soluble/bioavailable Zn over time. This was attributed to the strong regulatory effect of abiotic properties such as pH on these latter measurements. These results also showed that Zn ageing occurred immediately after Zn spiking, emphasising the need to incubate freshly spiked soils before ecotoxicity assessments. Ageing effects were detected in Zn-amended field soils using 65Zn isotopic dilution as a measure of lability, but not with either CaCl2 extractions or a lux-marked bacterial biosensor.

Latitude and longitude vertical disparities

The literature on vertical disparity is complicated by the fact that several different definitions of the term “vertical disparity” are in common use, often without a clear statement about which is intended or a widespread appreciation of the properties of the different definitions. Here, we examine two definitions of retinal vertical disparity: elevation-latitude and elevation-longitude disparities. Near the fixation point, these definitions become equivalent, but in general, they have quite different dependences on object distance and binocular eye posture, which have not previously been spelt out. We present analytical approximations for each type of vertical disparity, valid for more general conditions than previous derivations in the literature: we do not restrict ourselves to objects near the fixation point or near the plane of regard, and we allow for non-zero torsion, cyclovergence, and vertical misalignments of the eyes. We use these expressions to derive estimates of the latitude and longitude vertical disparities expected at each point in the visual field, averaged over all natural viewing. Finally, we present analytical expressions showing how binocular eye position—gaze direction, convergence, torsion, cyclovergence, and vertical misalignment—can be derived from the vertical disparity field and its derivatives at the fovea.

Calcium carbonate solubilization through H-proton release from some legumes grown in calcareous saline-sodic soils

Increasing levels of CO2 and H+ proton in the rhizosphere from some legumes may play an important role in calcite dissolution of calcareous salt affected soils. Soils planted with white and brown varieties of cowpea (Vigna unguiculata L.) and hyacinth bean (Dolichos lablab L.) relying on either fertilizer N (KNO3) or N-fixation were compared against soils to which gypsum was applied and a control without plants and gypsum application to study the possibility of Ca2+ release from calcite and Na+ leaching. As compared to plants relying on inorganic N, leachates from all pore volumes (0·5, 1·0, 1·5, 2·0 pore volume) in lysimeters planted with N-fixing hyacinth bean contained significantly higher concentrations of HCO with lower concentrations from lysimeters planted with white cowpea relying on N-fixation. However, the lowest concentrations of HCO were recorded in the gypsum and control treatments. In initial leaching, lysimeters planted with N-fixing plants maintained similar leachate Ca2+ and Na+ concentrations compared to gypsum amended soils. However, gypsum amended soils were found to have a prolonged positive effect on Na+ removal. It might be concluded that some legumes that are known to fix N in calcareous salt affected soils may be an alternative ameliorant to the extremely expensive gypsum through calcite solubilization and a consequent release of Ca2+.

Distribution of selected heavy metals in sediments of the Agueda river (Central Portugal)

The state of river water deterioration in the Agueda hydrographic basin, mostly in the western part, partly reflects the high rate of housing and industrial development in this area in recent years. The streams have acted as a sink for organic and inorganic loads from several origins: domestic and industrial sewage and agricultural waste. The contents of the heavy metals Cr, Cd, Ni, Cu, Pb, and Zn were studied by sequential chemical extraction of the principal geochemical phases of streambed sediments, in the <63 mum fraction, in order to assess their potential availability to the environment, investigating, the metal concentrations, assemblages, and trends. The granulometric and mineralogical characteristics of this sediment fraction were also studied. This study revealed clear pollution by Cr, Cd, Ni, Cu, Zn, and Pb, as a result from both natural and anthropogenic origins. The chemical transport of metals appears to be essentially by the following geochemical phases, in decreasing order of significance: (exchangeable + carbonates) much greater than (organics) much greater than (Mn and Fe oxides and hydroxides). The (exchangeable + carbonate) phase plays an important part in the fixation of Cu, Ni, Zn, and Cd. The organic phase is important in the fixation of Cr, Pb, and also Cu and Ni. Analyzing the metal contents in the residual fraction, we conclude that Zn and Cd are the most mobile, and Cr and Pb are less mobile than Cu and Ni. The proximity of the pollutant sources and the timing of the influx of contaminated material control the distribution of the contaminant-related sediments locally and on the network scale.

