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At least 379 records · Page 21Linked to original sources
PubMed2004

The roles of distractor noise and target certainty in search: a signal detection model.

Observers searched arrays of briefly presented near-isoluminant colored disks for a single disk of known color (feature search) or unknown color (oddity search). Speed and accuracy were converted to a single, model-based measure of performance (Perf), in units of (d')2 per second of latency. Perf decreased with set size in feature search and increased in oddity. In both types of search, grouping the distractors, making them homogeneous in color, and reducing their saturation, all increased Perf. These commonalities suggested an SDT-based model in which distractors increase noise in the same way in both types of search. However, in oddity, though not in feature search, distractors must be attended and so adding distractors also boosts the effective target contrast, overcoming the added noise. A model with two free parameters for noise and one for attention accounted for every combination except for oddity searches among heterogeneous grouped distractors.

Adolescent↗
PubMed2000

Reformulating attention-deficit/hyperactivity disorder according to signal detection theory.

OBJECTIVE: The current diagnostic algorithm for attention-deficit/hyperactivity disorder (ADHD) is not highly predictive of impairment and yields low interrater agreement. The objective of this study was to enhance the diagnostic accuracy of ADHD by identifying the symptoms that are associated with impairment. METHOD: Semistructured interviews and impairment rating scales were administered to parents and teachers of 218 children. Combinations of ADHD symptoms were examined according to a receiver operating characteristic (ROC) based procedure to create diagnostic algorithms that predict impairment. RESULTS: In comparison with the DSM-IV, the ROC-based algorithms were 2 to 3 times more efficient in discriminating impaired from nonimpaired children. Parent and teacher agreement was also 3 times higher. CONCLUSIONS: Limiting the diagnosis to symptoms that predict impairment can increase the validity of the ADHD diagnosis. Results also support the use of ROC analyses in developing better diagnostic algorithms.

Algorithms↗
PubMed1997

Novel detection system of flow injection analysis (1). The existence of significant relation between secondary structure of DNA and sensitivity in signal detection.

Polymerase Chain Reaction (PCR) products was detected quantitatively using a flow injection type sensor, based on Surface Plasmon Resonance (SPR). We used asymmetric PCR to amplify the two kinds of products; their DNA lengths are different. This novel design permitted us not only to detect PCR products with high-sensitivity, but also to develop a rapid DNA detection system for the sense of the genetic pathogen.

Bacterial Toxins↗
PubMed2003

Characteristics of microembolic signals detected near their origins in middle cerebral artery stenoses.

BACKGROUND AND PURPOSE: Usually, microembolic signal (MES) monitoring is performed for MESs arising from downstream sources. The aim of this study is to describe the special characteristics of MESs originating from nearby sources in the middle cerebral artery (MCA). METHODS: We analyzed 265 MESs detected in 5 patients (the study group) who had acute ischemic strokes within the territory of MCA stenoses and 48 MESs detected in 7 patients (the control group) from proximal sources: severe internal carotid artery stenoses and prosthetic heart valves. MESs were recorded with a 2-MHz, bigate transducer. We performed offline analyses of the recorded MESs using both post-fast Fourier transform (FFT) spectra and pre-FFT time domain signals. MESs were divided into 3 types--focused-frequency signals (FFSs), bottom-frequency signals (BFSs), and multifrequency signals (MFSs)--according to the frequencies of the signals displayed on the post-FFT spectra. RESULTS: In the study group, among 265 MESs, 245 (92.5%) were MFSs, 11 (4.2%) were FFSs, and 9 (3.4%) were BFSs. In the control group, among 48 MESs, 45 (93.5%) were FFSs, 2 (4.2%) were MFSs, and 1 (2.%) was a BFS. There was significant difference in MES type between MCA stenoses and other embolic sources (P < .05). On the post-FFT spectra, MFSs recorded from MCA stenoses occupied multiple frequencies along the vertical axis, and the low-frequency parts were usually bidirectional. On the pre-FFT time domain signals, the highest frequency parts presented distorted, amplitude-modulated sine waves, and the low-frequency parts presented totally irregular waves. The amplitudes of the low-frequency parts diminished with time in the proximal channel but enlarged with time in the distal channel over a short period. CONCLUSION: MESs recorded from MCA stenoses may have special characteristics of multiple frequencies on both post-FFT spectra and pre-FFT time domain signals. Our findings may represent rotating or vibrating emboli as they are just dislodged from the thrombus and are moving from the vessel wall to the center. Further clinical and laboratory studies are needed to confirm this hypothesis.

