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Results for “Signal detection”

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At least 343 records · Page 19Linked to original sources
PubMedDate not supplied

Markov encoding for detecting signals in genomic sequences.

We present a technique to encode the inputs to neural networks for the detection of signals in genomic sequences. The encoding is based on lower-order Markov models which incorporate known biological characteristics in genomic sequences. The neural networks then learn intrinsic higher-order dependencies of nucleotides at the signal sites. We demonstrate the efficacy of the Markov encoding method in the detection of three genomic signals, namely, splice sites, transcription start sites, and translation initiation sites.

Base Sequence↗
PubMed1989

VLSI processors for signal detection in SETI.

The objective of the Search for Extraterrestrial Intelligence (SETI) is to locate an artificially created signal coming from a distant star. This is done in two steps: (1) spectral analysis of an incoming radio frequency band, and (2) pattern detection for narrow-band signals. Both steps are computationally expensive and require the development of specially designed computer architectures. To reduce the size and cost of the SETI signal detection machine, two custom VLSI chips are under development. The first chip, the SETI DSP Engine, is used in the spectrum analyzer and is specially designed to compute Discrete Fourier Transforms (DFTs). It is a high-speed arithmetic processor that has two adders, one multiplier-accumulator, and three four-port memories. The second chip is a new type of Content-Addressable Memory. It is the heart of an associative processor that is used for pattern detection. Both chips incorporate many innovative circuits and architectural features.

Astronomy↗
PubMed1990

Vestibular receptor cells and signal detection: bioaccelerometers and the hexagonal sampling of two-dimensional signals.

The inner ear contains sensory organs which signal changes in head movement. The vestibular sacs, in particular, are sensitive to linear accelerations. Electron microscopic images have revealed the structure of tiny sensory hair bundles, whose mechanical deformation results in the initiation of neuronal activity and the transmission of electrical signals to the brain. The structure of the hair bundles is shown in this paper to be that of the most efficient two-dimensional phased-array signal processors.

Acceleration↗
PubMed2005

Threshold nonlinearities and signal detection theory.

The review summarizes Kulikowski's contributions to the mechanisms involved in visual detection and discrimination. His findings provide strong evidence for the existence of 'barriers' which block weak activity in the visual system. It is proposed that the properties of these barriers may underlie near-optimal detection in conditions of signal uncertainty.

Discrimination, Psychological↗
PubMed2003

Signal detection via residence times statistics: noise-mediated minimization of the measurement error.

We study the problem of detecting a small dc signal by quantifying its effect on the mean difference DeltaT in residence times in the stable steady states of a bistable dynamical measurement device, in the presence of a noise floor and a known time-sinusoidal bias signal. Errors in the measurement process occur due to a finite observation time that is present in most practical scenarios. The error is found to have a nonmonotonic dependence on the noise intensity; at a critical noise intensity, the error is minimized. This phenomenon, reminiscent of the well-known stochastic resonance effect, can also be obtained by adjusting the device tuning parameters for a given noise floor. The effect appears to be most pronounced for subthreshold bias signals in the strongly nonlinear response regime.

Journal Article↗
PubMed1992

Optimum nonlinear signal detection and estimation in the presence of ultrasonic speckle.

A unified approach to the design of nonlinear filters for speckle suppression in ultrasound B-mode images is presented. The detection of the (lesion) signal is formulated as a binary hypothesis-testing problem. The structure of the optimal decision rules is derived both in the case where the lesion signal is assumed either a constant or random variable. In the case of a constant signal, the maximum likelihood (ML) estimator and the optimal L-estimator are derived. In the case of a random lesion signal, the maximum a posteriori probability estimator of the lesion signal has also been found. Experimental results verify the superiority of the proposed ML-estimator and the L-estimator over the straightforward choice of an arithmetic mean for speckle filtering in simulated tissue mimicking phantom ultrasound B-mode images.

Equipment Design↗
PubMed1997

Principles of signal detection in pharmacovigilance.