Human amygdala responses during presentation of happy and neutral faces: correlations with state anxiety

BACKGROUND: Previous functional imaging studies demonstrating amygdala response to happy facial expressions have all included the presentation of negatively valenced primary comparison expressions within the experimental context. This study assessed amygdala response to happy and neutral facial expressions in an experimental paradigm devoid of primary negatively valenced comparison expressions. METHODS: Sixteen human subjects (eight female) viewed 16-sec blocks of alternating happy and neutral faces interleaved with a baseline fixation condition during two functional magnetic resonance imaging scans. RESULTS: Within the ventral amygdala, a negative correlation between happy versus neutral signal changes and state anxiety was observed. The majority of the variability associated with this effect was explained by a positive relationship between state anxiety and signal change to neutral faces. CONCLUSIONS: Interpretation of amygdala responses to facial expressions of emotion will be influenced by considering the contribution of each constituent condition within a greater subtractive finding, as well as 1) their spatial location within the amygdaloid complex; and 2) the experimental context in which they were observed. Here, an observed relationship between state anxiety and ventral amygdala response to happy versus neutral faces was explained by response to neutral faces.

Gaze fixations predict brain activation during the voluntary regulation of picture-induced negative affect

Recent studies have identified a distributed network of brain regions thought to support cognitive reappraisal processes underlying emotion regulation in response to affective images, including parieto-temporal regions and lateral/medial regions of prefrontal cortex (PFC). A number of these commonly activated regions are also known to underlie visuospatial attention and oculomotor control, which raises the possibility that people use attentional redeployment rather than, or in addition to, reappraisal as a strategy to regulate emotion. We predicted that a significant portion of the observed variance in brain activation during emotion regulation tasks would be associated with differences in how participants visually scan the images while regulating their emotions. We recorded brain activation using fMRI and quantified patterns of gaze fixation while participants increased or decreased their affective response to a set of affective images. fMRI results replicated previous findings on emotion regulation with regulation differences reflected in regions of PFC and the amygdala. In addition, our gaze fixation data revealed that when regulating, individuals changed their gaze patterns relative to a control condition. Furthermore, this variation in gaze fixation accounted for substantial amounts of variance in brain activation. These data point to the importance of controlling for gaze fixation in studies of emotion regulation that use visual stimuli.