Aged↗
PubMed2005

Diffuse large B-cell lymphoma with extra Bcl-2 gene signals detected by FISH analysis is associated with a "non-germinal center phenotype".

Amplification and translocation of the Bcl-2 gene has been detected in a certain subset of diffuse large B-cell lymphomas (DLBCL). The correlations among Bcl-2 protein expression, gene translocation or amplification, and the molecular signature determined by cDNA array are poorly understood. This study examined 25 cases with de novo nodal DLBCL. Interphase fluorescence in situ hybridization (FISH) analysis was performed to evaluate the Bcl-2 gene using IGH/BCL2 and CEP18 centromere probes (Vysis). When extra Bcl-2 gene signals were observed in each tumor cell and when these signals were in proportion to the extra CEP18 probe signals, we regarded the findings as indicating the presence of an additional chromosome 18; when extra Bcl-2 signals were observed but additional CEP18 signals were not, we regarded the findings as indicating the presence of gene amplification. A panel of 3 antigens (CD10, Bcl-6, and MUM-1) was applied to categorize each case as either a "germinal center B-cell (GCB) phenotype" or a "non-GCB phenotype." Of the 25 cases examined, 8 cases (32%) were classified as "GCB phenotype" and 17 cases (68%) were classified as "non-GCB phenotype." A FISH analysis revealed that t(14;18) was detected in 2 of the 8 cases (25%) with the "GCB phenotype" but in none of the 17 "non-GCB phenotype" cases. Extra Bcl-2 gene signals were detected in 7 of the 25 (28%) cases examined: n = 5 for an additional chromosome 18, n = 1 for gene amplification, and n = 1 for additional chromosome 18 + gene amplification. Extra Bcl-2 gene signals were exclusively detected in DLBCL with the "non-GCB phenotype"; these cases, with the exception of one, stained strongly positive for Bcl-2. The DLBCLs with Bcl-2 protein overexpression were classified into at least two heterogeneous molecular groups, based on the results of the FISH analysis.

Adult↗
PubMedDate not supplied

Sensitive fluorescence in situ hybridization signal detection in maize using directly labeled probes produced by high concentration DNA polymerase nick translation.

The signal produced by fluorescence in situ hybridization (FISH) often is inconsistent among cells and sensitivity is low. Small DNA targets on the chromatin are difficult to detect. We report here an improved nick translation procedure for Texas red and Alexa Fluor 488 direct labeling of FISH probes. Brighter probes can be obtained by adding excess DNA polymerase I. Using such probes, a 30 kb yeast transgene, and the rp1, rp3 and zein multigene clusters were clearly detected.

Chromosomes, Plant↗
PubMed2002

Interfaces between the detection, signaling, and repair of DNA damage.

Left unrepaired, the myriad types of damage that can occur in genomic DNA pose a serious threat to the faithful transmission of the correct complement of genetic material. Defects in DNA damage signaling and repair result in genomic instability, a hallmark of cancer, and often cause lethality, underlining the importance of these processes in the cell and whole organism. The past decade has seen huge advances in our understanding of how the signal transduction pathways triggered by DNA damage radically alter cell behavior. In contrast, it is still unclear how primary DNA damage is detected and how this interfaces with signal transduction and DNA repair proteins.

Animals↗
PubMed1991

Loss of atrial signal detection with increasing sensitivity settings: a software problem and its practical solution.

A logic error in the software of Cosmos II results in apparent malsensing of atrial signals at high rather than low sensitivity settings. The paradoxical function was found in 54 out of 87 units tested (= 62%) if the atrial sensitivity was increased and in 54 out of 87 units tested (= 62%) if the atrial sensitivity was increased and the ventricular refractory period was lengthened beyond critical limits that could be defined individually. The problem inherent in both unipolar (66%) and bipolar systems (54%) is attributed to a summation of a physiological signal and internal noise, which has to be detected at the atrial level within a specific timing window to disable atrial sensing for the next pacing cycle. The malfunction virtually disappears if the ventricular refractory period does not exceed 210 msec. It is recommended, therefore, that Cosmos II pacemakers be left at their nominal ventricular refractory value (200 msec).

