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We report results of the variation of signal detectability with radiographic film density for Lanex screens and four different x-ray films. We found that maximum signal detectability occurs near (but not precisely at) the maximum slope of the characteristic curve. We interpret our results using a model that includes film gamma quantum noise, film granularity, and an intrinsic observer contrast threshold.
This study tested the validity of applying a signal detection model to Japanese listeners' /r/-/l/ labeling behavior in one-interval identification task, and the hypothesis that Japanese listeners estimate each token's goodness of fit to Japanese /r/ in labeling it as /r/ or /l/. The identification data obtained by manipulating subjects' response criteria fit the signal detection model. The performance in the identification task was highly predictable based on the goodness of fit judgment, indicating that category goodness information contained in /r/ and /l/ is utilized in deriving underlying sensory decision variables. The data, however, also suggested that these variables are not a direct consequence of the goodness of fit judgment. Various implications of the signal detection model in the investigation of Japanese perception of /r/ and /l/ are discussed.
Human performance in the domain of signal detection is analyzed with respect to the formation of streaks. Streakiness was found to be a general property of auditory and visual discrimination in the sense that correct and incorrect responses have a positive sequential dependency. Success tends to follow success and failure tends to follow failure. Level of streakiness was discovered to be a function of the attentional demand required by the discrimination. Discriminations that make the least demand on attentional resources produce the highest level of streakiness. Monte-Carlo simulations of the observed data sequences suggest that streaky performance is a residue of wave-like variations in perceptual and attentional resources.
Signal detection theory is appropriate for analyzing the problem of whether auditory hallucination arises from a sensory or judgmental disorder. In the present study the sensory discrimination ability and decision bias of psychiatric patients with auditory hallucination was investigated by using the visual continuous performance test. Based on signal detection theory the d' (d prime) and the lnbeta value (the natural logarithm of the beta value) were calculated. The d' is indicator of discriminating ability, whereas the lnbeta value is an indicator of decision bias. The psychiatric inpatients with the diagnosis of schizophrenia mainly were divided into 11 patients with auditory hallucinations (AH(+)) and 11 patients without hallucinations (AH(-)). As compared with the AH(-) group, the AH(+) group showed the same d' value and a significantly lower lnbeta value. As compared with the normal control group, the AH(+) group showed a significantly lower d' value and a nearly normal lnbeta value. These results suggest that auditory hallucination is characterized by a cognitive deficit of unreasonably maintaining a relatively risk-taking decision bias in spite of decreased discriminating ability, which opposes the interpretation of Bentall and Slade (1985). The AH(+) group was divided into subgroups with bizarre delusions (BD(+)) and without bizarre delusions (BD(-)). The BD(+) group showed a stronger tendency toward a lower d' value and normal lnbeta value, which the AH(+) group had.
The independent observation model (Macmillan & Creelman, 1991) is fitted to detection-identification data collected under conditions of heavy masking. The model accurately predicts a quantitative relationship between stimulus detection and stimulus identification over a wide range of detection performance. This model can also be used to offer a signal detection interpretation of the common finding of above-chance identification following a missed signal. While our finding is not a new one, the stimuli used in this experiment (redundant three-letter strings) differ slightly from those used in traditional signal detection work. Also, the stimuli were presented very briefly and heavily masked, conditions typical in the study of unconscious perception effects.
Previous experimental examinations of binary categorization decisions have documented robust behavioral regularities that cannot be predicted by signal detection theory (D.M. Green & J.A. Swets, 1966/1988). The present article reviews the known regularities and demonstrates that they can be accounted for by a minimal modification of signal detection theory: the replacement of the "ideal observer" cutoff placement rule with a cutoff reinforcement learning rule. This modification is derived from a cognitive game theoretic analysis (A.E. Roth & I. Erev, 1995). The modified model reproduces all 19 experimental regularities that have been considered. In all cases,it outperforms the original explanations. Some of these previous explanations are based on important concepts such as conservatism, probability matching, and "the gambler's fallacy" that receive new meanings given the current results. Implications for decision-making research and for applications of traditional signal detection theory are discussed.
Animal models of human cognitive processes are essential for studying the neurobiological mechanisms of these processes and for developing therapies for intoxication and neurodegenerative diseases. A discrete-trial signal detection task was developed for assessing sustained attention in rats; a previous study showed that rats perform as predicted from the human sustained attention literature. In this study, we measured the behavior of humans in a task formally homologous to the task for rats, varying two of the three parameters previously shown to affect performance in rats. Signal quality was manipulated by varying the increment in the intensity of a lamp. Trial rate was varied among values of 4, 7, and 10 trials/min. Accuracy of signal detection was quantified by the proportion of correct detections of the signal (P(hit)) and the proportion of false alarms (P(fa), i.e. incorrect responses on non-signal trials). As with rats, P(hit) in humans increased with increasing signal intensity whereas P(fa) did not. Like rats, humans were sensitive to the trial rate, though the change in behavior depended on the sex of the subject. These data show that visual signal detection behavior in rats and humans is controlled similarly by two important parameters, and suggest that this task assesses similar processes of sustained attention in the two species.
