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At least 199 records · Page 11Linked to original sources
PubMed1985

Evaluation of signal detection theory on the effects of psychotropic drugs on critical flicker-fusion frequency in normal subjects.

Critical flicker-fusion frequency (CFF) has often been applied to psychotropic drug evaluation as a measure of cortical arousal. There are several variables that must be considered for proper conclusions to be obtained from CFF experimental data. Psychological variables such as subject response bias are especially difficult to control. We studied the effects of single oral doses of 10 mg diazepam and 10 mg amphetamine sulfate on CFF values obtained by a block up-down spatial forced-choice method on 13 healthy volunteers (seven males and six females). Signal detection theory was also used to obtain the non-parametric value P(A) as a measure of sensory function and B as a measure of the psychological function of response bias. As a group, amphetamine increased CFF (Hz) and P(A) and diazepam decreased CFF (Hz) and P(A), with the most significant effects observed at 2 and 3 h after drug administration. B scores showed more individual variation with a trend towards a low score, or a tendency to report more flicker responses after diazepam. Separated by sex, the males had a higher percentage of subjects that demonstrated a reduction of CFF after diazepam, while the females had a higher percentage that demonstrated an increase in CFF after amphetamine. The results suggest that CFF changes following diazepam and amphetamine are mostly changes in sensory function and not changes in response bias. It is possible to apply signal detection theory to flicker-fusion studies and the accounting of bias by controlling, measuring or eliminating it is essential in interpretation of CFF data.

Amphetamine↗
PubMed2000

EMG signals detection and processing for on-line control of functional electrical stimulation.

The surface EMG signal detected from voluntarily activated muscles can be used as a control signal for functional neuromuscular electrical stimulation. A proper positioning of the recording electrodes in relation to the stimulation electrodes, and a proper processing of the recorded signals is required to reduce the stimulus artefact and the non-voluntary contribution (M-wave). Six orientations and six locations of the recording electrodes were investigated in the present work. A comb filter (with and without a blanking windowing) was applied to remove the signal components synchronously correlated to the stimulus. An operative definition of the signal to noise ratio and an efficiency index were implemented. It resulted that when the recording electrodes were located within the two stimulation electrodes the best orientation was perpendicular to the longitudinal line. However the best absolute indexes were obtained when the recording electrodes were located externally of the stimulation electrodes, and in that case the best orientation was longitudinal. Concerning the filtering procedure, the use of a blanking window before the application of the comb filter, gave the best performance.

Artifacts↗
PubMed1991

Listening bandwidths and frequency uncertainty in pure-tone signal detection.

The effect of frequency uncertainty on the detection of tonal signals in noise was studied using a modified probe-signal method. Widths of the listening bands used during detection were measured directly, allowing for an analysis that separates the effects of having to monitor multiple independent bands from those due to limited frequency resolution. Uncertainty was varied by beginning each trial with a cue consisting of one, two, or four randomly chosen, simultaneously presented tones. An expected signal, whose frequency matched one of the components in a cue, was presented on a majority of trials. However, on remaining trials, the signal was a probe, which meant that its frequency differed from one of the components in the cue by a constant ratio. Performance as measured in percent correct declined for probes at increasingly distant ratios from the expected values. The results were converted to dB using individual psychometric functions for expected signals and listening bands were fitted using the rounded exponential filter of Patterson et al. [J. Acoust. Soc. Am. 72, 1788-1803 (1982)]. The obtained bandwidths are comparable to those reported using notched-noise maskers, but there is a small but consistent increase in bandwidth with increased numbers of components in the cues. The primary results is that the effects due to uncertainty are well described by a 1-of-M orthogonal band model, which takes into consideration limitations of the detector, including the widths of the listening bands.

Attention↗
PubMed2003

Application of automated mRNA in situ hybridization for formalin-fixed, paraffin-embedded mouse skin sections: effects of heat and enzyme pretreatment on mRNA signal detection.

Recently, an automated mRNA in situ hybridization application was introduced for the Ventana Discovery instrument. The application was designed so that all necessary steps from baking through signal detection were completed within 1 day on the instrument. We applied this technology for visualizing the expression site of versican in formalin-fixed mouse skin paraffin tissue sections. Our focus of this study was to demonstrate the effects of protease digestion or heating pretreatment, termed cell conditioning, on the hybridization signal using a well characterized versican antisense riboprobe. Paraffin sections were automatically deparaffinized, fixed, and acid-treated. Then, the tissue sections were subjected to protease digestion alone (3 strengths), cell conditioning alone, or the combination of cell conditioning and protease digestion. Hybridization was performed with digoxigenin-labeled versican antisense probe (20 ng/slide) for 6 hours, and the signal was detected using a Nitro blue Tetrazolium chloride 5-Bromo-4-cloro-3-indolyl phosphate toluidine salt (NBT/BCLIP) substrate solution for 3 hours on the instrument. Cell conditioning alone did not produce any signal, whereas the highest strength of protease digestion produced noticeable background staining. However, when cell conditioning and mild protease digestion were combined, the signal for versican mRNA was clearly demonstrated in the hair papilla region. Thus, we demonstrated the effects of the cell conditioning step followed by mild protease digestion for enhancing the mRNA target staining compared with protease digestion or the cell conditioning step alone. We verified that the automated in situ hybridization process was applicable for formalin-fixed mouse skin paraffin sections and that the automated 1-day protocol is simple and reproducible. The precise control of automation allows fine tuning of temperature and enzyme dose to find the optimized assay condition for the signal to noise ratio and morphology.