Adult↗
PubMed2001

[Weak signal detection in every heart cycle].

In this article, a new approach is introduced to lowering the myo-electronic noise in weak ECG signals. We use artificial neural network to make the noise be white, and then we adopt an adaptive filter of which the reference signal is achieved by extracting from other ECG cycle. The outcome is the reduction of both white noise and non-white noise in ECG signal. Satisfactory results have been achieved by using this method in the experiment of late potential detection.

Action Potentials↗
PubMed2006

Analysis of the effects of disk tilt on the differential-phase-detection signal in a high-density DVD read-only disk driver.

A high-density DVD (HD-DVD) is one of the high-density optical storage technology newly designed to meet the demands of high-definition video broadcasting that is very sensitive to the radial tilt of a disk. An analytic model based on diffraction theory is presented in detail to calculate the tracking error signal of a HD-DVD read-only disk driver by using the differential-phase-detection (DPD) method when radial tilt of a disk occurs. The effects of the tilt on a DPD signal in a HD-DVD read-only disk driver are quantified and compared to those in a DVD read-only disk driver. Experimental measurements for the DPD signal under different radial tilt angles in a HD-DVD read-only disk driver are also reported.

Journal Article↗
PubMed2006

Simulation of intramuscular EMG signals detected using implantable myoelectric sensors (IMES).

The purpose of this study was to test the feasibility of recording independent electromyographic (EMG) signals from the forearm using implantable myoelectric sensors (IMES), for myoelectric prosthetic control. Action potentials were simulated using two different volume conductor models: a finite-element (FE) model that was used to explore the influence of the electrical properties of the surrounding inhomogeneous tissues and an analytical infinite volume conductor model that was used to estimate the approximate detection volume of the implanted sensors. Action potential amplitude increased progressively as conducting electrodes, the ceramic electrode casing and high resistivity encapsulation tissue were added to the model. For the muscle fiber locations examined, the mean increase in EMG root mean square amplitude when the full range of material properties was included in the model was 18.2% (+/-8.1%). Changing the orientation of the electrode with respect to the fiber direction altered the shape of the electrode detection volume and reduced the electrode selectivity. The estimated detection radius of the IMES electrode, assuming a cylindrical muscle cross section, was 4.8, 6.2, and 7.5 mm for electrode orientations of 0 degree, 22.5 degrees, and 45 degrees with respect to the muscle fiber direction.

Action Potentials↗
PubMed2001

A novel approach for precise simulation of the EMG signal detected by surface electrodes.

We propose a new electromyogram generation and detection model. The volume conductor is described as a nonhomogeneous (layered) and anisotropic medium constituted by muscle, fat and skin tissues. The surface potential detected in space domain is obtained from the application of a two-dimensional spatial filter to the input current density source. The effects of electrode configuration, electrode size and inclination of the fibers with respect to the detection system are included in the transfer function of the filter. Computation of the signal in space domain is performed by applying the Radon transform; this permits to draw considerations about spectral dips and clear misunderstandings in previous theoretical derivations. The effects of generation and extinction of the action potentials at the fiber end plate and at the tendons are included by modeling the source current, without any approximation of its shape, as a function of space and time and by using again the Radon transform. The approach, based on the separation of the temporal and spatial properties of the muscle fiber action potential and of the volume conductor, includes the capacitive tissue properties.

Action Potentials↗
PubMed2003

Signal detection and target gene induction by the CpxRA two-component system.

