Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Signal detection”

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 127 records · Page 7Linked to original sources
PubMed1992

Signal detection in temporally modulated and spectrally shaped maskers.

The first part of this paper presents several experiments on signal detection in temporally modulated noise, yielding a general approach toward the concept of comodulation masking release (CMR). Measurements were made on masked thresholds of both long- and short-duration, narrow-band signals presented in a 100% sinusoidally amplitude-modulated (SAM) noise masker (modulation frequency 32 Hz), as a function of masker bandwidth from 1/3 oct up to 13/3 octs, while the masker band was geometrically centered at signal frequency. With the short-duration signals placed in the valley of the masker, a substantial CMR (i.e., a decrease of masked threshold with increasing masker bandwidth) was found, whereas for the long-duration signals CMR was smaller. Furthermore, investigations were carried out to determine whether CMR changes when the bandwidth of the signals, consisting of bandpass impulse responses, is increased. The data indicate that substantial CMR remains even when all masker bands contain a signal component, thus minimizing across-channel differences. This finding is not in line with current models accounting for the CMR phenomenon. The second part of this paper concerns signal detection in spectrally shaped noise. Also investigated was whether release from masking occurs for the detection of a pure-tone signal at a valley or a peak of a simultaneously presented masking noise with a sinusoidally rippled power spectrum, when this masker was preceded and followed by a second noise (temporal flanking burst) with an identical spectral shape as the on-signal noise. Similar to CMR effects for temporal modulations, the data indicate that coshaping masking release (CSMR) occurs when the signal is placed in a valley of the spectral envelope of the masker, whereas no release from masking is found when the signal is placed at a peak of the spectral envelope of the masker. The implications of these experiments for measures of spectral and temporal resolution are discussed.

Acoustics↗
PubMed1996

Signal detection analyses of repetition blindness.

Three experiments used a signal detection model to demonstrate that repetition blindness (N. Kanwisher, 1987) reflects a reduction in sensitivity (d') for the detection of repeated compared with unrepeated visual targets. In experiment 1, repetition blindness (RB) was found for rapid serial visual presentation (RSVP) letter sequences, whether the visual targets were specified by category membership (vowels) or as 1 of 2 prespecified letters (e.g., A or O). In Experiment 2, RB was found to a similar degree even when the Ist critical item was displayed for twice as long as the other list items, although overall performance was considerably improved. Experiment 3 found RB for displays containing just 2 simultaneously presented letters. These results support Kanwisher's (1987) account of RB as a genuine perceptual effect, and rule out alternative accounts of RB as the result of response bias, output interference, or guessing biases.

Adult↗
PubMed1999

Decision processes in discrimination: fundamental misrepresentations of signal detection theory.

A new approach to studying decision making in discrimination tasks is described that does not depend on the technical assumptions of signal detection theory (e.g., normality of the encoding distributions). In 3 different experiments, results of these new distribution-free tests converge on a single, surprising conclusion: response biases had substantial effects on the encoding distributions but no effect on the decision rule, which was uniformly unbiased in equal and unequal base rate conditions and in symmetric and asymmetric payoff conditions. This seemingly paradoxical result is fundamentally inconsistent with the entire family of signal detection theory models, raising some important questions about the significance of many published results in the human performance literature.

Decision Making↗
PubMed1984

Anxiety, pain experience, and pain report: a signal-detection study.

The effect of experimentally induced anxiety on pain perception was examined using a signal detection discrimination experiment. The experimental condition consisted in unsignalled application of very painful stimuli which substantially raised state anxiety. The discrimination task included the total range of painful stimuli. The results indicated a range-specific effect of anxiety on pain, particularly on increased sensitivity in the upper range of intensities. The importance of testing the effect of anxiety over the whole range of intensities is stressed. That prior work considered only one intensity level may be the main reason why previous signal detection studies about pain and anxiety showed contradictory results.

Adult↗
PubMed1991

Effects of varying stimulus disparity and the reinforcer ratio in concurrent-schedule and signal-detection procedures.

The present study measured the effects of stimulus and reinforcer variations on pigeons' behavior in two different choice procedures. Two intensities of white light were presented as the stimuli on the main key in a switching-key concurrent schedule and as the sample stimuli in a signal-detection procedure. Under both procedures, the scheduled rate of reinforcement was varied across conditions to produce various ratios of obtained reinforcement. These ratios were obtained for seven pairs of light intensities. In the concurrent schedules, the effects of reinforcer-ratio variations were positively correlated with the physical disparity between the two light intensities. In the signal-detection procedure, changes in the reinforcer ratio produced greater effects on performance when stimulus disparity was very low or very high compared to those found at intermediate levels of stimulus disparity. This discrepancy creates a dilemma for existing behavioral models of signal-detection performance.

