SEARCH · PubMed Health

Results for “Explainability”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 793 records · Page 44Linked to original sources

PubMed2002

Uniformity and asymmetry of rapid curved-line detection explained by parallel categorical coding of contour curvature.

The aim of this work was to elucidate several characteristic phenomena associated with rapid curved-line detection in multi-element arrays and to provide a unified account of the underlying curvature-sensitive mechanisms. To this end, a parametric experiment was performed in which the detectability of a curved-line target in a briefly presented planar array of curved-line distractors was measured for a range of target and distractor curvatures and distractor numbers. For both vertically oriented and randomly oriented curved lines, it was found that (1) the dependence of target detectability on target curvature was independent of distractor number for small distractor curvatures but not for medium-to-large distractor curvatures; (2) an asymmetry in target detectability with respect to interchange of target and distractor curvatures occurred only with large distractor numbers; and (3) with small distractor numbers, target detectability depended only on the difference between target and distractor curvatures. These properties of spatial parallelism, asymmetry, and uniformity were explained quantitatively by a minimal model of rapid curved-line detection in which contour curvature was coded in terms of just two or three curvature categories, depending on curved-line orientation.

Adult↗

PubMed2003

Effects of contrast and length on vernier acuity explained with noisy templates.

Vernier acuity depends on the integration of information from multiple photoreceptors. For this reason, vernier acuity thresholds ought to exhibit effects of stimulus size and contrast analogous to those that occur in area summation experiments. In this paper, we consider some area and contrast effects found in vernier acuity experiments, and explain them with a model of detection and discrimination which we call the Noisy Template model. The Noisy Template model assumes that psychophysical tasks are performed (or can be approximated) by cross-correlation of the stimulus with a decision template which is optimal for the task at hand. The Noisy Template model crucially adds the assumption that the template contains noise. This yields inefficiency in the decision process which increases with stimulus size and contrast. Predictions of the Noisy Template model are derived for the case of vernier acuity, and compared with existing experiments.

Contrast Sensitivity↗

PubMed2003

Attentional selection of superimposed surfaces cannot be explained by modulation of the gain of color channels.

When two differently colored, superimposed patterns of dots rotate in opposite directions, this yields the percept of two superimposed transparent surfaces. If observers are cued to attend to one set of dots, they are impaired in making judgments about the other set. Since the two sets of dots are overlapping, the cueing effect cannot be explained by spatial attention. This has led to the interpretation that the impairment reflects surface-based attentional selection. However, recent single-unit recording studies in monkeys have found that attention can modulate the gain of neurons tuned for features such as color. Thus, rather than reflecting the selection of a surface, the behavioral effects might simply reflect a reduction in the gain of color channels selective for the color of the uncued set of dots (feature-based attention), as if viewing the surfaces through a colored filter. If so, then the impairment should be eliminated when the two surfaces are made the same color. Instead, we find that the impairment persists with no reduction in strength. Our findings thus rule out the color gain explanation.

Adult↗

PubMed2003

A model using MT-like motion-opponent operators explains an illusory transformation in the optic flow field.

Previous studies have shown that a physiologically based model using motion-opponent operators to compute heading performs accurately for simulated observer translations. Here we show how this model can explain an illusory shift in the perceived focus of expansion of a radial flow field that occurs when a field of laterally moving dots is superimposed on a field of radially moving dots. Furthermore, we can use the model to predict the perceptual shift of the focus of expansion for novel visual stimuli. These results support the hypothesis that this illusion results from motion subtraction during the processing of optic flow fields.

Computer Simulation↗

PubMed1997

Band-limited contrast in natural images explains the detectability of changes in the amplitude spectra.