Iron Uptake and Homeostasis in Microorganisms

Preface. Iron is considered to be a minor element employed, in a variety of forms, by nearly all living organisms. In some cases, it is utilised in large quantities, for instance for the formation of magnetosomes within magnetotactic bacteria or during use of iron as a respiratory donor or acceptor by iron oxidising or reducing bacteria. However, in most cases the role of iron is restricted to its use as a cofactor or prosthetic group assisting the biological activity of many different types of protein. The key metabolic processes that are dependent on iron as a cofactor are numerous; they include respiration, light harvesting, nitrogen fixation, the Krebs cycle, redox stress resistance, amino acid synthesis and oxygen transport. Indeed, it is clear that Life in its current form would be impossible in the absence of iron. One of the main reasons for the reliance of Life upon this metal is the ability of iron to exist in multiple redox states, in particular the relatively stable ferrous (Fe2+) and ferric (Fe3+) forms. The availability of these stable oxidation states allows iron to engage in redox reactions over a wide range of midpoint potentials, depending on the coordination environment, making it an extremely adaptable mediator of electron exchange processes. Iron is also one of the most common elements within the Earth’s crust (5% abundance) and thus is considered to have been readily available when Life evolved on our early, anaerobic planet. However, as oxygen accumulated (the ‘Great oxidation event’) within the atmosphere some 2.4 billion years ago, and as the oceans became less acidic, the iron within primordial oceans was converted from its soluble reduced form to its weakly-soluble oxidised ferric form, which precipitated (~1.8 billion years ago) to form the ‘banded iron formations’ (BIFs) observed today in Precambrian sedimentary rocks around the world. These BIFs provide a geological record marking a transition point away from the ancient anaerobic world towards modern aerobic Earth. They also indicate a period over which the bio-availability of iron shifted from abundance to limitation, a condition that extends to the modern day. Thus, it is considered likely that the vast majority of extant organisms face the common problem of securing sufficient iron from their environment – a problem that Life on Earth has had to cope with for some 2 billion years. This struggle for iron is exemplified by the competition for this metal amongst co-habiting microorganisms who resort to stealing (pirating) each others iron supplies! The reliance of micro-organisms upon iron can be disadvantageous to them, and to our innate immune system it represents a chink in the microbial armour, offering an opportunity that can be exploited to ward off pathogenic invaders. In order to infect body tissues and cause disease, pathogens must secure all their iron from the host. To fight such infections, the host specifically withdraws available iron through the action of various iron depleting processes (e.g. the release of lactoferrin and lipocalin-2) – this represents an important strategy in our defence against disease. However, pathogens are frequently able to deploy iron acquisition systems that target host iron sources such as transferrin, lactoferrin and hemoproteins, and thus counteract the iron-withdrawal approaches of the host. Inactivation of such host-targeting iron-uptake systems often attenuates the pathogenicity of the invading microbe, illustrating the importance of ‘the battle for iron’ in the infection process. The role of iron sequestration systems in facilitating microbial infections has been a major driving force in research aimed at unravelling the complexities of microbial iron transport processes. But also, the intricacy of such systems offers a challenge that stimulates the curiosity. One such challenge is to understand how balanced levels of free iron within the cytosol are achieved in a way that avoids toxicity whilst providing sufficient levels for metabolic purposes – this is a requirement that all organisms have to meet. Although the systems involved in achieving this balance can be highly variable amongst different microorganisms, the overall strategy is common. On a coarse level, the homeostatic control of cellular iron is maintained through strict control of the uptake, storage and utilisation of available iron, and is co-ordinated by integrated iron-regulatory networks. However, much yet remains to be discovered concerning the fine details of these different iron regulatory processes. As already indicated, perhaps the most difficult task in maintaining iron homeostasis is simply the procurement of sufficient iron from external sources. The importance of this problem is demonstrated by the plethora of distinct iron transporters often found within a single bacterium, each targeting different forms (complex or redox state) of iron or a different environmental condition. Thus, microbes devote considerable cellular resource to securing iron from their surroundings, reflecting how successful acquisition of iron can be crucial in the competition for survival. The aim of this book is provide the reader with an overview of iron transport processes within a range of microorganisms and to provide an indication of how microbial iron levels are controlled. This aim is promoted through the inclusion of expert reviews on several well studied examples that illustrate the current state of play concerning our comprehension of how iron is translocated into the bacterial (or fungal) cell and how iron homeostasis is controlled within microbes. The first two chapters (1-2) consider the general properties of microbial iron-chelating compounds (known as ‘siderophores’), and the mechanisms used by bacteria to acquire haem and utilise it as an iron source. The following twelve chapters (3-14) focus on specific types of microorganism that are of key interest, covering both an array of pathogens for humans, animals and plants (e.g. species of Bordetella, Shigella, , Erwinia, Vibrio, Aeromonas, Francisella, Campylobacter and Staphylococci, and EHEC) as well as a number of prominent non-pathogens (e.g. the rhizobia, E. coli K-12, Bacteroides spp., cyanobacteria, Bacillus spp. and yeasts). The chapters relay the common themes in microbial iron uptake approaches (e.g. the use of siderophores, TonB-dependent transporters, and ABC transport systems), but also highlight many distinctions (such as use of different types iron regulator and the impact of the presence/absence of a cell wall) in the strategies employed. We hope that those both within and outside the field will find this book useful, stimulating and interesting. We intend that it will provide a source for reference that will assist relevant researchers and provide an entry point for those initiating their studies within this subject. Finally, it is important that we acknowledge and thank wholeheartedly the many contributors who have provided the 14 excellent chapters from which this book is composed. Without their considerable efforts, this book, and the understanding that it relays, would not have been possible. Simon C Andrews and Pierre Cornelis

Acclimation of photosynthesis to elevated CO2 in onion (Allium cepa) grown at a range of temperatures

Onion (Allium cepa) was grown in the field within temperature gradient tunnels (providing about -2.5degreesC to +2.5degreesC from outside temperatures) maintained at either 374 or 532 mumol mol(-1) CO2. Plant leaf area was determined non-destructively at 7 day intervals until the time of bulbing in 12 combinations of temperature and CO2 concentration. Gas exchange was measured in each plot at the time of bulbing, and the carbohydrate content of the leaf (source) and bulb (sink) was determined. Maximum rate of leaf area expansion increased with mean temperature. Leaf area duration and maximum rate of leaf area expansion were not significantly affected by CO2. The light-saturated rates of leaf photosynthesis (A(sat)) were greater in plants grown at normal than at elevated CO2 concentrations at the same measurement CO2 concentration. Acclimation of photosynthesis decreased with an increase in growth temperature, and with an increase in leaf nitrogen content at elevated CO2. The ratio of intercellular to atmospheric CO2 (C-i/C-a ratio) was 7.4% less for plants grown at elevated compared with normal CO2. A(sat) in plants grown at elevated CO2 was less than in plants grown at normal CO2 when compared at the same C-i Hence, acclimation of photosynthesis was due both to stomatal acclimation and to limitations to biochemical CO2 fixation. Carbohydrate content of the onion bulbs was greater at elevated than at normal CO2. In contrast, carbohydrate content was less at elevated compared with normal CO2 in the leaf sections in which CO2 exchange was measured at the same developmental stage. Therefore, acclimation of photosynthesis in fully expanded onion leaves was detected despite the absence of localised carbohydrate accumulation in these field-grown crops.

