Are There Multiple Visual Short-Term Memory Stores?

Background

Classic work on visual short-term memory (VSTM) suggests that people store a limited amount of items for subsequent report. However, when human observers are cued to shift attention to one item in VSTM during retention, it seems as if there is a much larger representation, which keeps additional items in a more fragile VSTM store. Thus far, it is not clear whether the capacity of this fragile VSTM store indeed exceeds the traditional capacity limits of VSTM. The current experiments address this issue and explore the capacity, stability, and duration of fragile VSTM representations.

Methodology/Principal Findings

We presented cues in a change-detection task either just after off-set of the memory array (iconic-cue), 1,000 ms after off-set of the memory array (retro-cue) or after on-set of the probe array (post-cue). We observed three stages in visual information processing 1) iconic memory with unlimited capacity, 2) a four seconds lasting fragile VSTM store with a capacity that is at least a factor of two higher than 3) the robust and capacity-limited form of VSTM. Iconic memory seemed to depend on the strength of the positive after-image resulting from the memory display and was virtually absent under conditions of isoluminance or when intervening light masks were presented. This suggests that iconic memory is driven by prolonged retinal activation beyond stimulus duration. Fragile VSTM representations were not affected by light masks, but were completely overwritten by irrelevant pattern masks that spatially overlapped the memory array.

Conclusions/Significance

We find that immediately after a stimulus has disappeared from view, subjects can still access information from iconic memory because they can see an after-image of the display. After that period, human observers can still access a substantial, but somewhat more limited amount of information from a high-capacity, but fragile VSTM that is overwritten when new items are presented to the eyes. What is left after that is the traditional VSTM store, with a limit of about four objects. We conclude that human observers store more sustained representations than is evident from standard change detection tasks and that these representations can be accessed at will.     

Assessing factors influencing communities’ acceptability of mass drug administration for the elimination of lymphatic filariasis in Guyana

BackgroundGuyana is one of four countries in the Latin American Region where lymphatic filariasis (LF) remains endemic. In preparation for the introduction of a new triple drug therapy regimen (ivermectin, diethylcarbamazine, and albendazole (IDA)) in 2019, an acceptability study was embedded within sentinel site mapping in four regions to assess mass drug administration (MDA) coverage and compliance, acceptability, and perceptions about treatment and disease. The results from this survey would inform the rollout of IDA in Guyana in 2019.MethodsData collection for the study occurred in August 2019, using a validated questionnaire administered by trained enumerators. Across all regions, a total of 1,248 participants were sampled by the Filarial Mapping team. Four-hundred and fifty-one participants aged over 18 years were randomly selected for participation in an expanded acceptability questionnaire. All data were captured in Secure Data Kit (SDK).ResultsAcceptability was measured using a mean acceptability score. Unadjusted mean scores ranged from 24.6 to 29.3, with 22.5 as the threshold of acceptability. Regional variation occurred across many indicators of interest: self-rated understanding about LF, mechanisms of LF transmission, LF drug safety and history of treatment during MDA. Region IV (Georgetown) recorded higher knowledge about LF, but lower compliance and acceptability. Number of pills was not perceived as a concern.ConclusionAcceptability of MDA was good across all four regions under study. Results from this study set a baseline level for key indicators and acceptability, from which the acceptability of IDA can be measured. Regional variations across indicators suggest that localized approaches should be considered for social mobilization and MDA delivery to capture these contextual differences.     

Relationship of nitrate supply with growth rate, plasma membrane-bound and cytosolic nitrate reductase, and tissue nitrate content in tobacco plants

cNR, cytosolic nitrate reductase
PM-NR, plasma membrane-bound nitrate reductase

Activities of plasma membrane-bound nitrate reductase (PM-NR) and cytosolic nitrate reductase (cNR) in tobacco (Nicotiana tabacum L. cv. Samsun) are regulated differently, depending upon the nitrate supply to the culture medium (in sand culture). The cNR activity of roots was higher at low nitrate concentrations with the maximum at 5 mM nitrate supply and declined to low values beyond 5 mM . In contrast, the PM-NR activity of roots increased with higher nitrate concentrations with the maximum at 25 mM nitrate and clearly decreased only at 40 mM . This high PM-NR activity correlated with a low growth rate and might be one of the responses to excess nitrate. Internal nitrate and total nitrogen content of the tissues, however, showed a relative minimum in shoots and in roots of between 15 and 25 mM external nitrate. With declining PM-NR activities beyond 25 mM external nitrate, the nitrate content in the tissue increased indicating an inverse relationship between tissue nitrate content and root PM-NR activity. In leaves both NR activities (cNR and PM-NR) correlated with the internal nitrate content, but with a different response at low nitrate.     

Studies on the formation of lactate and pyruvate from glucose in cultured skin fibroblasts: implications for detection of respiratory chain defects

We investigated the time course of the formation of lactate and pyruvate from glucose in cultured skin fibroblasts from controls, from a patient with a cytochrome c oxidase deficiency and from controls treated with inhibitors of the individual respiratory chain complexes. Fibroblasts from the patient and inhibitor treated fibroblasts produced more lactate and less pyruvate; this resulted in a significant increase in the lactate to pyruvate ratio, reflecting an increased cytosolic NADH/NAD+ redox state. We conclude that measurement of lactate and pyruvate production from glucose in cultured skin fibroblasts can be of value in the diagnosis of inherited diseases of the mitochondrial respiratory chain.     