The psychophysical task of discriminating changes in the slopes of the amplitude spectra of complex images has been used in the past to test whether the human visual system might be optimised for coding the spatial structure in natural images (e.g. Knill et al., 1990; Tadmor & Tolhurst, 1994). We have reported that the dependency of these discrimination thresholds on the reference slope has the same overall general form, regardless of the particular digitised photographs that are used for generating the stimuli. The actual discrimination thresholds, however, differ markedly in magnitude for stimuli that are derived from different digitised photographs. Here, we describe a model that aims at explaining this diversity of threshold magnitudes: we suppose that the observer is detecting small changes in image contrast estimated within limited spatial-frequency bands of about 1 octave bandwidth. This local-contrast analysis reveals that contrast changes in only one frequency band are of comparable magnitudes to the changes that observers need for detecting differences in the Michelson contrast of simple sinusoidal gratings. The success of this band-limited contrast model is further shown in experiments where the slopes of the amplitude spectra of stimuli were changed only within restricted frequency bands. We show that when the slope is changed outside the limited frequency band implicated by the contrast model, the observer's thresholds are greatly elevated. Thresholds remain unchanged when slope changes are made within the implicated band. We also find that the exact bandwidth of the contrast operator is not critical, provided that it is in the range of about 0.6-1.5, which is the characteristic bandwidth range of V1 neurons.

Contrast Sensitivity↗

PubMed1999

A neural model of saccadic eye movement control explains task-specific adaptation.

Multiple brain learning sites are needed to calibrate the accuracy of saccadic eye movements. This is true because saccades can be made reactively to visual cues, attentively to visual or auditory cues, or planned in response to memory cues using visual, parietal, and prefrontal cortex, as well as superior colliculus, cerebellum, and reticular formation. The organization of these sites can be probed by displacing a visual target during a saccade. The resulting adaptation typically shows incomplete and asymmetric transfer between different tasks. A neural model of saccadic system learning is developed to explain these data, as well as data about saccadic coordinate changes.

Adaptation, Physiological↗

PubMedDate not supplied

Potential pathways and exposure to explain the human body burden of organochlorine compounds: a multivariate statistical analysis of human monitoring in Würzburg, Germany.

By means of multivariate statistical analysis of human monitoring in the vicinity of Würzburg it is examined whether the organochlorine levels in blood data of 309 persons can in part be explained by pollution from outdoor and/or indoor air. Although diet is the main source for intake this study concentrated on the remaining sources. Using 12 personal and geographical variables, which describe some aspects or components of indoor or outdoor exposure, the quantities of the different pathways for the intake are calculated and shown. Besides the impact of the indoor air, which can be pointed out for intake at the workplace for some PCB-congeners, also the hypothesis of the existence of an intake from outdoor air for some organochlorine compounds cannot be rejected. Here, the origin is the spatial variation of the pollution, which can be directly traced back to micro-climatic processes, local relief conditions, and the functional set-up of the town.

Air Pollution↗

PubMed1981

The cardiac malformations. Double inlet left ventricle and corrected transposition explained as deviations in the normal development of the interventricular septum.

To examine the hypothesis that malpositions of cardiac ventricles could be explained by altered development of the interventricular septum, we studied hearts from the Johns Hopkins Hospital autopsy files with double inlet left ventricle (16 cases) or corrected transposition (nine cases). In double inlet left ventricle (16 cases) or corrected transposition (nine cases). In double inlet ventricle both atrioventricular valves connect normally developed and positioned right and left atria to a posterior morphologic left ventricle. In hearts with corrected transposition the atria are normally positioned and the morphologic right ventricle is on the left and is continuous with the anteriorly positioned aorta. The morphologic left ventricle is on the right, connected to the posteriorly positioned pulmonary trunk. Normal ventricular septation may be understood as arising from the mechanics of a spiral fold in the primary heart tube produced by the left interventricular sulcus. The ventral limb of the spiral induces the muscular interventricular septum while the dorsal limb becomes a component of the crista supraventricularis. We propose that double inlet left ventricle and corrected transposition are the result of minor deviations in the position of the interventricular sulcus on the primary heart tube. Double inlet left ventricle may develop from the formation of a closed unspiraled ring around the interventricular canal. Corrected transposition may result from a left interventricular sulcus whose ventral limb gives rise to a left sided crista supraventricularis, which determines in part the right ventricular morphology of the left sided ventricle. The dorsal limb spirals toward th atrioventricular canal, gives rise to a malpositioned interventricular septum, and displaces the embryonic trabeculated right ventricle to the left. The concept presented accounts for the morphologic findings characteristic of double inlet left ventricle and corrected transposition.

Adolescent↗

PubMed2001

Replicative mosaicism might explain the seeming contradictions in the telomere theory of aging.

