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PubMed2005

Impact analysis of signals detected from spontaneous adverse drug reaction reporting data.

This paper describes a new method of prioritising signals of potential adverse drug reactions (ADRs) detected from spontaneous reports that is called impact analysis. This is an interim step between signal detection and detailed signal evaluation. Using mathematical screening tools, large numbers of signals may now be detected from spontaneous ADR databases. Regulatory authorities need to rapidly prioritise them and focus on those that are most likely to require significant action. Using two scores ranging from one to 100, each with three input variables, signals may be categorised in terms of the strength of evidence (E) and the potential public health impact (P). In a two-by-two figure with empirically derived cut-off points of ten (the logarithmic mean) for each score, signals are placed in one of four categories (A-D) that are ranked according to their priority (A being the highest and D the lowest). A sensitivity analysis is then performed that tests the robustness of the categorisation in relation to each of the six input variables. A computer program has been written to facilitate the process and reduce error. Further work is required to test the feasibility and value of impact analysis in practice.

Adverse Drug Reaction Reporting Systems↗
PubMed1994

Signal detection theory and reconstruction algorithms--performance for images in noise.

In many noisy image processing situations, decision making is the ultimate objective. In this paper, we show using signal detection theory how direct optimal processing of the projection data yields a considerable gain in the decision making performance over that obtained by first using image reconstruction. The problem is formulated in the framework of a two hypotheses detection problem. Optimal processors based on the likelihood ratio approach have been presented for two cases. The first considers direct processing of the projection data. The second applies optimal decision theory to the reconstructed data. Results based on computer simulation are presented in the form of receiver operating curves (ROCs) for different signal-to-noise (SNR) ratios. Early results indicate that large performance gains can be achieved by direct optimal processing of the projection data compared with optimal processing of reconstructed data. Results for the latter case can be interpreted as providing an upper bound on all postreconstruction decision rules. We hope to extend this approach to a number of different aspects of the image decision making problem.

Algorithms↗
PubMed1984

Perception of voice-onset-time continua: a signal detection analysis.

An absolute identification task and various discrimination tasks were performed on synthetic syllables initiated by alveolar stops varying in voice-onset-time (VOT). Signal detection analyses of the data yielded three main findings. First, discrimination d's exceeded those for absolute identification. Greater instability of judgment in the latter than in the former task explained this difference. Second, stimuli within a phonetic category were discriminable, even in a delayed 2IAX paradigm with 4s between stimuli. Third, a category boundary effect appeared: identification and discrimination d's were largest around the voiced/voiceless boundary for alveolar stops. The relationship between discrimination and identification d's varies with response constraints, the number of just noticeable differences in the stimulus array, and stability of judgments in the various tasks. Nearly equal performance in discrimination and identification tasks is not a sufficient condition for a category boundary effect to occur. Several arguments are advanced against a dual-coding model. A continuous model which invokes only a single decision process may account more gracefully for the relationship between identification and discrimination of both consonants and vowels.

Humans↗
PubMed1980

Signal detection analysis of visual flicker in deaf and hearing individuals.

A comparison of deaf and hearing subjects on temporal visual resolving power was conducted within a signal-detection paradigm. Subjects were required to make forced-choice judgments of a visual-flicker task under three stimulus probability conditions (0.25, 0.50, 0.75). A total of 600 trials were given each subject from which d' and Beta, indices for sensory sensitivity and response bias respectively, were computed. No significant differences existed on sensory sensitivity or response bias which questions some traditional assumptions about sensory compensation.

Adolescent↗
PubMed1981

Semantic comprehension in infancy: a signal detection analysis.

The purpose of this study was to validate a paradigm by which an infant's comprehension of concrete nouns could be assessed while controlling for (a) response bias, (b) stimulus preference, and (c) maternal cuing. More specifically, we sought to determine whether 11- and 13-month-old infants directed their eye fixations to the referent of an object word said by the mother and to determine whether there was a developmental shift in responding to object words at these 2 ages, as some previous research suggests. Duration of looking at each of 4 corners of an apparatus was measured while the mother (unable to see what the child was doing) uttered a word she felt the infant knew, 1 she felt he/she did not know, and a nonsense word. Analyses based on signal detection theory using "known" words as signal trials and nonsense words as noise revealed that 13-month-olds directed their looking time significantly longer at the referent of the known word when that word was uttered than when the nonsense word was uttered. At neither age did looking at the referent of the unknown word exceed control values. No significant effects were obtained at 11 months of age, nor were there any sex effects.

Discrimination Learning↗
PubMed1982

The accuracy of eye-gaze judgment: a signal detection approach.

Two studies are reported which tested the hypothesis that eye-gaze discriminability declines with increased interpersonal distance and that this decline produces an overestimation bias. Signal detection theory was used to provide separate indices of discriminability and bias. Discriminability declined with both increased distance and, in one study, with decreased lighting. The tendency of the subject to guess that gaze was occurring when it was not mirrored the changes in discriminability, supporting the hypothesis.