Animals↗
PubMed2000

Evaluation of new online automated embolic signal detection algorithm, including comparison with panel of international experts.

BACKGROUND AND PURPOSE: The clinical application of Doppler detection of circulating cerebral emboli will depend on a reliable automated system of embolic signal detection; such a system is not currently available. Previous studies have shown that frequency filtering increases the ratio of embolic signal to background signal intensity and that the incorporation of such an approach into an offline automated detection system markedly improved performance. In this study, we evaluated an online version of the system. In a single-center study, we compared its performance with that of a human expert on data from 2 clinical situations, carotid stenosis and the period immediately after carotid endarterectomy. Because the human expert is currently the "gold standard" for embolic signal detection, we also compared the performance of the system with an international panel of human experts in a multicenter study. METHODS: In the single-center evaluation, the performance of the software was tested against that of a human expert on 20 hours of data from 21 patients with carotid stenosis and 18 hours of data from 9 patients that was recorded after carotid endarterectomy. For the multicenter evaluation, a separate 2-hour data set, recorded from 5 patients after carotid endarterectomy, was analyzed by 6 different human experts using the same equipment and by the software. Agreement was assessed by determining the probability of agreement. RESULTS: In the 20 hours of carotid stenosis data, there were 140 embolic signals with an intensity of > or =7 dB. With the software set at a confidence threshold of 60%, a sensitivity of 85.7% and a specificity of 88.9% for detection of embolic signals were obtained. At higher confidence thresholds, a specificity >95% could be obtained, but this was at the expense of a lower sensitivity. In the 18 hours of post-carotid endarterectomy data, there were 411 embolic signals of > or =7-dB intensity. When the same confidence threshold was used, a sensitivity of 95.4% and a specificity of 97.5% were obtained. In the multicenter evaluation, a total of 127 events were recorded as embolic signals by at least 1 center. The total number of embolic signals detected by the 6 different centers was 84, 93, 108, 92, 63, and 78. The software set at a confidence threshold of 60% detected 90 events as embolic signals. The mean probability of agreement, including all human experts and the software, was 0.83, and this was higher than that for 2 human experts and lower than that for 4 human experts. The mean values for the 6 human observers were averaged to give P=0.84, which was similar to that of the software. CONCLUSIONS: By using the frequency specificity of the intensity increase occurring with embolic signals, we have developed an automated detection system with a much improved sensitivity. Its performance was equal to that of some human experts and only slightly below the mean performance of a panel of human experts

Algorithms↗
PubMed2003

An application of signal detection theory with finite mixture distributions to source discrimination.

A mixture extension of signal detection theory is applied to source discrimination. The basic idea of the approach is that only a portion of the sources (say A or B) of items to be discriminated is encoded or attended to during the study period. As a result, in addition to 2 underlying probability distributions associated with the 2 sources, there is a 3rd distribution that represents items for which sources were not attended to. Thus, over trials, the observed response results from a mixture of an attended (A or B) distribution and a nonattended distribution. The situation differs in an interesting way from detection in that, for detection, there is mixing only on signal trials and not on noise trials, whereas for discrimination, there is mixing on both A and B trials. Predictions of the mixture model are examined for data from several recent studies and in a new experiment.

Association Learning↗
PubMed1997

Concentration-time relationships for the effects of inhaled trichloroethylene on signal detection behavior in rats.