The Cpx pathway is a two-component signal transduction system that senses a variety of envelope stresses, including misfolded proteins, and responds by upregulating periplasmic folding and trafficking factors. CpxA resides in the inner membrane and has both kinase and phosphatase activities. CpxR, the response regulator, mediates a response by activating transcription of stress-combative genes. Signal transduction is subject to feedback inhibition via regulon member CpxP and autoamplification. Recently, it was shown that the Cpx pathway is also upregulated when cells adhere to hydrophobic surfaces and that this response is dependent on the outer membrane lipoprotein NlpE. Here we show that while NlpE is required for induction of the Cpx pathway by adhesion, induction by envelope stress and during growth is NlpE independent. We show that while all of the envelope stresses tested induce the Cpx pathway in a manner that is dependent on the periplasmic domain of CpxA, induction during growth is independent of CpxA. Therefore, we propose that the Cpx pathway can sense inducing cues that enter the signaling pathway at three distinct points. Although CpxP is not required for induction of the Cpx pathway, we show that its activity as a negative regulator of CpxA is inactivated by envelope stress. Moreover, the cpxP promoter is more inducible than any other regulon member tested. Consistent with these results, we suggest that CpxP performs a second function, most likely that of a chaperone. Finally, we show that two Cpx-regulated genes are differentially upregulated in response to different envelope stresses, suggesting the existence of three stress-responsive systems.

Adaptation, Physiological↗
PubMed2001

Microembolic signal detection in patients with symptomatic and asymptomatic lone atrial fibrillation.

BACKGROUND AND PURPOSE: There are few data on the occurrence of microembolic signals (MES) in patients with lone atrial fibrillation (LAF). The aim of this work was to systematically study the frequency of MES in patients with symptomatic and asymptomatic LAF and to compare it with that of nonvalvular atrial fibrillation (NVAF). METHODS: 37 consecutive acute stroke patients with LAF, 10 asymptomatic patients with LAF and 100 age-matched healthy controls were studied. Another 92 stroke patients with known NVAF were included in the study to compare patients with LAF regarding the presence of MES. Both middle cerebral arteries were monitored by transcranial Doppler ultrasound for at least 30 min at admission and after 1 week in symptomatic and asymptomatic patients with LAF. All patients with LAF were followed up for a mean duration of 18 months, and recurrent strokes were registered. RESULTS: MES was detected in 11 (29%) symptomatic patients with LAF but only in 1 asymptomatic patient with LAF (chi(2) = 11.3; p = 0.0008) and in no control subjects (chi(2) = 106; p = 0.00001). There was no difference in the frequency of MES-positive patients and the number of MES between subjects with symptomatic LAF and known NVAF (29% in both groups; mean count, 16 +/- 4 vs. 17 +/- 6; p = 0.73). In patients with symptomatic LAF and NVAF who underwent anticoagulant therapy, there was no difference in the frequency of MES after 1 week of hospitalization (chi(2) = 1.53; p = 0.2). During a mean follow-up period of 18 months, 1 patient with symptomatic LAF and MES had a recurrent ischemic event 1 year after the first stroke and none of those with asymptomatic LAF had any events. CONCLUSION: Our study suggests that asymptomatic and paroxysmal LAF with a lower frequency of MES is a benign disorder compared to chronic and symptomatic LAF with a higher frequency of MES. Further studies need to justify whether MES has a predictive value in patients with chronic LAF who are prone to ischemic stroke.

Adult↗
PubMed2001

Robust stochastic resonance: signal detection and adaptation in impulsive noise.

Stochastic resonance (SR) occurs when noise improves a system performance measure such as a spectral signal-to-noise ratio or a cross-correlation measure. All SR studies have assumed that the forcing noise has finite variance. Most have further assumed that the noise is Gaussian. We show that SR still occurs for the more general case of impulsive or infinite-variance noise. The SR effect fades as the noise grows more impulsive. We study this fading effect on the family of symmetric alpha-stable bell curves that includes the Gaussian bell curve as a special case. These bell curves have thicker tails as the parameter alpha falls from 2 (the Gaussian case) to 1 (the Cauchy case) to even lower values. Thicker tails create more frequent and more violent noise impulses. The main feedback and feedforward models in the SR literature show this fading SR effect for periodic forcing signals when we plot either the signal-to-noise ratio or a signal correlation measure against the dispersion of the alpha-stable noise. Linear regression shows that an exponential law gamma(opt)(alpha)=cA(alpha) describes this relation between the impulsive index alpha and the SR-optimal noise dispersion gamma(opt). The results show that SR is robust against noise "outliers." So SR may be more widespread in nature than previously believed. Such robustness also favors the use of SR in engineering systems. We further show that an adaptive system can learn the optimal noise dispersion for two standard SR models (the quartic bistable model and the FitzHugh-Nagumo neuron model) for the signal-to-noise ratio performance measure. This also favors practical applications of SR and suggests that evolution may have tuned the noise-sensitive parameters of biological systems.