Adverse drug effects are manifold and heterogenous. Many situations may hamper the signalling (i.e. the detection of early warning signs) of adverse effects and new signals often differ from previous experiences. Signals have qualitative and quantitative aspects. Different categories of adverse effects need different methods for detection. Current pharmacovigilance is predominantly based on spontaneous reporting and is mainly helpful in detecting type B effects (those effects that are often allergic or idiosyncratic reactions, characteristically occurring in only a minority of patients and usually unrelated to dosage and that are serious, unexpected and unpredictable) and unusual type A effects (those effects that are related to the pharmacological effects of the drug and are dosage-related). Examples of other sources of signals are prescription event monitoring, large automated data resources on morbidity and drug use (including record linkage), case-control surveillance and follow-up studies. Type C effects (those effects related to an increased frequency of 'spontaneous' disease) are difficult to study, however, and continue to pose a pharmacoepidemiological challenge. Seven basic considerations can be identified that determine the evidence contained in a signal: quantitative strength of the association, consistency of the data, exposure response relationship, biological plausibility, experimental findings, possible analogies and the nature and quality of the data. A proposal is made for a standard signal management procedure at pharmacovigilance centres, including the following steps: signal delineation, literature search, preliminary inventory of data, collection of additional information, consultation with the World Health Organization Centre for International Drug Monitoring and the relevant drug companies, aggregated data assessment and a report in writing. A better understanding of the conditions and mechanisms involved in the detection of adverse drug effects may further improve strategies for pharmacovigilance.

Adverse Drug Reaction Reporting Systems↗
PubMed1993

Transcription pausing signal detected by sense/antisense transcription.

We studied elongation pausing during transcription in vitro on both the sense and the antisense strands of a given gene fragment(5' end of the bla gene of Tn3). The average transcription rate on the sense strand was much lower than that of the antisense strand, and several pauses observed on the former have no detectable antisense partner. A pausing signal was identified, associated with an (AT)6 sequence, in the vicinity of a strong pause on the sense strand and the sole detected pause on the antisense strand. Mutation of this sequence strongly reduced, by a common factor, pausing times at both sites.

Base Sequence↗
PubMed1999

Clinical application of asymptomatic embolic signal detection in acute stroke: a prospective study.

BACKGROUND AND PURPOSE: The detection of asymptomatic embolization with the use of Doppler ultrasound has a number of potential applications in patients with acute stroke. It may provide information on the stroke pathogenesis in individual cases, identify patients with continued embolization, and allow localization of the active embolic source. METHODS: We recruited 119 patients with acute anterior circulation infarction within 72 hours of stroke onset. Transcranial Doppler recordings were possible in 100 (84.0%). Bilateral 1-hour middle cerebral artery (MCA) recordings were made and saved on digital audiotape for blinded offline analysis. When embolic signals were detected during screening of the first recording, simultaneous recording was performed from the ipsilateral MCA and common carotid artery for an additional 30 minutes. In all patients with embolic signals at screening and in matched negative controls, recordings were repeated on days 4, 7, and 14. RESULTS: Embolic signals were detected in the symptomatic MCA in 16 patients (16%). They were more common in patients with carotid stenosis (P<0.0001), occurring in 50% of this group. They were rare in patients with cardioembolic stroke (4.5%) and were not detected in patients with lacunar stroke. In the 16 patients with embolic signals, the proportion with embolic signals fell over time (P=0. 0025), but they were still present in a third at 2 weeks. In 10 patients, localization of the embolic source was possible by simultaneous recording from the MCA and the ipsilateral common carotid artery. CONCLUSIONS: Continued asymptomatic embolization is common after stroke in patients with carotid artery disease and is still present in a significant proportion at 2 weeks. The technique may identify patients at risk of further stroke for more aggressive antiplatelet therapy; this needs to be tested in large prospective studies. The technique may also allow localization of the active embolic source.

Acute Disease↗
PubMed1996

Effects of masker gating for signal detection in unmodulated and modulated bandlimited noise.

Thresholds for a 400-ms 1000-Hz pure-tone signal were obtained as a function of masking noise bandwidth for unmodulated and square wave modulated masking noise. Rates of modulation were 10 and 40 Hz. Noise bandwidths were 128 Hz, 387 Hz, 921 Hz, and 1505 Hz. The masking noise was either continuous or gated on and off with the signal. In general, signal thresholds were relatively constant as a function of noise bandwidth in unmodulated noise, and improved as a function of increasing noise bandwidth in modulated noise. Noise gating had little or no effect on signal threshold in unmodulated noise. At the 10-Hz modulation rate, signal thresholds were somewhat higher in gated than in continuous noise at relatively narrow noise bandwidths, but thresholds were similar in gated and continuous noise for relatively wide noise bandwidths. At bandwidths of 387, 921, and 1505 Hz, comodulation masking release (CMR) was calculated as the unmodulated noise threshold minus the modulated noise threshold, corrected by the difference between the unmodulated noise threshold and the modulated noise threshold at the 128-Hz bandwidths. At wide masker bandwidth, CMRs were higher for gated noise than for continuous noise. This was due almost entirely to the threshold gating effect found in the 128-Hz bandwidth condition. These results suggested that there was a within-channel effect for gated noise thresholds to be higher than continuous noise thresholds, but essentially no across-channel effect of gating. At the 40-Hz modulation rate, signal thresholds were similar for gated and continuous noise at all noise bandwidths. There was a very small but significant' effect for the gated noise threshold to be lower than the continuous noise threshold at the widest noise bandwidth. It was speculated that this effect may be related to a decrease in sensitivity to modulation with continuous stimulation. In general, effects of gating appear to be small or absent for across-channel masking release in broadband modulated masking noise.

