Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Feature selection”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 1,441 records · Page 80Linked to original sources
PubMedDate not supplied

Channeling of red and green cone inputs to the zebrafish optomotor response.

Visual systems break scenes down into individual features, processed in distinct channels, and then selectively recombine those features according to the demands of particular behavioral tasks. In primates, for example, there are distinct pathways for motion and form processing. While form vision utilizes color information, motion pathways receive input from only a subset of cone photoreceptors and are generally colorblind. To explore the link between early channeling of visual information and behavioral output across vertebrate species, we measured the chromatic inputs to the optomotor response of larval zebrafish. Using cone-isolating gratings, we found that there is a strong input from both red and green cones but not short-wavelength cones, which nevertheless do contribute to another behavior, phototaxis. Using a motion-nulling method, we measured precisely the input strength of gratings that stimulated cones in combination. The fish do not respond to gratings that stimulate different cone types out of phase, but have an enhanced response when the cones are stimulated together. This shows that red and green cone signals are pooled at a stage before motion detection. Since the two cone inputs are combined into a single 'luminance' channel, the response to sinusoidal gratings is colorblind. However, we also find that the relative contributions of the two cones at isoluminance varies with spatial frequency. Therefore, natural stimuli, which contain a mixture of spatial frequencies, are likely to be visible regardless of their chromatic composition.

Animals↗
PubMed1990

Kikuchi-Fujimoto disease mimicking malignant lymphoma.

Histiocytic necrotizing lymphadenitis is a rare, benign entity described independently both by Kikuchi and Fujimoto et al. This disease, which has a broad morphologic spectrum, can readily be mistaken for malignant lymphoma. Our report on the morphologic features in 10 selected cases of this disease highlights those features that mimicked lymphoma and those that helped us to make an accurate diagnosis. The distinctive features were (a) pathologic areas, which are pale and do not occupy the entire lymph node; (b) preserved sinuses in the uninvolved areas; (c) prominent mottling by histiocytes or transformed lymphoid cells in the nonpathologic areas; (d) frequent absence of overt necrosis; (e) presence of benign histiocytes with moderate to marked nuclear irregularities and scanty to moderate cytoplasm that resembled cleaved cells; (f) variable amounts of nuclear debris, usually extracellular; (g) presence of so-called plasmacytoid T cells at the periphery of or immediately outside the pathologic areas; (h) moderate numbers of mitotic figures and transformed lymphoid cells of medium and large size (immunoblasts); and (i) absence of inflammatory and granulomatous reaction. Because overt necrosis is often absent and histiocytes resemble cleaved cells, we support the suggestion that this entity should be called "Kikuchi-Fujimoto disease" rather than "histiocytic necrotizing lymphadenitis."

Adolescent↗
PubMed1994

Neural correlates of attentive selection for color or luminance in extrastriate area V4.

Rhesus monkeys were trained on a conditional orientation discrimination task in order to assess whether attentive selection for a color or luminance stimulus feature would affect visual processing in extrastriate area V4. The task required monkeys to select a bar stimulus based on its color or luminance and then to discriminate the angular tilt of the selected stimulus. The majority of neurons (74%) were selectively activated when the color or luminance of the stimulus in the receptive field matched the color or luminance of the cue. The activity was attenuated when there was not a match between the stimulus and the cue. The differential activation was based on the presence or absence of the stimulus feature and was independent of spatial location. Across the population of V4 neurons, optimal stimuli that matched the selected color or luminance elicited about twice the activity as stimuli that did not match the selected feature. The feature-selective changes in activity were observed to develop beginning about 200 msec after the stimulus onset and were maintained over the remainder of the behavioral trial. In this task the activity of V4 neurons reflected a selection based on the cued feature and not simply the physical color or luminance of the receptive field stimulus. Under these conditions, the topographic representation of the neural activity in area V4 highlights the potential targets in the visual scene at the expense of background objects. These observations offer a physiological counterpart to psychophysical studies suggesting that stimuli can be preferentially selected in parallel across the visual field on the basis of a unique color or luminance feature.