The study was designed to disentangle perceptual and attentional components of the dichotic listening right-ear advantage (REA). A total of 120 normal adults (108 right-handers and 12 left-handers) were administered the Halwes Fused Dichotic Words Test (FDWT) under standard conditions, which entail a forced-choice response format and no attention instructions. Two weeks later, the same stimuli were administered in a signal detection format with varied attention instructions (left, right, and equally divided). The standard task yielded the expected REA. The signal detection task yielded an REA for detection of targets that remained invariant across attention conditions. In contrast, ear asymmetry for localisation of targets varied with attention instructions. The REA on the standard task was correlated with the asymmetry of target detection (r = .57) on the signal detection task but not with the asymmetry of localisation or response bias. Ear asymmetry on the standard test seems to reflect an early stage of processing that is not altered by shifts of attention. Volitional shifts of attention influence the localisation of targets, but this component of signal processing is unrelated to the REA obtained on the standard test.
The influences of hypothyroidism on behavioral measures of the taste function in male and female Long-Evans rats were determined. Experimental rats' preferences for and ability to detect NaCl, HCl, sucrose, and quinine sulfate were examined before, during, and after 9 weeks of maintenance on 0.1% propylthiouracil (PTU), an agent that produces marked hypothyroidism, with similar determinations made for control animals. Despite significant decreases in PTU-treated rats' serum triiodothyronine (T3) and thyroxin (T4), there were no changes in sensitivity or responsivity to the target tastants. However, altered preferences for NaCl, HCl, and quinine sulfate were observed for PTU-treated rats; elevated consumption of HCl and quinine sulfate was present at the end of the study when serum T3 and T4 had returned to near-baseline levels. The data confirm observations that PTU-induced hypothyroidism alters rats' taste preference behavior.
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BACKGROUND: With remission now the treatment goal, antidepressant trial duration has increased. However, most patients do not remit and are exposed to prolonged, ineffective treatment. METHODS: Conditional probabilities and signal detection methodology were contrasted in early detection of nonremitters in three comparator, 12-week antidepressant trials conducted in late- or mid-life depression. RESULTS: The mid- and late-life samples did not differ in rates or time-to-onset of remission or accuracy of early identification of nonremission. Using conditional probabilities, there were marked differences in predictive power depending on the remission criterion. With signal detection methods, sensitivity and specificity of early identification were uniform across the differing medication conditions, remission criteria, and the three studies. By week 6, > or = 60% of ultimate nonremitters were identified, while maintaining a false positive rate < or = 20%. CONCLUSIONS: The goals of providing maximal opportunity to achieve remission, while minimizing exposure to ineffective treatment can be satisfied by use of duration adaptive designs (DAD). While use of conditional probabilities has been the traditional method for early detection of nonremitters, this approach is inferior to use of signal detection methods. The findings also contradicted the widely held view that patients with late-life depression require longer treatment duration.
An extension of signal detection theory (SDT) that incorporates mixtures of the underlying distributions is presented. The mixtures can be motivated by the idea that a presentation of a signal shifts the location of an underlying distribution only if the observer is attending to the signal; otherwise, the distribution is not shifted or is only partially shifted. Thus, trials with a signal presentation consist of a mixture of 2 (or more) latent classes of trials. Mixture SDT provides a general theoretical framework that offers a new perspective on a number of findings. For example, mixture SDT offers an alternative to the unequal variance signal detection model; it can also account for nonlinear normal receiver operating characteristic curves, as found in recent research.
Signal detection analysis was used to examine the effects of d-amphetamine and of morphine on auditory discrimination in female rats. The probability of response repetition in the discrete trial two-choice discrimination procedure was used as an additional behavioral measure. d-Amphetamine (0.4-3.2 mg/kg) and morphine (1.88-15.0 mg/kg) decreased the sensitivity measures (A' and SI) but did not consistently affect the response bias measures (B" and RI). The probability of response repetition was increased by d-amphetamine and was not affected by morphine. It is concluded that the response bias measure B", derived from signal detection theory, and the empirical response bias measure RI, do not discriminate between the different ways in which d-amphetamine and morphine affect discriminative responding, under the conditions of this study.