The risk from inhaled volatile organic compounds (VOCs) is presently assessed on the basis of lifetime exposure to average concentrations of the vapor. This strategy yields rational predictions of risk if the product of concentration (C) and the duration of exposure (t) yields constant effects on health (Haber's Rule). The validity of this assumption was evaluated by assessing the acute behavioral effects of inhaled trichloroethylene (TCE) vapor at various values of C and t. Adult male Long-Evans rats (n = 11) were trained to perform a signal detection task in which a press on one lever produced food on trials containing a signal (a brief, unpredictable light flash); a press on a second lever produced food on trials lacking a signal. Response time (RT) and indices of sensitivity (SI) and bias (RI) derived from the theory of signal detection were calculated at three times during repeated daily 60-min tests conducted in air containing 0, 400, 800, 1200, 1600, 2000, or 2400 ppm TCE. Behavior remained stable during tests in air. In TCE, SI declined and RT increased as functions of both C and t. RI was not affected by TCE. Effects on SI and RT were not predictable from the C x t product: both endpoints were more affected by C than by t. To quantify the change in the effect of TCE across exposure times, concentration-effect relationships for inhaled TCE on SI and RT were modeled with cubic polynomial functions at each of the three exposure durations. Concentrations of inhaled TCE associated with preselected changes in SI and RT were then estimated for each animal from these functions. Criterion concentrations, SI0.1 and RT100, were defined as the concentration of TCE associated with a 0.1-unit decrease in SI or a 100-msec increase in RT, respectively. Both SI0. 1 and RT100 increased as exposure duration decreased, but did so more slowly than would be predicted by Haber's Rule. This pattern indicates that application of Haber's Rule overestimates the concentration of inhaled TCE associated with changes in signal detection and thus underestimates the risk of behavior change from short-term exposures to TCE. On the other hand, the fact that SI0.1 and RT100 did increase with shorter exposure times indicates that the converse assumption, that the toxicity of inhaled TCE is independent of the duration of exposure, yields an overly conservative estimate of risk.

Administration, Inhalation↗
PubMedDate not supplied

Changes in secreted salivary sodium are sufficient to alter salt taste sensitivity: use of signal detection measures with continuous monitoring of the oral environment.

A signal detection measure of NaCl taste sensitivity was developed with continuous monitoring of the Na+ concentration of the oral environment. Taste sensitivity was reduced when saliva was stimulated by chewing to secrete with elevated Na+ levels. Monitoring of the oral environment for Na+ allowed a computation of physical signal strengths for NaCl and water stimuli; changes in these strengths, brought about by variations in secreted salivary sodium, furnish an explanation for alterations in NaCl taste sensitivity.

Adult↗
PubMed1991

Signal detection and speech perception with level-dependent hearing protectors.

An experiment was conducted to investigate signal detection and speech perception with level-dependent hearing protectors. Twenty normal-hearing young adults participated in the first phase of this program, the ultimate objective of which was an assessment of the effect of hearing loss. For each subject, measurements were made of the detection of one-third octave noise bands centered at 500, 1000, 2000 and 4000 Hz, consonant discrimination, and word recognition. Performance on these tests was evaluated in quiet and in a background of 75 dB SPL cable swager noise, with the ears unoccluded and protected with four different muffs. The devices selected were the E-A-R 9000 and BILSOM 2390 and their conventional level-independent counterparts, the E-A-R 3000 and BILSOM 2315. The results indicated that signal detection in noise generally remained the same or was slightly enhanced when the protectors were worn. For consonant discrimination, there were no differences among the various protectors in quiet, while in noise the wearing of the BILSOM 2390 resulted in a significant decrement in the intelligibility of the initial consonant. For word recognition, the BILSOM 2390 resulted in an advantage in quiet, particularly for sentences with low contextual cues. The reverse effect was true in noise. The results obtained for the E-A-R 9000 were similar to those for the two conventional HPDs.

Acoustics↗
PubMed2002

Effects of nicotine and mecamylamine on choice accuracy in an operant visual signal detection task in female rats.

RATIONALE: During the past decade, central nicotinic systems have been shown in both experimental animals and humans to play an important role in cognitive function. However, the way in which specific aspects of cognitive function are affected by nicotinic systems has remained unclear. In humans, the most pronounced action of nicotine is to improve attention, but in rats, memory improvement is more easily seen. This may be due to differences in methods for assessing attention in rats and humans or to species differences in the roles of nicotinic systems in cognitive function. In the current study, we explored the effects of nicotine and mecamylamine using an operant visual signal detection task designed to model sustained attention processes common to rats and humans. METHODS: Adult female rats ( n=35) were trained to perform the signal detection task to a stable baseline of about 75% accuracy. The rats were then assigned to two subgroups of high and low accuracy based on overall accuracy (hits and correct rejections) at the end of training. All rats were then injected (SC, 10 min before testing) with saline or different doses of nicotine (0.0125, 0.025, 0.05, 0.1, 0.2 and 0.4 mg/kg) or the nicotinic antagonist mecamylamine (1, 2 and 4 mg/kg). RESULTS: A low dose range of nicotine (0.0125, 0.025, and 0.05 mg/kg) caused a dose-related increase in percent correct rejection. This dose range did not affect correct detections of the signal (percent hit). Higher doses of nicotine (0.1, 0.2 and 0.4 mg/kg) did not affect percent correct rejection, but did have a time-dependent effect on percent hit. Early in the session, the higher doses of nicotine reduced percent hit, whereas during the later part of the session higher doses of nicotine increased percent hit. Effects of nicotine did not differ between the high- and low-accuracy rats. Mecamylamine decreased choice accuracy, reducing both percent hit and percent correct rejection. Mecamylamine reduced percent hit in the low-accuracy rats at a lower drug dose than in the high-accuracy rats. CONCLUSIONS: These results support the involvement of nicotinic systems in attention in rats, as has been shown in humans. This rat model of sustained attention may provide a good approach to studying neural mechanisms underlying the effects of nicotinic cholinergic receptors on attention and a means to evaluate the potential of novel nicotinic agonists to counteract attentional dysfunction.