Analysis of Variance↗
PubMed2000

Optimizing parameters for computer-aided diagnosis of microcalcifications at mammography.

RATIONALE AND OBJECTIVES: The purpose of this study was to optimize selection of the mammographic features most useful in discriminating benign from malignant clustered microcalcifications. MATERIALS AND METHODS: The computer-aided diagnosis (CAD) system automatically extracted from digitized mammograms 13 quantitative features characterizing microcalcification clusters. Archival cases (n = 134; patient age range, 31-77 years; mean age, 56.8 years) with known histopathologic results (79 malignant, 55 benign) were selected. Three radiologists at three facilities independently analyzed the microcalcifications by using the CAD system. Stepwise discriminant analysis selected the features best discriminating benign from malignant microcalcifications. A classification scheme was constructed on the basis of these optimized features, and its performance was evaluated by using receiver operating characteristic (ROC) analysis. RESULTS: Six of the 13 variables extracted by the CAD system were selected by stepwise determinant analysis for generating the classification scheme, which yielded an ROC curve with an area (Az) of 0.98, specificity of 83.64%, positive predictive value of 89.53%, and accuracy of 91.79% for 98% sensitivity. When patient age was an additional variable, the scheme's performance improved, but this was not statistically significant (Az = 0.98). The ROC curve of the classifier (without age as an additional variable) yielded a high Az of 0.96 for patients younger than 50 years and an even higher (P < .02) Az of 0.99 for those 50 years or older. CONCLUSION: Stepwise discriminant analysis optimized performance of a classification scheme for microcalcifications by selecting six optimized features. Scheme performance was significantly (P < .02) higher for women 50 years or older, but the addition of patient age as a variable did not produce a statistically significant increase in performance.

Adult↗
PubMed2002

Possible pathogenic mechanisms in inflammatory myopathies.

The limitations associated with the different approaches into the pathogenesis of the IIM have resulted in incomplete knowledge of disease mechanisms in myositis. In most research, in which muscle tissue was used to study the different aspects of disease, biopsies with inflammatory infiltrates have been selected. Although inflammatory cell infiltrates are a characteristic feature of myositis, selecting patients with inflammatory cell infiltrates for investigations naturally introduces a selection bias. Only a few studies have been published on patients without inflammatory infiltrates but with muscle weakness, and few studies have included follow-up biopsies after different therapies. The heterogeneity of the population of patients with myositis is another limitation of the studies of pathogenic mechanisms. Although most studies classify patients according to the Bohan and Peter criteria [118, 119], some studies used histopathologic criteria [6], and only a few studies included characterization with myositis-specific autoantibodies. Because myositis-specific autoantibodies are often associated with certain clinical profiles, classification according to autoantibody profiles could be important to define differences in the pathogenesis of different phenotypes [3]. From available data on pathogenic mechanisms it is evident that cellular and humoral immune responses are involved in disease mechanisms of myositis, but whether there is a muscle-specific immune response cannot be answered by current studies. It is likely that other mechanisms are important for development of muscle weakness, including metabolic disturbances, and muscle weakness could be caused by different mechanisms in different IIM subsets or in patients in different phases of the disease. There could be early changes, which reversibly affect the metabolism, and later, irreversible changes, that could be dependent on muscle fiber damage and replacement of muscle tissue by connective tissue and fat. Current findings suggest that cytokines, which are produced in muscle tissue from different cell sources including inflammatory cells, endothelial cells, and muscle fibers, could affect muscle function. Careful follow-up studies, including the effect of therapies targeting different molecules on molecular expression in muscle tissue, are likely to increase our knowledge on disease mechanisms. A better understanding of which molecules and mechanisms affect muscle function is likely to lead to improved, less toxic therapies in patients with myositis. Many possible target molecules for blocking therapies, especially the proinflammatory cytokines IL-1 and TNF-alpha, have been identified and should be studied in appropriate clinical settings given the currently poor outcomes of many patients with IIM.