All living organisms are regarded as a mosaic of cells with different replicative histories explaining all the contradictions in the telomere theory of aging. Exhausted proliferative potential of cells in some areas of the organ tissue might be sufficient to promote one of the age-dependent diseases. Thus a combination of these disorders, gradually increasing with age, is aging. Nobody dies because of the age. Nothing other than the age-related diseases occur with age, and if we separate these diseases, we will get not just a healthy old man, but according to Dr Hayflick's new hypothesis (Exp. Gerontol., 33 (1998) 639) a healthy young man, if not a newborn child.

Aging↗

PubMed1999

HSP70 induction may explain the long-lasting resistance to heat of Drosophila melanogaster having lived in hypergravity.

In this study, we showed that in flies kept for 2 weeks at 1 (terrestrial gravity), 3 or 5 x g (hypergravity, HG) before transfer to 1 x g, resistance to heat remained higher in HG flies for several weeks after the transfer. The measurement of heat shock protein 70 (hsp70) indicated no induction of the protein in HG, but the study revealed that flies living in HG expressed more hsp70 only after being submitted to severe stress. The higher induction of hsp70 may explain the higher thermotolerance of these HG-treated young flies. Finally, an unknown protein was observed only in females. This protein may belong to a class of higher molecular weight hsp (hsp110), which have not previously been observed in Drosophila.

Age Factors↗

PubMed2003

Explaining lake and catchment change using sediment derived and written histories: an Australian perspective.

Palaeolimnological records can be powerfully combined with documentary data to explain the impact of modern industry and agriculture on lake systems and their catchments. Such an approach is highly appropriate in Australia since modern society was imposed on a continent until recently populated solely by hunter-gatherers and because there is a wealth of historical data to draw upon. Confounding factors such as the influence of climate change, depopulation of the indigenous community and non-linear responses to human impact must be considered in analysis of the relative importance of various land use changes upon lake pollution.

Agriculture↗

PubMed2000

Do escape mutants explain rapid increases in dengue case-fatality rates within epidemics?

During the Cuban dengue epidemics of 1981 and 1997, significant monthly increases were observed in the proportion of total cases that presented as dengue haemorrhagic fever or dengue shock syndrome (DHF/DSS), and in case-fatality rates for both dengue fever and DHF/DSS. We believe that theses increases can be explained by the hypothesis that some of the population of antibodies against dengue 1 virus raised after natural primary infections react with "neutralisation" determinants found on dengue 2 viruses. These heterotypic antibodies do not prevent secondary dengue 2 infections, but serve to down-regulate the disease to mild illness or symptomless infections. A population of dengue 2 viruses that replicates in dengue-1-immune hosts escape heterotypic neutralisation. When inoculated into a new dengue-1-immune host, these viruses are free to interact with the more abundant infection-enhancing antibodies to produce severe disease.

Antibodies, Viral↗

PubMed2000

Explaining trends in inequities: evidence from Brazilian child health studies.

There is considerable international concern that child-health inequities seem to be getting worse between and within richer and poorer countries. The "inverse equity hypothesis" is proposed to explain how such health inequities may get worse, remain the same, or improve over time. We postulate that as new public-health interventions and programmes initially reach those of higher socioeconomic status and only later affect the poor, there are early increases in inequity ratios for coverage, morbidity, and mortality indicators. Inequities only improve later when the rich have achieved new minimum achievable levels for morbidity and mortality and the poor gain greater access to the interventions. The hypothesis was examined using three epidemiological data sets for time trends in child-health inequities within Brazil. Time trends for inequity ratios for morbidity and mortality, which were consistent with the hypothesis, showed both improvements and deterioration over time, despite the indicators showing absolute improvements in health status between rich and poor.

Brazil↗

PubMed1983

Inadequacy of APUD concept in explaining production of peptide hormones by tumours.

The amine precursor uptake and decarboxylation (APUD) system of cells has been claimed to derive from the embryological neural crest. This assertion has been uncritically accepted. There is much contradictory evidence, especially about the origin of the gastrointestinal and respiratory APUD cells. There is further evidence that the embryological derivation of a particular cell does not relate to the possibility of ectopic peptide hormone synthesis by malignant tumours arising from that cell type. There are many reports of APUD activity by endodermally and mesodermally derived tumours, and of "APUDomas" with endodermal microscopic features. It seems that the concept of dedifferentiation explains the observed data much more satisfactorily and that the presence of double minute chromosomes may denote gene amplification and cellular production of peptides.