This paper is concerned with aspects of temporal integration and across-frequency integration in signal detection. Previous experiments on the detection of brief broadband signals (clicks) in continuous broadband noise revealed efficient spectral integration. The extent to which this effect is restricted to a critical time window was investigated by manipulating the temporal relations among the signal components in different frequency regions. In a typical experiment, the signal consists of nine brief Gaussian-shaped tone pulses, equally distributed at 1/3-oct intervals, each with a spectral width of about 1/3 oct, and each equally detectable in white noise. In the synchronized condition (i.e. coinciding peaks of the nine Gaussian envelopes), the detection threshold is reached when the levels of the nine individual tone pulses are about 8 dB below their individual threshold levels (efficient spectral integration). When the signal is progressively desynchronized (i.e. noncoinciding peaks of the Gaussian envelopes), detection threshold is found to increase. This suggests that efficient spectral integration in signal detection is confined to a narrow time window, with a typical value of 30 ms. Similar experiments were performed with respect to the efficiency of temporal integration. For constant-duration signals (100 ms), the detection threshold is found to increase when progressively widening signal bandwidth. The data indicate that the efficient temporal integration in signal detection is confined to a narrow frequency window, which, not surprisingly, corresponds to the critical bandwidth.
One measure of the impact of genetic counseling and testing (GCT) is the extent to which it fosters behavioral change that is consistent with mutation status. We describe and illustrate how two different signal detection methods, receiver operating characteristic (ROC) analysis and recursive partitioning, can be used in this context to evaluate the impact of GCT. We analyzed real screening behavior data obtained in the 12 months following GCT for Hereditary Nonpolyposis Colon Cancer (HNPCC) using these two different signal detection approaches. Each approach demonstrated that GCT had an impact on behavioral outcomes, and was effective in fostering behavioral outcomes appropriate to mutation status. The ROC approach demonstrated that GCT was effective because mutation positive and mutation negative individuals could be distinguished on the basis of the number of recommended screening behaviors. The recursive partitioning approach demonstrated that GCT was effective because there were generally high rates of adherence to screening guidelines among subjects. The recursive partitioning technique also identified four subgroups of subjects, each with distinct characteristics, for which tailored interventions could be developed to increase rates of adherence to screening guidelines. Signal detection methods are easily implemented and are useful techniques for evaluating the impact of GCT.
The usefulness of Fourier-based measures of imaging performance has come into question for the evaluation of digital imaging systems. Figures of merit such as detective quantum efficiency (DQE) based on Fourier domain parameters are relevant for linear, shift-invariant systems with stationary noise. However, no digital imaging system is shift invariant, and realistic images do not satisfy the stationarity condition. Our methods for the task-based evaluation of imaging systems, based on signal detectability in the spatial domain, do not require such assumptions. We have computed the performance of ideal and quasi-ideal observers for the task of signal detection in digital radiography. Signal detectability in terms of an observer signal-to-noise-ratio (SNR) has been compared to results obtained from a Monte Carlo simulation of the digital image-acquisition process. The simulation incorporates the effects of random amplification and secondary quantum blur, integration over pixel area, and electronic noise. The observer figures of merit that have been previously shown to bracket human performance directly specify the usefulness of the images for the stated diagnostic task. In addition, the observer figures of merit give a task-dependent measure of imaging system efficiency in terms of the ratio of an output SNR2 to an input SNR2. Thus, the concept of "detective quantum efficiency" reappears in a natural way but based in the spatial domain and not dependent on shift invariance and stationarity assumptions. With respect to the optimum amount of system blur, our simulations indicate that under certain task-dependent conditions, large signals are fairly insensitive to blur in the x-ray transducer, while an optimum blur is found for small signals.
Unlike many traditional performance measures, signal detection indices of sensitivity are free of response biases. Signal detection and traditional indices of performance were obtained from a short-term recall task during distractor and neutral conditions for schizophrenic patients and normal subjects. Items in each condition had been matched previously for difficulty and consistency to determine whether diminished recall during distraction represented a true differential deficit. Results showed similar patterns for both types of indices: normal subjects performed better than patients across both conditions, patients recalled less after presentation of a distractor than during a neutral condition, and normal subjects showed no performance decrement between the two conditions. These findings demonstrated that the differential deficit was due to changes in schizophrenic patients' sensitivity to stimulus items, not response biases.
Identifying subgroups of high-risk individuals can lead to the development of tailored interventions for those subgroups. This study compared two multivariate statistical methods (logistic regression and signal detection) and evaluated their ability to identify subgroups at risk. The methods identified similar risk predictors and had similar predictive accuracy in exploratory and validation samples. However, the 2 methods did not classify individuals into the same subgroups. Within subgroups, logistic regression identified individuals that were homogeneous in outcome but heterogeneous in risk predictors. In contrast, signal detection identified individuals that were homogeneous in both outcome and risk predictors. Because of the ability to identify homogeneous subgroups, signal detection may be more useful than logistic regression for designing distinct tailored interventions for subgroups of high-risk individuals.