Autoimmunity↗
PubMed1998

Nucleotide sequence diversity at the alcohol dehydrogenase 1 locus in wild barley (Hordeum vulgare ssp. spontaneum): an evaluation of the background selection hypothesis.

The background selection hypothesis predicts a reduction in nucleotide site diversity and an excess of rare variants, owing to linkage associations with deleterious alleles. This effect is expected to be amplified in species that are predominantly self-fertilizing. To examine the predictions of the background selection hypothesis in self-fertilizing species, we sequenced 1,362 bp of adh1, a gene for alcohol dehydrogenase (Adh; alcohol:NAD+ oxidoreductase, EC 1.1.1.1), in a sample of 45 accessions of wild barley, Hordeum vulgare ssp. spontaneum, drawn from throughout the species range. The region sequenced included 786 bp of exon sequence (part of exon 4, all of exons 5-9, and part of exon 10) and 576 bp of intron sequence (all of introns 4-9). There were 19 sites polymorphic for nucleotide substitutions, 8 in introns, and 11 in exons. Of the 11 nucleotide substitutions in codons, 4 were synonymous and 7 were nonsynonymous, occurring uniquely in the sample. There was no evidence of recombination in the region studied, and the estimated effective population size (Ne) based on synonymous sites was approximately 1.8-4.2 x 10(5). Several tests reveal that the pattern of nonsynonymous substitutions departs significantly from neutral expectations. However, the data do not appear to be consistent with recovery from a population bottleneck, recent population expansion, selective sweep, or strong positive selection. Though several features of the data are consistent with background selection, the distributions of polymorphic synonymous and intron sites are not perturbed toward a significant excess of rare alleles as would be predicted by background selection.

Alcohol Dehydrogenase↗
PubMed2004

Exact solutions for evolutionary strategies on harmonic landscapes.

In this paper two different evolutionary strategies are tested by means of harmonic landscapes. Both strategies are based on ensembles of searchers, spreading over the search space according to laws inspired by nature. The main difference between the two prototypes is given by the underlying selection mechanism, governing the increase or decrease of the local population of searchers in certain regions of the search space. More precisely, we compare a thermodynamic strategy, which is based on a physically motivated local selection criterion, with a biologically motivated strategy, which features a global selection scheme (i.e., global coupling of the searchers). Confining ourselves to a special class of initial conditions, we show that, in the simple case of harmonic test potentials, both strategies possess particular analytical solutions of the same type. By means of these special solutions, the velocities of the two strategies can be compared exactly. In the last part of the paper, we extend the scope of our discussion to a mixed strategy, combining local and global selection.

Biological Evolution↗
PubMed1984

[Bestrabacil: a possible target-oriented anticancer agent].

Bestrabucil, the benzoate of an estradiol-chlorambucil conjugate, was initially developed as a target-oriented anticancer agent for breast cancers with positive estrogen receptors, by conjugating a tumoricidal agent, chlorambucil, to a vehicle, estradiol. Further studies, however, revealed that regardless of the presence of estrogen receptors, bestrabucil selectively accumulates in malignant tumor cells. The unique feature of bestrabucil, selective affinity to tumor cells, was demonstrated in in vitro and in vivo studies. Significantly larger amounts of 3H-bestrabucil accumulated in malignant cells (3T3-SV40 transformed) than in normal cells (3T3). In vitro inhibition effects of bestrabucil on cell growth was observed only in malignant cells. Selective accumulation of bestrabucil in malignant tumor tissues was also demonstrated in in vivo experiments. After a single oral administration of 100 mg/kg of bestrabucil to female Wistar rats bearing Walker 256 carcinoma, bestrabucil accumulated significantly occurred in tumor tissues with little or no accumulation in normal tissues and blood. Anti-tumor effects and toxicities of bestrabucil and chlorambucil, were compared using Walker 256 carcinoma. Bestrabucil exerted its antitumor effects with little change in leucocyte counts in the peripheral blood, whereas chlorambucil showed significant side effects. Finally, selective accumulation of bestrabucil in malignant tumor tissues, was demonstrated clinically. Tumor specimens obtained during the operation of patients with various types of cancer, 24 hours after oral administration of 100 mg of bestrabucil, contained significantly larger amounts of bestrabucil compared with adjacent normal tissues. Clinical trials of bestrabucil are being carried out at present. Bestrabucil seems to be a promising target-oriented anticancer agent and deserves further investigation.