Specific localization of scallop gill epithelial calmodulin in cilia

Calmodulin has been isolated and characterized from the gill of the bay scallop aequipecten irradians. Quantitative electrophoretic analysis of epithelial cell fractions show most of the calmodulin to be localized in the cilia, specifically in the detergent- solubilized membrane-matrix fraction. Calmodulin represents 2.2 +/- 0.3 percent of the membrane-matrix protein or 0.41 +/- 0.5 percent of the total ciliary protein. Its concentration is at least 10(-4) M if distributed uniformly within the matrix. Extraction in the presence of calcium suggests that the calmodulin is not bound to the axoneme proper. The ciliary protein is identified as a calmodulin on the basis of its calcium- dependent binding to a fluphenazine-sepharose affinity column and its comigration with bovine brain calmodulin on alkaline-urea and SDS polyacrylamide gels in both the presence and absence of calcium. Scallop ciliary calmodulin activates bovine brain phosphodiesterase to the same extent as bovine brain and chicken gizzard calmodulins. Containing trimethyllysine and lacking cysteine and tryptophan, the amino acid composition of gill calmodulin is typical of known calmodulins, except that it is relatively high in serine and low in methionine. Its composition is less acidic than other calmodulins, in agreement with an observed isoelectric point approximately 0.2 units higher than that of bovine brain. Comparative tryptic peptide mapping of scallop gill ciliary and bovine brain calmodulins indicates coincidence of over 75 percent of the major peptides, but at least two major peptides in each show no near-equivalency. Preliminary results using ATP-reactivated gill cell models show no effect of calcium at micromolar levels on ciliary beat or directionality of the lateral cilia, the cilia which constitute the vast majority of those isolated. However, ciliary arrest will occur at calcium levels more than 150 muM. Because calmodulin usually functions in the micromolar range, its role in this system is unclear. Scallop gill ciliary calmodulin may be involved in the direct regulation of dyneintubule sliding, or it may serve some coupled calcium transport function. At the concentration in which it is found, it must also at least act as a calcium buffer.     

Isolation of IIIGlc of the phosphoenolpyruvate-dependent glucose phosphotransferase system of Salmonella typhimurium.

We report a procedure for the isolation of IIIglc of Salmonella typhimurium, a protein component of the phosphoenolpyruvate-dependent sugar phosphotransferase system. IIIGlc is a soluble protein with a molecular weight of 21,000, as determined by gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purified protein is involved in the phosphoenolpyruvate-dependent phosphorylation of methyl alpha-glucoside in vitro. Its affinity for octyl-Sepharose may be an indication of the partial hydrophobic nature of IIIGlc. A specific antiserum against purified IIIGlc was prepared. Growth on different carbon sources did not affect the synthesis of IIIGlc, as determined by quantitative immunoelectrophoresis. Mutations which lower the adenosine 3',5'-phosphate level, such as cya and pts, do not alter the IIIGlc level. The closely related enteric bacteria Escherichia coli and Klebsiella aerogenes contain a protein factor which is closely related to IIIGlc of S. typhimurium, whereas Staphylococcus aureus does not.     

Oxidative phosphorylation in human muscle in patients with ocular myopathy and after general anaesthesia

The fuel preference of human muscle mitochondria has been given. Substrates which are oxidized with low velocity cannot be used to detect defects in oxidative phosphorylation. After general anaesthesia, the oxygen uptake with the different substrates is much lower than after local analgesia. The latter was therefore used in the subsequent study. In 15 out of 18 patients with ocular myopathy, defects in oxidative phosphorylation could be detected in isolated muscle mitochondria prepared from freshly biopsied tissue. Measurement of the activity of segments of the respiratory chain in homogenate from frozen muscle showed no, or minor defects. In two of these patients showing exercise intolerance, decreased oxidation of NAD(+)-linked substrates and apparently normal mitochondrial DNA, further study revealed deficiency of pyruvate dehydrogenase in a girl with ptosis and a high Km of complex I for NADH in a man. Both patients responded to vitamin therapy.     

The use of antibodies to intermediate filament proteins in the differential diagnosis of lymphoma versus metastatic carcinoma

Summary Forty-nine cases encompassing 16 different types of malignant lymphoma were examined for their intermediate filament protein (IFP) type by indirect immunofluorescence microscopy of cryostat sections. In all cases, vimentin was shown to be the only IFP type detectable in these tumours. Lymphomas are negative for keratin and desmin, which are characteristic for benign and malignant epithelial or muscular tissues respectively. In addition, eighteen cases are described in which antibodies to intermediate filament proteins were used successfully to distinguish between lymphoma and metastatic carcinoma where differential diagnosis was difficult or impossible on the basis of routine histology.     

Classification of videocapsule endoscopy image patterns: comparative analysis between patients with celiac disease and normal individuals

Background  

Quantitative disease markers were developed to assess videocapsule images acquired from celiac disease patients with villous atrophy, and from control patients.