Journal Article↗
PubMed1988

[The suction signal detected by color Doppler echocardiography in patients with mitral regurgitation: its clinical significance].

The present study clarified the clinical significance of the suction signal--regurgitant signal near the mitral valve in the left ventricle--as obtained by two-dimensional color Doppler echocardiography in patients with mitral regurgitation. The study population consisted of 39 patients with various heart diseases having mitral regurgitation. The presence of a mitral regurgitant signal was determined not only in the left atrium but in the left ventricle using the long-axis view, four-chamber view, and short-axis view. 1. The suction signal was observed in 17 cases; on the posteromedial commissure side in four; the central portion in seven; the anterolateral commissure side in five and the mitral aneurysm portion in one. The site of the suction signal indicated the mitral regurgitant orifice and was useful for identifying the regurgitant orifice particularly in cases with prolapse of the commissural scallop. 2. Left ventriculography was performed in 18 cases and the severity of mitral regurgitation was grade III/IV or IV/IV in seven of eight cases with suction signals and was grade II/IV in the remaining one, while it was grade II/IV or I/IV in all ten cases without the signal. Sensitivity was then 100% and specificity was 91% in diagnosing III/IV or greater regurgitation according to the presence of the suction signal. The left atrial jet distance, width and area in the 17 cases with suction signals were significantly greater than those of 22 cases without the signal (3.3 +/- 1.0 vs 1.9 +/- 0.7 cm, 1.4 +/- 0.7 vs 0.8 +/- 0.4 cm, and 4.2 +/- 2.8 vs 1.3 +/- 1.3 cm2, respectively). Thus, the suction signal in the left ventricle in mitral regurgitation provided useful information concerning not only the identification of a regurgitant orifice, but the grade of mitral regurgitation, as well.

Adult↗
PubMed2004

Postmarketing surveillance of potentially fatal reactions to oncology drugs: potential utility of two signal-detection algorithms.

PURPOSE: Several data mining algorithms (DMAs) are being studied in hopes of enhancing screening of large post-marketing safety databases for signals of novel adverse events (AEs). The objective of this study was to apply two DMAs to the United States FDA Adverse Event Reporting System (AERS) database to see whether signals of potentially fatal AEs with cancer drugs might have been identified earlier than with traditional methods. METHODS: Screening algorithms used for analysis were the multi-item gamma Poisson shrinker (MGPS) and proportional reporting ratios (PRRs). Data mining was performed on data from the FDA AERS database. When a signal was identified, it was compared with that in the year in which the event was added to package insert and/or the year a "case series" was published. A recent publication summarizing the time of dissemination of information on potentially fatal AEs to cancer drugs provided the data set for analysis. RESULTS: The peer-reviewed published analysis contained 21 drugs and 26 drug-event combinations (DECs) that were considered sufficiently specific for data mining. Twenty-four of the DECs generated a signal of disproportionate reporting with PRRs (6 at 1 year and 16 from 2 years to 18 years prior to either a published "case series" or a package insert change) and 20 with MGPS (3 at 1 year and 11 from 2 years to 16 years prior to either a published "case series" or a package insert change). Two DECs did not signal with either DMA. CONCLUSION: At least one commonly cited DMA generated a signal of disproportionate reporting for 24 of 26 DECs for selected cancer drugs. For 16 DECs, one could conclude that a signal was generated well in advance (> or =2 years) of standard techniques in use with at least one DMA. DMAs might be useful in supplementing traditional surveillance strategies with oncology drugs and other drugs with similar features. (i.e., drugs that may be approved on an accelerated basis, are known to have serious toxicity, are administered to patients with substantial and complicated comorbid illness, are not available to the general medical community, and may have a high frequency of "off-label" use).

Adverse Drug Reaction Reporting Systems↗