Animals↗
PubMed2001

The practical application of signal detection theory to image quality assessment in x-ray image intensifier-TV fluoroscopy.

This paper applies a published version of signal detection theory to x-ray image intensifier fluoroscopy data and compares the results with more conventional subjective image quality measures. An eight-bit digital framestore was used to acquire temporally contiguous frames of fluoroscopy data from which the modulation transfer function (MTF(u)) and noise power spectrum were established. These parameters were then combined to give detective quantum efficiency (DQE(u)) and used in conjunction with signal detection theory to calculate contrast-detail performance. DQE(u) was found to lie between 0.1 and 0.5 for a range of fluoroscopy systems. Two separate image quality experiments were then performed in order to assess the correspondence between the objective and subjective methods. First, image quality for a given fluoroscopy system was studied as a function of doserate using objective parameters and a standard subjective contrast-detail method. Following this, the two approaches were used to assess three different fluoroscopy units. Agreement between objective and subjective methods was good; doserate changes were modelled correctly while both methods ranked the three systems consistently.

Biophysical Phenomena↗
PubMed2004

Modeling associative recognition: a comparison of two-high-threshold, two-high-threshold signal detection, and mixture distribution models.

A 2-high-threshold signal detection (HTSDT) model, a mixture distribution (SON) model, and 2-high-threshold (HT) models with responses distributed over 1 or several response categories were fit to results of 6 experiments from 2 studies on associative recognition: R. Kelley and J. T. Wixted (2001) and A. P. Yonelinas (1997). HTSDT assumes that associative recognition is based on conscious recollection and familiarity assessment, whereas according to SON and HT, associative information results in a shift of familiarity. The modeling results cast doubt on the prominent role of conscious recollection, and as far as models are valid, parameter estimation suggests 2 processes in associative recognition: a shift in familiarity that is due to associative information and the determination of the source of familiarity of pairs.

Association↗
PubMed2001

Visual search for orientation among heterogeneous distractors: experimental results and implications for signal-detection theory models of search.

Three experiments tested a signal-detection theory (SDT) model of visual search (e.g., as described in J. Palmer, C. T. Ames, & D. T. Lindsey, 1993). In Experiment 1, participants searched for a 0 degrees line among distractors at (a) 30 degrees; (b) 1/3 at 30 degrees, 2/3 at 50 degrees; (c) 1/3 at 30 degrees, 50 degrees, and 70 degrees; and (d) 1/3 at 30 degrees, 2/3 at 70 degrees. The SDT model predicts improved performance in the more heterogeneous conditions, as some distractors are more discriminable from the target. In contrast, in Experiment 1 human performance degraded in the more heterogeneous conditions (c and d). In Experiment 2, sparser displays improved the performance of the SDT model. In Experiment 3, search for theta degrees among homogeneous theta + 20 degrees distractors was compared with search for theta degrees among theta+/-20 degrees distractors. Performance in the latter condition was often worse, relative to performance in the homogeneous condition, than predicted by the SDT model; however, this depended greatly on the identity of the target.

Humans↗
PubMed2002

Rapid detection of herpes simplex virus DNA in genital ulcers by real-time PCR using SYBR green I dye as the detection signal.