Mutational meltdown in primary endosymbionts: selection limits Muller's ratchet

Background Primary bacterial endosymbionts of insects (p-endosymbionts) are thought to be undergoing the process of Muller's ratchet where they accrue slightly deleterious mutations due to genetic drift in small populations with negligible recombination rates. If this process were to go unchecked over time, theory predicts mutational meltdown and eventual extinction. Although genome degradation is common among p-endosymbionts, we do not observe widespread p-endosymbiont extinction, suggesting that Muller's ratchet may be slowed or even stopped over time. For example, selection may act to slow the effects of Muller's ratchet by removing slightly deleterious mutations before they go to fixation thereby causing a decrease in nucleotide substitutions rates in older p-endosymbiont lineages. Methodology/Principal Findings To determine whether selection is slowing the effects of Muller's ratchet, we determined the age of the Candidatus Riesia/sucking louse assemblage and analyzed the nucleotide substitution rates of several p-endosymbiont lineages that differ in the length of time that they have been associated with their insect hosts. We find that Riesia is the youngest p-endosymbiont known to date, and has been associated with its louse hosts for only 13–25 My. Further, it is the fastest evolving p-endosymbiont with substitution rates of 19–34% per 50 My. When comparing Riesia to other insect p-endosymbionts, we find that nucleotide substitution rates decrease dramatically as the age of endosymbiosis increases. Conclusions/Significance A decrease in nucleotide substitution rates over time suggests that selection may be limiting the effects of Muller's ratchet by removing individuals with the highest mutational loads and decreasing the rate at which new mutations become fixed. This countering effect of selection could slow the overall rate of endosymbiont extinction.

Transcriptomic analysis of rhizobium leguminosarum biovar viciae in symbiosis with host plants pisum sativum and Vicia cracca

Rhizobium leguminosarum bv. viciae forms nitrogen-fixing nodules on several legumes, including pea (Pisum sativum) and vetch (Vicia cracca), and has been widely used as a model to study nodule biochemistry. To understand the complex biochemical and developmental changes undergone by R. leguminosarum bv. viciae during bacteroid development, microarray experiments were first performed with cultured bacteria grown on a variety of carbon substrates (glucose, pyruvate, succinate, inositol, acetate, and acetoacetate) and then compared to bacteroids. Bacteroid metabolism is essentially that of dicarboxylate-grown cells (i.e., induction of dicarboxylate transport, gluconeogenesis and alanine synthesis, and repression of sugar utilization). The decarboxylating arm of the tricarboxylic acid cycle is highly induced, as is gamma-aminobutyrate metabolism, particularly in bacteroids from early (7-day) nodules. To investigate bacteroid development, gene expression in bacteroids was analyzed at 7, 15, and 21 days postinoculation of peas. This revealed that bacterial rRNA isolated from pea, but not vetch, is extensively processed in mature bacteroids. In early development (7 days), there were large changes in the expression of regulators, exported and cell surface molecules, multidrug exporters, and heat and cold shock proteins. fix genes were induced early but continued to increase in mature bacteroids, while nif genes were induced strongly in older bacteroids. Mutation of 37 genes that were strongly upregulated in mature bacteroids revealed that none were essential for nitrogen fixation. However, screening of 3,072 mini-Tn5 mutants on peas revealed previously uncharacterized genes essential for nitrogen fixation. These encoded a potential magnesium transporter, an AAA domain protein, and proteins involved in cytochrome synthesis.

Legumes regulate Rhizobium bacteroid development and persistence by the supply of branched-chain amino acids

One of the largest contributions to biologically available nitrogen comes from the reduction of N-2 to ammonia by rhizobia in symbiosis with legumes. Plants supply dicarboxylic acids as a carbon source to bacteroids, and in return they receive ammonia. However, metabolic exchange must be more complex, because effective N-2 fixation by Rhizobium leguminosarum bv viciae bacteroids requires either one of two broad-specificity amino acid ABC transporters (Aap and Bra). It was proposed that amino acids cycle between plant and bacteroids, but the model was unconstrained because of the broad solute specificity of Aap and Bra. Here, we constrain the specificity of Bra and ectopically express heterologous transporters to demonstrate that branched-chain amino acid (LIV) transport is essential for effective N-2 fixation. This dependence of bacteroids on the plant for LIV is not due to their known down-regulation of glutamate synthesis, because ectopic expression of glutamate dehydrogenase did not rescue effective N-2 fixation. Instead, the effect is specific to LIV and is accompanied by a major reduction in transcription and activity of LIV biosynthetic enzymes. Bacteroids become symbiotic auxotrophs for LIV and depend on the plant for their supply. Bacteroids with aap bra null mutations are reduced in number, smaller, and have a lower DNA content than wild type. Plants control LIV supply to bacteroids, regulating their development and persistence. This makes it a critical control point for regulation of symbiosis. MICROBIOLOGY