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PubMed1998

Roles of DctA and DctB in signal detection by the dicarboxylic acid transport system of Rhizobium leguminosarum.

The dctA gene, coding for the dicarboxylate transport protein, has an inducible promoter dependent on activation by the two-component sensor-regulator pair DctB and DctD. LacZ fusion analysis indicates that there is a single promoter for dctB and dctD. The dctA promoter is also induced by nitrogen limitation, an effect that requires DctB-DctD and NtrC. DctB alone is able to detect dicarboxylates in the absence of DctA and initiate transcription via DctD. However, DctA modifies signal detection by DctB such that in the absence of DctA, the ligand specificity of DctB is broader. dctAp also responds to heterologous induction by osmotic stress in the absence of DctA. This effect requires both DctB and DctD. A transposon insertion in the dctA-dctB intergenic region (dctA101) which locks transcription of dctA at a constitutive level independent of DctB-DctD results in improper signalling by DctB-DctD. Strain RU150, which carries this insertion, is defective in nitrogen fixation (Fix-) and grows very poorly on ammonia as a nitrogen source whenever the DctB-DctD signalling circuit is activated by the presence of a dicarboxylate ligand. Mutation of dctB or dctD in strain RU150 reinstates normal growth on dicarboxylates. This suggests that DctD-P improperly regulates a heterologous nitrogen-sensing operon. Increased expression of DctA, either via a plasmid or by chromosomal duplication, restores control of DctB-DctD and allows strain RU150 to grow on ammonia in the presence of a dicarboxylate. Thus, while DctB is a sensor for dicarboxylates in its own right, it is regulated by DctA. The absence of DctA allows DctB and DctD to become promiscuous with regard to signal detection and cross talk with other operons. This indicates that DctA contributes significantly to the signalling specificity of DctB-DctD and attenuates cross talk with other operons.

Bacterial Proteins↗

PubMed1977

Metacontrast as measured under a signal detection model.

Metacontrast is assessed both by percent accuracy and by the dichotomous sensitivity and criterion measures of a signal-detection model in a forced-choice detection task. The results showed a monotonic increase in sensitivity with increasing mask delay, and an abrupt shift of subjects' response criterion at an 80 ms interstimulus interval. The results are discussed in terms of the interpretational advantages of a signal-detection approach to metacontrast investigation.

Humans↗

PubMed1999

Spreadsheet signal detection.

A number of studies in perception, attention, and memory employ signal detection theory (SDT) to assess the accuracy of an observer's detection or discrimination performance. Some of the problems that students have with understanding and using SDT are associated with the calculations needed to obtain SDT parameters and predictions. All of these calculations, plus the simulation of SDT processes, can be performed using a spreadsheet application program, such as Excel or Quattro Pro. This paper offers a short tutorial on how to use a spreadsheet program to increase your students' knowledge and understanding of SDT.

Computer Simulation↗

PubMed1995

A Distributed Signal Detection Theory Model: Implications for the Design of Warnings.

A distributed signal detection theory model is employed to analyze the effectiveness of warnings under different operating conditions. In particular, the following two cases are examined: (a) the warning on a product is always present and (b) the warning on a product is administered selectively. The comparative effects of warning versus no warning are described. It is established that selectivity always increases effectiveness. The implications to optimal warning design of intermittent hazard versus continuous hazard are discussed. Furthermore, a series of experiments is conducted to compare the behavior of human participants with the prescriptive behavior of the normative model. The changes in the behavior of the human participants response to changes in the warning levels are consistent with the predictions of the model. These changes should be taken into consideration in the design of warnings.

design of warnings↗

PubMed2000

Reinforcer control and human signal-detection performance.

Eight humans participated in a two-choice signal-detection task in which stimulus disparity was varied over four levels. Two procedures arranged asymmetrical numbers of reinforcers received for correct left- and right-key responses (the reinforcer ratio). The controlled procedure ensured that the obtained reinforcer ratio remained constant over changes in stimulus disparity, irrespective of subjects' performances. In the uncontrolled procedure, the asymmetrical reinforcer ratio could covary with subjects' performances. The receiver operating characteristic (ROC) patterns obtained from the controlled procedure approximated isobias functions predicted by criterion location measures of bias. The uncontrolled procedure produced variable ROC patterns that were somewhat like the isobias predictions made by likelihood ratio measures of bias; however, the obtained reinforcer ratio became more extreme as discriminability decreased. The obtained pattern of bias was directly related to the obtained reinforcer ratio. This research indicates that criterion location measures seem to be preferable indices of response bias.