Adult↗
PubMed1982

Two-point tactual discrimination on the back: a signal-detection approach.

This investigation determined if subthreshold two-point aesthesiometer separations could be discriminated from one-point on the back, using a fixed-based matching signal detection technique. Subjects reliably discriminated two-point separations as small as 2 mm from one point on the back. In addition, the back appears to be more sensitive to discriminating two points from one point than the dorsal forearm.

Back↗
PubMed1997

A signal detection theory analysis of gap detection in the rat.

An innocuous sensory event (a prestimulus) briefly preceding a startle-eliciting stimulus (SES) reduces the amplitude of the elicited reflex. This study used signal detection theory (SDT) techniques to quantify the effects of gaps (pauses in otherwise continuous noise) on the rat's acoustic startle reflex. Sixteen rats were given four identical test sessions consisting of the randomized presentation of 150 trials of the SES alone and 150 trials of a gap-and-SES combination. Gap duration (1, 2, 4, and 8 msec) varied between sessions. Data analyses based on amplitude, difference scores, percentage scores, and SDT techniques identified similar patterns. The three longest gaps, but not the shortest, were reliably detected, and differences among these three were identified with percentage and SDT analyses. Analyses of amplitude changes over test sessions yielded different patterns for each measure. The results demonstrate that an SDT analysis is a sensitive index of prestimulus effects.

Animals↗
PubMed1975

Decision-related cortical potentials during an auditory signal detection task with cued observation intervals.

Cortical-evoked potentials were recorded from human subjects performing an auditory detection task with confidence rating responses. Unlike earlier studies that used similar procedures, the observation interval during which the auditory signal could occur was clearly marked by a visual cue light. By precisely defining the observation interval and, hence, syncrhonizing all perceptual decisions to the evoked potential averaging epoch, it was possible to demonstrate that high-confidence false alarms for accompanied by late-positive P3 components equivalent to those for equally confident hits. Moreover the hit and false alarm evoked potentials were found to covary similarily with variations in confidence rating and to have similar amplitude distributions over the scalp. In a second experiment wherein the signal intensity was increased to make signal presence and signal absence clearly discriminable and the a priori probability of signal presentation was varied from .5 to .9, it was demonstrated that correct rejections can be associated with a P3 component larger than that for hits. Thus it was possible to show, within the signal detection paradigm, how the two major factors of decision confidence and expectancy are reflected in the P3 component of the cortical-evoked potential.

Adult↗
PubMed1979

Signal detection in computer-synthesized noise.

Human observers detected sinusoidal and pulse-train signals in noise derived from two computer-synthesized sources and from a Gaussian noise source. The synthesized noise stimuli were generated from sequences of pulses whose amplitudes were drawn from two divergent types of probability distributions: a centrally peaked distribution and a bimodal distribution. No differences in the detectability of signals in these noise stimuli were evident at pulse rates of 1000, 2000, 4000, or 10 000 Hz. subjects could not discriminate between the two types of computer-generated maskers at any pulse rate. The data support a spectrum-analyzer model of detection in which multiband filtering of the input smooths the masker energy in each spectral region to approximate the Gaussian case.

Computers↗
PubMed1981

The effects of induced anxiety on pain perception: a signal detection analysis.

This investigation assessed the effects of induced anxiety on pain perception. Anxiety was documented by self-report verbal indices and physiological indices. Measurement procedures bases on signal detection theory were employed to separate discriminability and response bias in reporting pain. The major finding of the study was that induced anxiety, as defined by the combination of physiological and verbal indices, decreases pain sensitivity and the tendency to report sensations as painful. However, induced anxiety as defined by less stringent criteria (i.e., physiological or verbal indices alone), decreased discriminability, but not response bias, and the decrease was less than in patients who were defined as anxious by the more comprehensive criteria. The importance of documenting anxiety independently of the experimental manipulation and the value of using pain stimuli producing sensations similar to clinical pain is discussed.

Anxiety↗
PubMed1973

Analgesic strength of 33 percent nitrous oxide: a signal detection theory evaluation.

Radiant heat stimulation was applied to volunteers and rating scale responses were obtained to assess the analgesic properties of 33 percent nitrous oxide. The methodology of signal detection theory was applied to the data to demonstrate that nitrous oxide reduces both sensitivity to pain and willingness to report pain. This method is superior to threshold estimation for the evaluation of analgesics.

Adult↗
PubMed1981

Two-point tactual discrimination: a signal detection approach.

This investigation determined if subthreshold two-point aesthesiometer separations could be discriminated from one-point on the dorsal forearm. A fixed-based matching signal-detection technique was employed. The results indicated that subjects can reliably discriminate two-point separations as small as 2 mm when compared to one point.

Discrimination Learning↗
PubMed1992

Continuous recognition memory tests: are the assumptions of the theory of signal detection met?