Administration, Oral↗
PubMed1995

Invariance of textural features in image cytometry under variation of size and pixel magnitude.

Textural features of the granular structure of stained cell nuclei and nuclear sections derived from co-occurrence and run length matrices are often used for correlation with external (clinical) parameters. The representation of cell nuclei and nuclear sections vary considerably under changes of preparation and fixation conditions. Most obvious are changes in size e.g. by fixation as well as changes in the amount of bound stain. Computer-simulated variations in size and pixel magnitude of a set of images of cell nuclei stained with Feulgen were featured and compared. Resulting feature dependencies are used for the setting of parameters of feature extraction procedures as well as for the selection of invariant features for texture quantification of material with variations examined.

Cell Nucleus↗
PubMed1983

Coronary angiographic features in endomyocardial fibrosis.

Selective coronary cineangiography was performed in 24 patients with angiographic features suggestive of endomyocardial fibrosis (EMF). 8 patients had right ventricular disease, 2 had left ventricular disease and 14 had biventricular disease. The abnormal features found in the coronary arteries of these patients were: (a) vascular blush or neovascularity in 54.2% of patients and (b) localized ventricular filling from the region of the blush in 16.7%. Generalized tortuosity of the coronary arteries, considered to be a nonspecific change associated with ventricular enlargement and hypertrophy, was seen in 50%. This study lends support to one of the hypotheses which implies the role of mural thrombus in the evolution of the pathological lesion of EMF.

Adolescent↗
PubMed2001

[A study on quantitative assessment of osteoporosis based on texture analysis].

A quantitative assessment on osteoporosis by using texture analysis has been developed on the basis of coherence mapping, two-dimensional power spectral estimation with modulated transfer function correction and fractal features analysis on trabecular pattern of bone X-ray images. Three objective features of trabecular pattern are selected to form a feature set that can be used in automatic classification for two grades of bone: normal bone and the bone with a medium degree of osteoporosis. This set of features is extracted from each of 16 sample bone X-ray images. With the use of Euclidean norm in the feature space, a center of cluster of each grade of bone is defined as the prototype. For each bone X-ray image, the distance from its features to the two prototypes in feature space is computed to provide an objective judgement on the degree of osteoporosis. The machine classification of 10 bone X-ray images based on the developed prototype is given, and the result indicates that the proposed method is potentially applicable to the objective diagnosis of osteoporosis.

Femur↗
PubMed2005

A study of business letter features.

As part of their work, forensic document examiners examine word processed letters. The purpose of this study, the first of its kind, was to determine how common or rare certain features are in word-processed business letters and if any of these features could determine the author or source. Initially, 114 original business letters were obtained that were dated from 1999 through 2003. Specific features of the letters were selected for examination. These features were letter format, type style, the point size of the font, margin spacing to ascertain the use or nonuse of the default margins for Word (1.25 in. nonjustified) and the default margins for WordPerfect (1 in. nonjustified). In addition, the research involved the examination of the right margins to determine if they were justified or not and the use of the comma or colon in the salutation of the letter. The features of each letter were independently examined by the authors and the findings documented. As expected, several features were found to be very common. For example,full block format was used on 48% of the letters followed by the semi-block with 39%. The Times Family of fonts was used on 67% of the letters. Font point size 12 was the most popular with 70%. The nonjustified default margins were widespread with 67% and the colon was the overwhelming favorite in the salutation with 79%. There were some unexpected findings that could possibly lead to the identification of a source or typist.