We have evaluated a real-time PCR procedure based on the LightCycler technology for rapid detection of herpes simplex virus (HSV) in genital lesions. Two sets of primers, corresponding to the thymidine kinase and DNA polymerase regions, were used for the amplification reactions in separate capillaries containing the SYBR Green I dye as detection signal. In 28 of 118 samples (24%), HSV was isolated by conventional cell culture. All cell culture-positive samples were also positive by real-time PCR. Six additional cell culture-negative samples were positive by PCR with both sets of primers. Total processing time was less than 3 h. Real-time PCR using SYBR Green I as detection signal is a sensitive procedure for the rapid diagnosis of HSV in genital lesions.

Benzothiazoles↗
PubMed1990

Signal detectability in the presence of monotic or dichotic noise bands of equal or unequal levels.

The application of the power-spectrum model of masking to the detectability of a signal masked by dichotic noise was investigated in three experiments. In each experiment, the signal was a 2-kHz sinusoid of 400-msec duration, masked by either one or two 800-Hz wide bands of noise presented singly or in pairs. In Experiment 1, we compared the detectability of a diotic signal masked by dichotic noise with the detectability of a monaural signal masked by each of the noises separately. The spectrum level of the noise was 35 dB SPL. For dichotic presentations, the signal was sent to both ears while pairs of noise bands, one below and one above the signal frequency, were presented together, one band to each ear. Threshold levels with the dichotic stimuli were lower than or equal to the thresholds with either ear's stimulus on its own. Similar dichotic stimuli were used in Experiment 2, except that the signal frequency was nearer to one or the other of the bands of masking noise, and the noise had a spectrum level of 50 dB SPL. In Experiment 3, thresholds were obtained with two sets of symmetrically and asymmetrically placed notched-noise maskers. For one of these sets, the spectrum level of both noise bands was 35 dB SPL; for the other set, interaural intensity differences were introduced in the form of an inequality in the levels of the noise bands on either side of the signal. In one ear, the spectrum level of the lower frequency noise band was 35 dB SPL and the spectrum level of the higher frequency noise band was 25 dB SPL, whereas in the other ear, the allocation of noise level to noise band was reversed. The dichotic thresholds obtained with the unequal noise maskers could be predicted from the shapes of the auditory filters derived with equal noise maskers. The data from all three experiments suggest that threshold signal levels in the presence of interaural differences in masker intensity depend principally on the ear with the higher signal-to-masker ratio at the output of its auditory filter, a finding consistent with the power-spectrum model of masking.

Adult↗
PubMed1978

EEG event-related potentials and signal detection.

The purpose of this study was to determine whether certain previously reported relationships between event-related potentials and measures of signal detection performance occur in vigilance as well as psychophysical settings. In the course of the study, evidence was found which challenges previously proposed psychological correlates of "P300". EEG was recorded while 15 subjects carried out a 40-min signal detection test. CNV was measured between a warning click and the brief offset of a dim light denoting the possible (p = 0.5) occurrence of the signal, a faint tone in the constant background noise. P300 was measured at a point 300 msec following offset of the dim light. As reported previously in psychophysical settings, P300 amplitude was positively related to signal intensity and response confidence, and was larger for correct detections (Hits) than for correct rejections, misses or false alarms. From first to second half of the test both Hits and false alarms fell, response criterion beta rose, and the amplitude of both CNV and P300 fell. The latter negative relationship between beta and P300 contrasted with a positive one when subjects rated their signal reports at three levels of confidence; here the most confident ratings (high beta) were associated with the highest amplitude of P300. CNV reflected individual ability to sustain performance. Results are explained in terms of a two-factor version (Wilkinson, 1976) of the prior state/reactive change hypothesis (Karlin, 1970). It is suggested that time on task constitutes a prior state influence on P300, whereas other variables influence P300 by means of either reactive change or 'real' change in an endogenous P300 component.

Adult↗
PubMed1985

Reality testing and auditory hallucinations: a signal detection analysis.

The hypothesis that hallucinators are deficient in the metacognitive skill of reality testing was tested using the methodology of signal detection theory. In Expt 1 undergraduate subjects scoring high or low on a scale measuring predisposition to hallucination were tested on an auditory signal detection task. High scorers on the scale were found to differ from low scorers on a measure of perceptual bias but not on a measure of sensitivity. In Expt 2 a similar methodology was used with hallucinating and non-hallucinating schizophrenic patients, with similar results. These results support the hypothesis that hallucinators or subjects highly disposed towards hallucination are deficient in reality testing and are therefore prone to identify imaginary events as real.

Adult↗