Animals↗
PubMed2001

Signal-detection analysis of group decision making.

How effectively can groups of people make yes-or-no decisions? To answer this question, we used signal-detection theory to model the behavior of groups of human participants in a visual detection task. The detection model specifies how performance depends on the group's size, the competence of the members, the correlation among members' judgments, the constraints on member interaction, and the group's decision rule. The model also allows specification of performance efficiency, which is a measure of how closely a group's performance matches the statistically optimal group. The performance of our groups was consistent with the theoretical predictions, but efficiency decreased as group size increased. This result was attributable to a decrease in the effort that members gave to their individual tasks rather than to an inefficiency in combining the information in the members' judgments.

Decision Making↗
PubMed2000

A signal detection model predicts the effects of set size on visual search accuracy for feature, conjunction, triple conjunction, and disjunction displays.

Recently, quantitative models based on signal detection theory have been successfully applied to the prediction of human accuracy in visual search for a target that differs from distractors along a single attribute (feature search). The present paper extends these models for visual search accuracy to multidimensional search displays in which the target differs from the distractors along more than one feature dimension (conjunction, disjunction, and triple conjunction displays). The model assumes that each element in the display elicits a noisy representation for each of the relevant feature dimensions. The observer combines the representations across feature dimensions to obtain a single decision variable, and the stimulus with the maximum value determines the response. The model accurately predicts human experimental data on visual search accuracy in conjunctions and disjunctions of contrast and orientation. The model accounts for performance degradation without resorting to a limited-capacity spatially localized and temporally serial mechanism by which to bind information across feature dimensions.

Adult↗
PubMed2001

Resonance-enhanced signal detection and transduction in the Hodgkin-Huxley neuronal systems.

The ability of signal detection and transduction of the Hodgkin-Huxley neuronal systems, associated with rhythmic oscillations in the presence of external modulations, is studied. Both inhibitory and excitatory modulations, regarded as the total effects of the environment in which the neurons are located, are able to modulate the frequencies of the rhythmic oscillations of the neurons. Either subthreshold or suprathreshold rhythmic oscillations can provide the neural system with an effect of frequency selection in processing external signal. Resonance among the noise, the noise-induced oscillation, and the signal enhances intensively the capability of the neurons in processing the weak signal, especially when frequency of the signal is around that of the noise-induced rhythmic oscillation. Thus, the neuronal system can be adjusted to an optimal sensitive state for signal processing through the environmental modulations.

Action Potentials↗
PubMedDate not supplied

Signal detection indices in schizophrenics on a visual, auditory, and bimodal Continuous Performance Test.

Signal detection indices (perceptual sensitivity) were calculated to compare performance of 24 male schizophrenic inpatients and 24 controls (12 alcoholics and 12 normals) on 4 different CPT-tests. A standard version (St) employed 1 target (P = 0.166) and 5 nontargets. In condition V stimuli were presented visually, in condition A acoustically and in condition VA bimodally (1 target (P = 0.333) and 1 nontarget). Compared to controls schizophrenics exhibited lower levels of perceptual sensitivity in all 4 conditions. They were especially impaired when stimuli were presented either acoustically or when they had to monitor 2 modalities simultaneously. Perceptual sensitivity of schizophrenics was significantly lower in conditions V, A, and VA than in condition St. For controls only condition VA led to lower values. Because St was always presented first, the possible explanation that vigilance decrement over time is responsible for the lowered perceptual sensitivity had to be ruled out. It could be shown that schizophrenics did not differ in sensitivity between conditions being later in task sequence. Controls, however, showed a slight decrement over time. Thus our finding should to a large extent be attributed to different task requirements. Response criterion beta yielded inconsistent results.

Adult↗
PubMed2005

Classification images for chromatic signal detection.