Adult↗

PubMed1975

Stimulus persistence in retarded and nonretarded children: a signal detection analysis.

Nine institutionalized EMR and 9 equal-CA nonretarded children were tested on a visual backward masking task. Signal detection analysis was used to separate the sensory and nonsensory aspects of behavior, and the presentation of stimuli was randomized to minimize the formation of effective strategies. Two sets of instructions, strict and lenient, and two stimulus durations, 10 and 30 msec, were used in a repeated measure design. No differences were found between the intelligence groups on interstimulus interval threshold or measures of stimulus sensitivity, criterion placement, and false positive rate. Retarded subjects showed significantly greater intersubject variability in criterion placement but failed to raise their criterion in response to strict instructions. The results suggest that (a) stimulus-trace concepts of retardation have been confounded by retarded subjects' inability to compete effectively with nonretarded subjects in the experimental situation, and (b) signal detection procedures are a useful alternative to traditional psychophysical techniques in such comparative research.

Adolescent↗

PubMed1979

Signal detection theory and the effects of severe head injury upon recognition memory.

Previous reports by Brooks (1974a, 1974b) employed the techniques of signal detection theory to analyse the effects of severe head injury upon recognition memory. The arguments contained in these papers are criticized with specific reference to the validity of the parameters of signal detection theory as indices of sensitivity and response bias. It is suggested that, when the theory is applied in an appropriate manner, severe head injury is shown to produce an impairment of recognition sensitivity with no concurrent change in response bias. The use of theory neutral procedures for evaluating sensitivity and response bias leads to the same conclusion.

Auditory Perception↗

PubMed1991

Neuroleptics improve sustained attention in schizophrenia. A study using signal detection theory.

To test the hypothesis that antipsychotic drugs improve attentional processes in schizophrenia, we used a computer-controlled, perceptually degraded continuous performance test (CPT), based on signal detection theory. CPT stimuli were degraded (blurred) to reduce discriminability so that signal detection analysis could be used to distinguish specific attentional processes, as measured by A', from nonspecific factors, as measured by B". Thirteen medicated and 12 neuroleptic-withdrawn schizophrenics visually monitored digits to detect a target under perceptually undegraded and degraded conditions. The principal result was that the neuroleptic-withdrawn patients showed a significant decline in the attention-specific measure of A' over time on task only for the degraded targets, independent of changes in the nonspecific index of B". These results demonstrate that neuroleptic withdrawal may compromise specific attentional processes, namely the ability to sustain attention, as measured by a precise performance task which controlled for nonspecific factors.

Adult↗

PubMed2001

Evaluation of a 1 MHz transducer for transcranial Doppler ultrasound including embolic signal detection.

A 1 MHz transducer for use with transcranial Doppler ultrasound may improve the intensity and therefore the detection of embolic signals (ES) and may also reduce the number of absent acoustic windows. A series of studies was performed to investigate its potential benefits. Firstly, ES were detected using a 1 MHz and a 2 MHz transducer both in vitro and in vivo. Secondly, the time taken to identify 100 middle cerebral arteries (MCA) was recorded for both transducers and the best Doppler signal obtained was reviewed off-line and graded for quality. ES were more intense when detected with the 1 MHz compared with the 2 MHz transducer, both in vitro (p <.0001) and in vivo (p <.0001). Of the 100 MCAs studied, 81 had acoustic windows identified with both transducers. The number of acoustic windows detected with one transducer but not the other was the same for both transducers (n = 3). The time taken to identify the MCA was longer with the 1 MHz transducer (p <.0001) and the quality of the signal achieved was poorer (p <.0001). In conclusion, the 1 MHz transducer improved embolic signal intensity but the overall quality of the flow spectrum obtained was poorer with the 1 MHz than with the 2 MHz transducer. A lower frequency transducer of 1 MHz or possibly 1.5 MHz with transcranial Doppler ultrasound may improve the application of embolic signal detection but may not improve the signal for routine measurement of flow velocities.

Endarterectomy, Carotid↗

PubMed2002

A data mining approach for signal detection and analysis.

The WHO database contains over 2.5 million case reports, analysis of this data set is performed with the intention of signal detection. This paper presents an overview of the quantitative method used to highlight dependencies in this data set. The method Bayesian confidence propagation neural network (BCPNN) is used to highlight dependencies in the data set. The method uses Bayesian statistics implemented in a neural network architecture to analyse all reported drug adverse reaction combinations. This method is now in routine use for drug adverse reaction signal detection. Also this approach has been extended to highlight drug group effects and look for higher order dependencies in the WHO data. Quantitatively unexpectedly strong relationships in the data are highlighted relative to general reporting of suspected adverse effects; these associations are then clinically assessed.