APUD Cells↗

PubMed2003

Models in which many cross-bridges attach simultaneously can explain the filament movement per ATP split during muscle contraction.

Contractile filaments in skeletal muscle are moved by less than 2nm for each ATP used. If just one cross-bridge is attached to each thin filament at any instant then this distance represents the fundamental myosin cross-bridge step size (i.e. the distance one cross-bridge moves a thin filament in one ATP-splitting cycle). However, most contraction models assume many cross-bridges are attached at any instant along each thin filament. The purpose of this study was to establish whether the net filament sliding per ATP used could be explained quantitatively in terms of a cross-bridge model in which multiple cross-bridges are attached along each thin filament. It was found that the relationship between net filament sliding per ATP split and the load against which the muscle shortens is compatible with such a model and furthermore predicts that the cross-bridge step size is between 7.5 and 12.5nm over most of the range of loads. These values were similar for different muscle fibre types.

Actin Cytoskeleton↗

PubMed1998

Does a decrease in subplasmalemmal Ca2+ explain how store-operated Ca2+ channels are opened?

The phenomenon of store-activated Ca2+ inflow (capacitative Ca2+ entry) in which the depletion of Ca2+ in the endoplasmic reticulum (ER) increases the probability of opening of store-operated Ca2+ channels (SOCs) located in the plasma membrane is ubiquitous in 'non-excitable' animal cells and is also found in some 'excitable' cells. At present, neither the structures of SOCs nor the mechanism(s) by which a decrease in Ca2+ in the lumen of the ER activates SOCs are well understood. This paper discusses the hypothesis that a decrease in the concentration of Ca2+ in restricted regions of the subplasmalemmal space (bounded by the plasma membrane and peripheral regions of the ER) is responsible for the activation of SOCs. The hypothesis rests on observations made by others that Ca2+ is a strong feed-back inhibitor of SOCs and of the endoplasmic reticulum (Ca(2+)+Mg2+)-ATPases (SERCAs), and on the concepts (developed previously by others) of a subplasmalemmal space and the directed flow of Ca2+ through SOCs into the lumen of the ER and from there to the deep cytoplasmic space. The way in which the hypothesis might explain the actions of agonists (acting via inositol 1,4,5-trisphosphate) and thapsigargin (an inhibitor of SERCAs) in activating SOCs under physiological conditions is described. The proposed involvement of thapsigargin-insensitive SERCAs, and possible limitations of the hypothesis are discussed.

Calcium↗

PubMed1999

A model of multivalent ligand-receptor equilibria which explains the effect of multivalent binding inhibitors.

Quantitative relationships based on multivalent ligand receptor binding equilibria are developed which can describe the enhanced binding observed when polyvalent ligands are used as inhibitors of cell/cell interactions. This theory is able to explain the many orders of magnitude difference reported between the apparent dissociation constants determined for the interaction of Entamoeba histolytica membrane receptors with mono and multivalent N-Acetylgalactosaminide inhibitors. Given two experimentally accessible constants the theory provides a framework for the quantitative evaluation of custom designed polyvalent inhibitors of lectin and antibody mediated interactions.

Animals↗

PubMed2003

Are gender differences in depression explained by gender differences in co-morbid anxiety?

BACKGROUND: This review tested the hypothesis that gender differences in depression rates are a function of gender differences in co-morbid anxiety disorders. METHOD: We identified studies using diagnostic criteria, and reporting rates of pure depression, pure anxiety and co-morbid depression and anxiety, separately for females and males. The results of these studies were examined to assess the level of support for the co-morbidity hypothesis. RESULTS: Although some studies supported or partially supported the hypothesis, the methodologically superior studies did not. CONCLUSIONS: We conclude that women are more likely than men to be diagnosed with either disorder alone or co-morbidly. Furthermore, the ratio of women to men who experience anxiety alone or anxiety in combination with depression tends to be higher than the ratio of women to men who experience depression alone. Attempts to explain the gender difference in rates of depression would benefit from an understanding that women also are more likely to experience anxiety.

Adult↗