Adult↗
PubMed2006

Signal detection, modularity, and the correlation between extrinsic and intrinsic noise in biochemical networks.

We present an expression for the power spectrum of the output signal of a biochemical network, which reveals that the reactions that allow a network to detect biochemical signals, induce correlations between the extrinsic noise of the input signals and the intrinsic noise of the reactions that form the network. We show that anticorrelations between the extrinsic and intrinsic noise enhance the robustness of zero-order ultrasensitive networks to biochemical noise. We discuss the consequences for a modular description of noise transmission using the mitogen-activated protein kinase cascade.

Biochemistry↗
PubMed2002

13C NMR signal detection of iron-bound cyanide ions in ferric cyanide complexes of heme proteins.

13CN ion appears to have the greatest potential to probe the heme environment of the ferric heme proteins; however, a resonance of the iron-bound (13)CN ion in ferric heme proteins has not yet been located. We show here the first detection of (13)C NMR signals of the iron-bound (13)CN for heme proteins and their model complexes in an unexpectedly large upfield region. This study demonstrates that the (13)C NMR signal of the iron-bound (13)CN is a sensitive probe to study the nature of the proximal ligand in ferric heme protein.

Animals↗
PubMed1984

Visual signal detection. I. Ability to use phase information.

We present experimental evidence that humans use phase information for detection and discrimination of visual signals (static sine waves) when sufficient a priori information is made available. Under these conditions human performance exceeds that of the best-possible phase-insensitive detector. There is a marked reduction in performance when signal-phase information is not given to the observer.

Attention↗
PubMed2005

Unraveling the attentional functions of cortical cholinergic inputs: interactions between signal-driven and cognitive modulation of signal detection.

Neurophysiological studies demonstrated that increases in cholinergic transmission in sensory areas enhance the cortical processing of thalamic inputs. Cholinergic activity also suppresses the retrieval of internal associations, thereby further promoting sensory input processing. Behavioral studies documented the role of cortical cholinergic inputs in attentional functions and capacities by demonstrating, for example, that the integrity of the cortical cholinergic input system is necessary for attentional performance, and that the activity of cortical cholinergic inputs is selectively enhanced during attentional performance. This review aims at integrating the neurophysiological and behavioral evidence on the functions of cortical cholinergic inputs and hypothesizes that the cortical cholinergic input system generally acts to optimize the processing of signals in attention-demanding contexts. Such signals 'recruit', via activation of basal forebrain corticopetal cholinergic projections, the cortical attention systems and thereby amplify the processing of attention-demanding signals (termed 'signal-driven cholinergic modulation of detection'). The activity of corticopetal cholinergic projections is also modulated by direct prefrontal projections to the basal forebrain and, indirectly, to cholinergic terminals elsewhere in the cortex; thus, cortical cholinergic inputs are also involved in the mediation of top-down effects, such as the knowledge-based augmentation of detection (see Footnote 1) of signals and the filtering of irrelevant information (termed 'cognitive cholinergic modulation of detection'). Thus, depending on the quality of signals and task characteristics, cortical cholinergic activity reflects the combined effects of signal-driven and cognitive modulation of detection. This hypothesis begins to explain signal intensity or duration-dependent performance in attention tasks, the distinct effects of cortex-wide versus prefrontal cholinergic deafferentation on attention performance, and it generates specific predictions concerning cortical acetylcholine (ACh) release in attention task-performing animals. Finally, the consequences of abnormalities in the regulation of cortical cholinergic inputs for the manifestation of the symptoms of major neuropsychiatric disorders are conceptualized in terms of dysregulation in the signal-driven and cognitive cholinergic modulation of detection processes.

Acetylcholine↗