The number and nature of the mechanisms for the detection of colored stimuli are still unclear. We use the paradigm of classification images to investigate the detection of a signal of homogeneous color added to a noisy texture. Both signal and noise colors were chosen from the isoluminant plane of the Derrington-Krauskopf-Lennie (DKL) color space. The signal consisted of a square of homogeneous color that was chosen from either cardinal or noncardinal directions of the DKL color space. The noisy texture consisted of small squares of varying colors that were chosen randomly across the isoluminant plane. Classification images reveal that (1) the cardinal axes play no specific role; (2) the widths of the tuning curves vary between 30 and 90 deg, consistent with the variation of tuning widths of neurons at early cortical stages; and (3) detection is not based on the whole region covered by the signal but is influenced mostly by a small spot around the fixation point.

Color Perception↗
PubMed1995

Cuing mechanisms in auditory signal detection.

Detection of auditory signals under frequency uncertainty can be improved by presenting cues to the listeners. Since various cues have been found to differ in effectiveness, three conceivable mechanisms were considered which might account for these differences. Cuing might reduce the number and/or width of the employed auditory filters or listening bands. Also, cues could modulate the precision of frequency tuning of the filters. Psychometric functions were collected in a detection experiment with frequency uncertainty employing three kinds of cues: pure tones whose frequency was identical to that of the signal (iconic cues), complex tones with a missing fundamental equal to the signal (complex cues), and pure tones with a certain frequency relation to the signal (relative cues). Compared with a no-cue condition, all cue types improved detection performance. Fitting models to the data suggests that in the no-cue condition as well as the complex-cue condition, multiple bands were utilized, and that the iconic and relative cues induced single-band listening. There is no indication that accuracy of frequency tuning was responsible for cue-efficiency differences.

Attention↗
PubMed1999

A signal detection analysis of auditory-frequency discrimination in the rat.

The frequency-discrimination behavior of rats in a simple go/no-go task was analyzed using the theory of signal detection. Discrimination acuity was studied and the receiver operating characteristic (ROC) was generated in subjects by varying the reinforcement schedule and signal probability. The detectability indices d', A', and sensitivity index (SI) and response-bias indices B" and responsivity index (RI) were used to describe behavior. A' gave the most suitable psychometric functions while RI best described response-bias behavior. Weber ratios were 6.25% +/- 0.23% at 5 kHz in three subjects. The best method to obtain the ROC was to vary the probability with which subjects were reinforced. The ROC in two subjects demonstrated classical forms; in another subject, the function was asymmetric to the extent that detectability was not independent of response bias. Subjects altered their decision criterion in reporting a signal from trial to trial depending on previous trial events. On any given trial, subjects made a decision in one of several "decision states." Variables that influenced decision states included previous reinforcement and timeouts. The data indicate that timeouts may not be a useful feature in go/no-go tasks. The identification of multiple-decision states within a single behavioral session is a convenient method to generate the ROC without expressly manipulating experimental conditions.

Animals↗
PubMed1995

[MR diagnosis for metastasis or non-metastasis of mediastinal and hilar lymph nodes in cases of primary lung cancer: detectability, signal intensity, and MR-pathologic correlation].

The detectability and signal intensity on MR imaging of mediastinal and hilar lymph nodes were studied in cases of lung cancer. Additionally, short inversion time inversion recovery (STIR) images and pathologic findings were compared. In the detection of resected metastatic mediastinal and hilar lymph nodes (n = 146), the STIR image (82%) was superior to the T1-weighted image (71%) and the T2-weighted image (60%). On STIR imaging, 212 (60%) of 412 resected non-metastatic mediastinal nodes and 38 (33%) of 116 resected non-metastatic hilar lymph nodes were detected. Characteristics of signal intensities of metastatic nodes were mainly low on T1-weighted images, high on T2-weighted images, and very high on STIR images. The rate of these characteristics of signal intensity of metastatic nodes was 59%. However, the rate of very high signal intensity of metastatic nodes on STIR imaging was 81%. Pathologically, lymph nodes with high or very high signal intensities on STIR images were metastatic, reactive and hyperplastic, or non-metastatic. Lymph nodes with slightly high signal intensity or high intensity with a low focus on STIR images were anthracotic, anthrasilicotic, caseous necrotic, calcified, or fibrotic. Thus, when the signal intensity of a lymph node was decreased on the STIR image, there was no definite evidence of metastasis excluding micro-metastasis or coagulation necrosis of a metastatic tumor. We conclude that the signal characteristics on STIR imaging are useful for distinguishing between macro-metastatic and non-metastatic lymph nodes when enlarged nodes are detected by various other types of medical imaging.

Adenocarcinoma↗
PubMed1982

Reinforcement contingencies and signal detection.