Two continuous recognition memory tests were administered to 20 males and 20 females using the confidence rating procedure to determine if the underlying assumptions of the theory of signal detection (TSD) are met by these tasks. Z-score transformed ROC curves proved to be straight lines parallel to the positive diagonal of the ROC graph. These findings suggest that the distributions of familiarity for old and new stimuli are normal and of equal variance for the Continuous Recognition Memory and Continuous Visual Memory Tests. TSD interpretation of test data appears to be justified.

Adolescent↗
PubMed1997

Lipid signals detected by NMR proton spectroscopy of whole cells are not correlated to lipid droplets evidenced by the Nile red staining.

Nile red staining was used to detect lipid droplets in the K562 cell line sensitive and resistant to adriamycin and their resistance-reversing counterparts. The staining obtained was compared to the intensity of lipid signal detected in proton nuclear magnetic resonance spectra. From the four cell lines used, a lack of correlation was observed between the NMR signal and the Nile red staining. For example, the sensitive K562 cells, with the highest level of NMR signals, showed only few cells containing lipid droplets. We concluded that is lipid droplets can participate to lipid signal in NMR spectra, other lipids must also participate to these resonance.

Doxorubicin↗
PubMed1979

Methadone depression of visual signal detection performance.

In order to determine the origin of a previously reported slowing of simple visual reaction time in subjects receiving single doses of oral methadone, three well-trained subjects performed. a modified double flash detection task several times after single doses of 5 mg and 10 mg of oral methadone and a placebo. A Theory of Signal Detectability analysis allowed for a clear distinction between drug-induced changes in visual sensitivity and changes in response bias. It was found that methadone reduced visual sensitivity. The peak depression in detection as well as the duration of the depressed performance were dose-related. Depression in performance paralleled the subjective effect of the drug in each subject. Averaged visual evoked potentials showed significant changes at peak drug effect to the onset of each of the pair of stimuli. It was concluded that methadone depresses visual function by acting on the visual parts of the central nervous system. The retina, midbrain and thalamic visual nuclei were discussed as possible sites of action of methadone.

Adult↗
PubMed2001

Signal detection in amplitude-modulated maskers. II. Processing in the songbird's auditory forebrain.

In the natural environment, acoustic signals have to be detected in ubiquitous background noise. Temporal fluctuations of background noise can be exploited by the auditory system to enhance signal detection, especially if spectral masking components are coherently amplitude modulated across several auditory channels (a phenomenon called 'comodulation masking release'). In this study of neuronal mechanisms of masking release in the primary auditory forebrain (field L) of awake European starlings (Sturnus vulgaris), we determined and compared neural detection thresholds for 20-ms probe tones presented in a background of sinusoidally amplitude modulated (10-Hz) noise maskers. Responses of a total of 34 multiunit clusters were recorded via radiotelemetry with chronically implanted microelectrodes from unrestrained birds. For maskers consisting of a single noise band centred around the recording site's characteristic frequency, a substantial reduction in detection threshold (21 dB on average) was found when probe tones were presented during envelope dips rather than during envelope peaks. Such effects could also explain results obtained for masking protocols where the on-frequency noise band was presented together with excitatory or inhibitory flanking bands that were either coherently modulated (in-phase) or incoherently modulated (phase-shifted). Generally, masking release for probe tones in maskers with flanking bands extending beyond the frequency range of a cell cluster's excitatory tuning curve was not substantially improved. Only some of the neurophysiological results are in agreement with behavioural data from the same species if only the average population response is considered. A subsample of individual neurons, however, could account for behavioural thresholds.

Acoustic Stimulation↗
PubMedDate not supplied

A comparison of measures of disproportionality for signal detection in spontaneous reporting systems for adverse drug reactions.

PURPOSE: A continuous systematic review of all combinations of drugs and suspected adverse reactions (ADRs) reported to a spontaneous reporting system, is necessary to optimize signal detection. To focus attention of human reviewers, quantitative procedures can be used to sift data in different ways. In various centres, different measures are used to quantify the extent to which an ADR is reported disproportionally to a certain drug compared to the generality of the database. The objective of this study is to examine the level of concordance of the various estimates to the measure used by the WHO Collaborating Centre for International ADR monitoring, the information component (IC), when applied to the dataset of the Netherlands Pharmacovigilance Foundation Lareb. METHODS: The Reporting Odds Ratio--1.96 standard errors (SE), proportional reporting ratio--1.96 SE, Yule's Q--1.96 SE, the Poisson probability and Chi-square test of all 17,330 combinations were compared with the IC minus 2 standard deviations. Additionally, the concordance of the various tests, in respect to the number of reports per combination, was examined. RESULTS: In general, sensitivity was high in respect to the reference measure when a combination of point- and precision estimate was used. The concordance increased dramatically when the number of reports per combination increased. CONCLUSION: This study shows that the different measures used are broadly comparable when four or more cases per combination have been collected.

Adverse Drug Reaction Reporting Systems↗