Adverse Drug Reaction Reporting Systems↗

PubMed1990

Using signal detection methodology to revise DSM-III-R: re-analysis of the DSM-III-R national field trials for autistic disorder.

Signal detection theory which takes into account the relative prevalence, sensitivity, and specificity of each of a set of criterion symptoms is used to determine an algorithm optimally predictive of a clinical diagnoses of autistic disorder using the data from the DSM-III-R national field trials. Findings support inclusion of one diagnostic criterion (marked lack of awareness of others) as mandatory, and four more (impaired imitation, abnormal social play, abnormal nonverbal communication, and abnormal speech) as alternate, associated criteria. Advantages of signal detection over other statistical methods for empirically deriving diagnostic standards are given, and implications for DSM-IV are discussed.

Algorithms↗

PubMedDate not supplied

The optimization of signal detectability in digital fluoroscopy.

An optimization analysis of digital fluoroscopy has been carried out using (signal/noise)2/dose as a figure of merit. Three signal detection tasks have been considered: (i) small iodine-containing blood vessels; (ii) regions of fat; and (iii) microcalcifications. The effects of x-ray beam filtration and kilovoltage on the figure of merit have been parameterized and the associated x-ray tube power loadings have been defined. Results are presented in a fashion that facilitates the choice of parameters (amount of aluminum filtration, kilovoltage, and x-ray tube power loading) such that an acceptable balance can be achieved between signal detection sensitivity, patient dose, and x-ray tube power loading.

Adipose Tissue↗

PubMed2005

Construct validity of an operant signal detection task for rats.

Many psychoactive drugs produce simultaneous effects on a variety of psychological processes. Behavioral measures in tasks designed to assess cognitive processes in rodents should be able to characterize and dissociate these multiple influences. The present study evaluated how error measures in a classic two-choice operant spatial signal detection paradigm were affected by procedural manipulations of the motivational state of the rat, stimulus properties, and alterations of the inter-trial interval. The experiments were conducted in a two lever operant chamber in which a cue lamp was mounted over each lever. The rats were trained to respond quickly to a short illumination of one of the cue lamps at one of three durations (100, 300 or 1000 ms), presented in a random order. The procedural manipulations were (1) to allow pre-session water access to the normally water-restricted subjects, (2) to vary the intertrial interval (ITI) between sessions, (3) to reduce the intensity of the discriminative stimuli, and (4) to manipulate the variability of the ITI within a session. Stimulus duration-dependent decreases of detection accuracy were observed following pre-session water access and when the intertrial interval was decreased. A reduction of stimulus intensity resulted in decreased accuracy at all stimulus durations. Varying the ITI within the session produced stimulus duration-independent alterations of detection accuracy but no change in the frequency of errors of omission. These findings show that distinct patterns of performance deficits result from manipulating different components of this task and that errors of omission and commission often co-vary and raise questions about the definitions of vigilance and sustained attention as these constructs apply to signal detection tasks that present spatially distinct stimuli.

Animals↗

PubMed2000

Fuzzy signal detection theory: basic postulates and formulas for analyzing human and machine performance.

Signal detection theory (SDT) assumes a division of objective truths or "states of the world" into the nonoverlapping categories of signal and noise. The definition of a signal in many real settings, however, varies with context and over time. In the terminology of fuzzy logic, a real-world signal has a value that falls in a range between unequivocal presence and unequivocal absence. The definition of a response can also be nonbinary. Accordingly the methods of fuzzy logic can be combined with SDT, yielding fuzzy SDT. We describe the basic postulates of fuzzy SDT and provide formulas for fuzzy analysis of detection performance, based on four steps: (a) selection of mapping functions for signal and response; (b) use of mixed-implication functions to assign degrees of membership in hits, false alarms, misses, and correct rejections; (c) computation of fuzzy hit, false alarm, miss, and correct rejection rates; and (d) computation of fuzzy sensitivity and bias measures. Fuzzy SDT can considerably extend the range and utility of SDT by handling the contextual and temporal variability of most real-world signals. Actual or potential applications of fuzzy SDT include evaluation of the performance of human, machine, and human-machine detectors in real systems.

Fuzzy Logic↗

PubMed2005

Eyewitness decisions in simultaneous and sequential lineups: a dual-process signal detection theory analysis.