Pigeons were trained to discriminate temporal stimuli in a discrete-trial signal-detection procedure. Pecks to one side key were reinforced intermittently after exposure to one duration, and pecks to the other side key were reinforced intermittently after exposure to a different duration. In Experiment I, the allocation of reinforcers was varied systematically for correct responses and for errors, using a procedure that controlled the obtained numbers of reinforcers. When reinforcers were allocated symmetrically, the level of discrimination decreased as the proportion of reinforcers for errors increased. When reinforcers were allocated asymmetrically, the decrease in discrimination was less systematic. Bias toward one or the other side key roughly matched the ratio of reinforcers obtained by pecks at those keys, independent of the level of discrimination. In Experiment II, the overall rate of reinforcement for correct responses was varied both within and between experimental conditions. The level of discrimination was positively related to the overall rate of reinforcement. The discrimination data of both experiments were interpreted in relation to the contingencies of reinforcement and nonreinforcement, characterized by the average difference in reinforcement probability for correct responses and errors.

Animals↗
PubMed1991

Poisson signal-detection theory: link between threshold models and the Gaussian assumption.

The Gaussian model of signal detection cannot fit asymmetric data as long as the variances of the distributions are kept equal. It is therefore common practice to assume unequal variances in order to fit these data. But this assumption leads to the well-known crossover problem. The present paper provides new arguments for the abandonment of the Gaussian model with unequal variances. In its stead, this paper reevaluates multiple-parallel-threshold models. In particular, the Poisson model turns out to be very useful: it can handle data with any degree of asymmetry, giving a reasonable interpretation of the two parameters of the receiver-operating characteristic. The three-state-threshold model (Krantz, 1969) is given a new interpretation in light of the Poisson model. The slope of Poisson double-probability plots turns out to be much closer to unity than is predicted by the Gaussian approximation.

Attention↗
PubMed2003

Receiver operating characteristics in the lexical decision task: evidence for a simple signal-detection process simulated by the multiple read-out model.

This study provides further evidence for the hypothesis that performance in the lexical decision task is based on the output of a signal detection mechanism, as implemented by the multiple read-out model of word recognition (MROM; J. Grainger & A. M. Jacobs, 1996). We extend the MROM to allow predictions of receiver operating characteristics in a data-limited variant of the lexical decision task and show that the model provides accurate descriptions of the data. Our results challenge all models of word recognition that do not include a familiarity assessment mechanism. They also suggest that under data-limited conditions a deadline mechanism for generating "no" responses in the lexical decision task may not necessarily be functional.

Decision Making↗
PubMed1983

The effect of hearing protection on narrowband signal detection in industrial noise.

A method for evaluating the effectiveness of insert protectors at suprathreshold intensities was developed. Normal listeners and workers with clinically diagnosed, bilateral, noise-induced hearing loss attempted to detect a 1 or 3 kHz narrowband signal, 500 msec in duration. The signal was presented binaurally over headphones, either in quiet or against a background of industrial noise taped on site. The level of the noise was fixed at 84 dBA. The level of the signal was varied across blocks of 50 trials from near threshold to clearly audible. Comparisons were made between the detectability of the signal when insert protectors were worn, and listening without protection. The results indicated that in both normal and hearing impaired listeners the slopes of the psychometric functions were fairly steep, covering a range of only about 5 dB. The value of attenuation of the insert protector derived from the displacement of the function for listening in quiet with the protector, relative to listening with the open ear was constant throughout the range of suprathreshold signal intensities used. In 84 dBA of background noise normal subjects showed an improvement of about 3 dB when they wore protectors. By contrast the wearing of protectors in noise by hearing impaired listeners resulted in substantial decrements in signal detection.

Audiometry↗
PubMed2001

Characterisation of human knee-joint proprioception by means of a signal-detection theory.

Human proprioceptive performance of movement detection in joints is currently believed to be based on information from muscle spindles. In previous studies investigating proprioception, we found remarkable differences in threshold values using a conventional movement-detection paradigm and a threshold-hunting paradigm. One reason could be that central processing, the evaluation of the peripheral sensation, was responsible. Therefore, the study was designed to determine, besides the proprioceptive performance, the central processing of movement detection in the knee joint by means of a signal-detection technique (SDT). Only this technique provides parameters such as detectability (d') and the decision criterion (beta), which distinguish between these performances. From the resulting psychometric functions, the threshold (a parameter of classical psychophysics) also was evaluated. This threshold parameter (PCmax), derived from the SDT parameter d', indicates that detection is above threshold when subjects detect only 20-30% of the applied stimuli, as sham stimuli were detected also. The detectability increased with increasing velocity and up to a certain value with increasing amplitude. The threshold for movement detection was lower than 0.25 degree for the three faster angular velocities (0.1 degree s-1, 0.5 degree s-1, 0.6 degree s-1) and lower than 0.75 degree for the slowest velocity (0.05 degree s-1). The decision criterion beta, a measure for central processing which determines acuity, might reflect the central processing output on fusimotor neurones and thus be an indirect measure of the gamma-drive evoked by fusimotor neurones.

Adult↗