Journal Article↗
PubMed1998

Attentional selection by distractor suppression.

Selective attention was studied in displays containing singletons popping out for their odd form or color. The target was defined as the form-singleton, the distractor as the color-singleton. The task was to discriminate the length of a longer line inside the target. Target-distractor similarity was controlled using a threshold measurement as dependent variable in experiments in which distractor presence vs absence, bottom-up vs top-down selection (through knowledge of target features), and target-distractor distance were manipulated. The results in the bottom-up condition showed that length threshold was elevated when a distractor was present and that this elevation progressively increased as the number of distractors was increased from one to two. This set-size effect was not accounted by the hypothesis that selective attention intervenes only at the stage of decision before response. Selective attention produced a suppressive surround in which discriminability of neighboring objects was strongly reduced, and a larger surround in which discriminability was reduced by an approximately constant amount. Different results were found in the top-down condition in which target discriminability was unaffected by distractor presence and no effect of target-distractor distance was found. On the other hand, response times in both bottom-up and top-down conditions were slower the shorter the target-distractor distance was. On the basis of the experimental results, selective attention is a parallel process of spatial filtering at an intermediate processing level operating after objects have been segmented. This filtering stage explores high level interactions between objects taking control on combinatorial explosion by operating over only a limited spatial extent: it picks out a selected object and inhibits the neighboring objects; then, non-selected objects are suppressed across the overall image. When no feature-based selection is available in the current behavior, this filtering influences perception in decreasing discriminability of non-selected objects. When feature-based selection is available, spatial interactions are set before stimulus arrival, hence only the unmatching objects have their discriminability diminished.

Attention↗
PubMed1988

Neuropharmacological analysis of the role of indoleamine-accumulating amacrine cells in the rabbit retina.

In order to elucidate the role of putative indoleaminergic amacrine cells in visual processing, we have employed pharmacological agents specific for the two classes of serotonin receptor, 5-HT2 and 5-HT1, which have been identified in both the retina and brain. Perfusion of the rabbit retina with 5-HT2 selective antagonists decreases the ON-excitation of all classes of ganglion cell as well as the spontaneous activity of these cells. The effect on OFF-responses depends on the cell type: OFF-excitation of center-surround brisk and sluggish cells is increased or not affected by these drugs, but OFF excitation of ON/OFF direction selective cells is reduced. No disruption of the trigger features of direction selective or orientation selective cells was discovered, suggesting that indoleaminergic amacrine cells do not play a role in the generation of the complex properties of these cells. 5-HT1 receptors are heterogeneous and classified as a, b, or c subtypes. Since no selective antagonists are available for these sites, we have employed specific agonists. The most specific of these are for the 5-HT1A receptor. Perfusion with these agonists had physiological effects similar to those with perfusion of 5-HT2 antagonists. Thus, we have suggested that these two classes of serotonin receptors mediate opponent processes in the neural pathway. Since indoleaminergic cells make reciprocal synaptic connections with rod bipolar cell terminals, which are depolarizing in the rabbit retina, we hypothesize that 5-HT2 receptors facilitate the synaptic transmission from the depolarizing rod bipolar cell thus facilitating ON-excitation in the retinal network while 5-HT1A receptors mediate an inhibitory process. Similar self-opponent processing appears to take place in the hypothalamic and hippocampal serotonergic systems as well as in the dopaminergic retinal system. Thus, it is likely that this organization is a general feature of monoamine signal transmission in the central nervous system.

Animals↗
PubMed2003

Strategies leading to MT2 selective melatonin receptor antagonists.

Studies of the physiological actions of melatonin have been hindered by the lack of specific, potent and subtype selective agonists and antagonists. This paper reviews our progress in developing subtype selective melatonin antagonists. Evidence is presented suggesting the structural features conferring MT2 selective antagonism.

Animals↗
PubMed2003

Multiwavelet grading of pathological images of prostate.