Many eyewitness researchers have argued for the application of a sequential alternative to the traditional simultaneous lineup, given its role in decreasing false identifications of innocent suspects (sequential superiority effect). However, Ebbesen and Flowe (2002) have recently noted that sequential lineups may merely bring about a shift in response criterion, having no effect on discrimination accuracy. We explored this claim, using a method that allows signal detection theory measures to be collected from eyewitnesses. In three experiments, lineup type was factorially combined with conditions expected to influence response criterion and/or discrimination accuracy. Results were consistent with signal detection theory predictions, including that of a conservative criterion shift with the sequential presentation of lineups. In a fourth experiment, we explored the phenomenological basis for the criterion shift, using the remember-know-guess procedure. In accord with previous research, the criterion shift in sequential lineups was associated with a reduction in familiarity-based responding. It is proposed that the relative similarity between lineup members may create a context in which fluency-based processing is facilitated to a greater extent when lineup members are presented simultaneously.

Adult↗

PubMedDate not supplied

The assessment of intramuscular discrimination using signal detection theory: its potential contribution to chiropractic.

INTRODUCTION: Most studies on sensory changes after manual therapies have focused on pain sensitivity. This ignores the wider range of sensory alternations that may be important in assessing patient functioning and neglects the issue of bias, which is inherent in most methods of pain assessment employing threshold methodology. Signal detection theory (SDT) addresses the issue of bias and provides a measurement of intramuscular discrimination--the ability to discriminate between two stimuli--which can be assessed over the full range of sensation. This paper will discuss the strengths and limitations of SDT and report on the effects of trigger point therapy and manipulation on intramuscular discrimination to illustrate the potential contribution of this methodology to chiropractic. METHODS: Intramuscular needle electrodes were used to provide a pair of electrical stimuli to the forearm extensor muscles. Subjects were asked to assess the differences between stimuli before and after treatment. The treatments consisted of manual trigger point therapy applied to the forearm extensors, cervical spine manipulation and a control treatment. RESULTS: After the trigger point therapy, there was a significant improvement in the ability of the subjects to discriminate between intramuscular signals to treated muscle. Some individual subjects showed alterations in ability to discriminate after cervical spine manipulation but the effect was not significant in the group as a whole. CONCLUSIONS: The methodology of signal detection theory provides a promising, bias-free method of assessing changes in intramuscular sensation after various treatments. In these experiments, trigger point therapy was found to enhance intramuscular discrimination, suggesting that a peripheral reflex may be involved.

Adolescent↗

PubMedDate not supplied

Comparing cognitive and screening tests for neurotoxicity. Effects of acute chlorpyrifos on visual signal detection and a neurobehavioral test battery in rats.

It is often assumed that cognitive function is more sensitive to neurotoxic chemicals than are the unconditioned behaviors employed in neurobehavioral screens; however, direct comparisons of the sensitivity of these test methods are lacking. The present studies were conducted to compare the effects of the widely used cholinesterase-inhibiting insecticide, chlorpyrifos (O,O'-diethyl O-3,5,6-trichloro-2-pyridyl phosphorothionate, CPF), on a visual signal detection task (SDT) with its effects on a neurobehavioral test battery. Adult male Long-Evans rats were trained to perform the SDT, dosed with CPF, and then assessed with both test instruments. Oral CPF (50 mg/kg) impaired signal detection for 8 days, and subcutaneous CPF (250 mg/kg) did so for 4 weeks. CPF (30 and 50 mg/kg po and 250 mg/kg sc) also lowered activity in the test battery for up to 18 days. Thus, CPF impaired attention and altered behavior in the test battery in the same dose ranges under two very different dosing scenarios.

Acetylcholinesterase↗

PubMed1989

Signal detection analysis of ethanol effects on a complex conditional discrimination.

The effects of ethanol on a conditional object identification task were investigated using an operant analog of Signal Detection Analysis. Water and three doses of ethanol (0.40, 0.75 and 1.5 g/kg) were orally administered on three separate occasions to three adult squirrel monkeys. Significant discrimination impairment as a function of increasing ethanol dose was observed. At the 1.5 g/kg dose, impairment extended to nonspecific effects, with subjects ceasing to respond early into the session. Subsequent signal detection analyses revealed that the reduction in performance resulted from losses in discriminability. Response bias was found to change unpredictably and independently of ethanol administration. Reaction time measures also showed no changes except a moderate, nonsignificant, facilitation in speed at the lowest (0.40 g/kg) dose. Taken together, these data suggest that ethanol acts to impair complex, or cognitive, performance by disrupting current sources of stimulus control within the range of doses tested.

Animals↗