Histological grading of pathological images is used to determine level of malignancy of cancerous tissues. This is a very important task in prostate cancer prognosis, since it is used for treatment planning. If infection of cancer is not rejected by non-invasive diagnostic techniques like magnetic resonance imaging, computed tomography scan, and ultrasound, then biopsy specimens of tissue are tested. For prostate, biopsied tissue is stained by hematoxyline and eosine method and viewed by pathologists under a microscope to determine its histological grade. Human grading is very subjective due to interobserver and intraobserver variations and in some cases difficult and time-consuming. Thus, an automatic and repeatable technique is needed for grading. Gleason grading system is the most common method for histological grading of prostate tissue samples. According to this system, each cancerous specimen is assigned one of five grades. Although some automatic systems have been developed for analysis of pathological images, Gleason grading has not yet been automated; the goal of this research is to automate it. To this end, we calculate energy and entropy features of multiwavelet coefficients of the image. Then, we select most discriminative features by simulated annealing and use a k-nearest neighbor classifier to classify each image to appropriate grade (class). The leaving-one-out technique is used for error rate estimation. We also obtain the results using features extracted by wavelet packets and co-occurrence matrices and compare them with the multiwavelet method. Experimental results show the superiority of the multiwavelet transforms compared with other techniques. For multiwavelets, critically sampled preprocessing outperforms repeated-row preprocessing and has less sensitivity to noise for second level of decomposition. The first level of decomposition is very sensitive to noise and, thus, should not be used for feature extraction. The best multiwavelet method grades prostate pathological images correctly 97% of the time.

Algorithms↗
PubMed2004

Negative and positive congruence effects in letters and shapes.

In six experiments in which a binary classification task was used, letter and nonletter (geometrical shapes, pseudoletters, or rotated letters) targets were presented either in isolation or surrounded by a geometrical shape. The surrounding shape could be congruent or incongruent with the target. When the classification required a distinction between letters and nonletters, either explicitly (Experiments 1-3) or implicitly (Experiment 4), a negative congruence effect was obtained for letters, contrasting with a regular, positive congruence effect for nonletters. When no distinction was to be made, letters and nonletters invariably showed a positive congruence effect (Experiments 5 and 6). In particular, between Experiments 1-4 and Experiments 5 and 6, the occurrence of negative or positive congruence effects for the same stimuli depended on the task. Feature interaction, target selection, and response competition explanations were tested against a feature integration approach. The results are explained in terms of different feature integration strategies for letters and nonletters.

Adult↗
PubMed1995

Sm and DNA binding by dual reactive B cells requires distinct VH, V kappa, and VH CDR3 structures.

We have previously demonstrated an overlap of the anti-Sm and anti-DNA responses in MRL/Mp-lpr/lpr mice. The Ab produced by many anti-Sm hybridomas bind DNA and are encoded by Ig V genes used by anti-DNA hybridomas. In addition, some anti-Sm Ab that bind DNA have acquired mutations that improve DNA binding, indicating that DNA is a selecting Ag in the anti-Sm response. To gain insight into the basis for the dual binding ability of these Ab, we coexpressed the H chain from the anti-Sm hybridoma 2-12 with nine different L chains. Hybridoma 2-12 binds Sm but not DNA, yet expresses the same J558 VH gene as three anti-Sm hybridomas that bind ssDNA and at least one anti-DNA hybridoma that does not bind Sm. We found that most of the transfectoma Ab bind Sm, but their avidities vary over more than 3 orders of magnitude. Five of the nine transfectoma Ab bind ssDNA, and none bind dsDNA. In general, the ability to bind each Ag follows the binding ability of the hybridoma from which the L chain is derived. H Chain swapping experiments indicate that the H chain, VH CDR3 in particular, contributes to the binding of both Sm and DNA. We conclude that Sm and DNA select for distinct features of VH, V kappa, and VH CDR3, suggesting selection by both Ag in the anti-Sm response.

Amino Acid Sequence↗