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At least 253 records · Page 14Linked to original sources
PubMed2003

Nicotinic-glutamatergic interactions and attentional performance on an operant visual signal detection task in female rats.

Nicotinic systems have been shown to be critically involved in cognitive function including attention. Nicotine has been shown to improve performance on attentional tasks in humans with Alzheimer's disease, schizophrenia and attention deficit hyperactivity disorder. Nicotine has mixed effects on attentional accuracy in unimpaired rats with findings of increased, reduced or unaltered accuracy under different conditions. Nicotine effects on attentional function in rats might be more clearly seen in reversing impaired performance. The current study determined nicotine effects on attentional accuracy reduced by the NMDA receptor antagonist dizocilpine (MK-801). Sprague-Dawley rats (N=35) were trained on a food-motivated two-lever operant task with one lever correct after a brief visual signal (0.027-1.22 lx) for hits and the other lever correct after the absence of a signal for correct rejections. First, a dose response study of dizocilpine was conducted to determine the threshold for impairment. The rats were administered acute doses of dizocilpine (0, 12.5, 25 and 50 microg/kg, sc). The 50 microg/kg dose caused significant (p<0.0005) reduction in percent hit at the four highest signal intensities. Percent correct rejection was also significantly lowered by this dose (p<0.005). No effect was seen with 12.5 microg/kg and only minimal effect seen with 25 microg/kg. Then, nicotine-dizocilpine interactions were investigated. The rats were administered acute doses of dizocilpine (0, 37.5 and 50 microg/kg, sc) and nicotine (0, 25 and 50 microg/kg, sc), alone or in combination. Percent hit was affected by nicotine and dizocilpine in a complex fashion with only the nicotinexdizocilpinexsignal intensity interaction being significant (p<0.05). Percent correct rejection showed a more straightforward effect. Percent correct rejection was significantly reduced by 50 microg/kg dizocilpine (p<0.025). The addition of 25 microg/kg of nicotine significantly (p<0.025) reversed the dizocilpine-induced reduction of correct rejection. This study shows that dizocilpine reduces signal detection accuracy in a dose-dependent fashion. Nicotine can partially counteract an aspect of this reduction by reversing the dizocilpine-induced reduction of correct rejection.

Animals↗
PubMed2001

Using signal detection methods for analysis of operant performance in mice.

Several factors account for murine cognitive abilities, and manipulation of genes which would act at the effector molecules involved in stimulus processing, reward-related properties and/or motor output can easily confound behavioural data obtained from mouse mutants responding on cognitive tasks. Therefore, tests may be needed which allow a better dissociation between true cognitive processes (accuracy) and other factors that may alter performance (motor or motivational bias). Part of this can be achieved by using methods which enable parametric variation of task difficulty. Part of it can also be achieved by using data analysis that allows a distinction between accuracy and bias, such as the mathematical methods of signal detection theory (SDT). SDT formally addresses the possibility that a given gene product or lack thereof affects performance by affecting motivation rather than cognition. It proposes that performance in a task depends on two factors, that is the sensitivity (or accuracy) of the neural systems mediating a cognitive process and the subject's motivational state, the latter of which can be represented as bias. SDT analysis can be easily applied to murine data. This overview will discuss the advances and limitations of the various SDT measures and illustrate the value of this type of analysis for understanding cognitive performance of mice.

Animals↗
PubMed2001

Estimation of single motor unit conduction velocity from surface electromyogram signals detected with linear electrode arrays.

This work addresses the problem of estimating the conduction velocity (CV) of single motor unit (MU) action potentials from surface EMG signals detected with linear electrode arrays during voluntary muscle contractions. In ideal conditions, that is without shape or scale changes of the propagating signals and with additive white Gaussian noise, the maximum likelihood (ML) is the optimum estimator of delay. Nevertheless, other methods with computational advantages can be proposed; among them, a modified version of the beamforming algorithm is presented and compared with the ML estimator. In real cases, the resolution in delay estimation in the time domain is limited because of the sampling process. Transformation to the frequency domain allows a continuous estimation. A fast, high-resolution implementation of the presented multichannel techniques in the frequency domain is proposed. This approach is affected by a negligible decrease in performance with respect to ideal interpolation. Application of the ML estimator, based on two-channel information, to ten firings of each of three MUs provides a CV estimate affected by a standard deviation of 0.5 m s(-1); the modified beamforming and ML estimators based on five channels provide a CV standard deviation of less than 0.1 m s(-1) and allow the detection of statistically significant differences between the CVs of the three MUs. CV can therefore be used for MU classification.

Action Potentials↗
PubMed2000

Stochastic resonance and signal detection in an energy detector--implications for biological receptor systems.

Stochastic resonance is demonstrated in a simple energy detector model, as a non-monotonic relationship between signal-to-noise ratio and detection of a sinusoid signal in bandpass-limited Gaussian noise. The behaviour of the model detecting signals of various intensities and signal-to-noise ratios was investigated. Significant improvement in detection was obtained by adding noise for mean signal intensities below the detection criterion of the detector. The range of usable noise levels, however, may be too small to be biologically meaningful. It is demonstrated that improving detection in the analysed model by adding noise to an otherwise undetectable signal is only at best as efficient as what can be obtained by adjusting the criterion to the signal-to-noise ratio. Improving detection by means of stochastic resonance is thus a sub-optimal strategy. It is speculated whether a demonstration of stochastic resonance in a biological system indicates any adaptive significance. More than anything, it indicates the presence of a mismatch between receptor sensitivity and the signal-to-noise ratio of the experiment, not the cause of this mismatch.

Animals↗
PubMed1998

Generalization of the Theory of Signal Detectability to n-Event m-Dimensional Forced-Choice Tasks.

This paper presents a generalization of the theory of signal detectability to n-event forced-choice tasks where the evidence can be modelled by an m-dimensional vector. The generalization is based on a nonparametric model that encompasses decision rules for maximizing the proportion of correct decisions. The model assumes that observers identify events by partitioning a decision space of dimension n-1 with a template. Translating the template by varying the decisional bias yields a set of receiver operating characteristic (ROC) surfaces. Following B. K. Scurfield [1996, J. Math. Psych. 40, 253-269], event-discriminability is defined by considering the Shannon entropy of the volumes under the ROC surfaces. The resultant discriminability measure is interpreted with respect to the random vectors assumed to be associated with the decision space and shown to equate with the channel capacity of an observer in a multiple-interval forced-choice task. Copyright 1998 Academic Press.

Journal Article↗
PubMed1979

Residual sensory capacities of the deaf: a signal detection analysis of a visual discrimination task.

This experiment compared the visual sensory sensitivity of deaf and hearing subjects in a signal detection paradigm. Subjects (ns = 6) were required to give forced-choice responses to a brightness discrimination task under three stimulus probability conditions (0.25, 0.50, and 0.75). A total of 1,800 trials were given to each subject and utilized to construct isosensitivity functions and d' and Beta, indices for sensory sensitivity and response bias, respectively. The results showed that no enhanced sensory sensitivity is present for these deaf children and questions the classical sensory compensation hypothesis. Furthermore, the deaf subjects responded in a relatively bias-free manner to variations in stimulus probability.

Attention↗
PubMed1963

Signal detection in the rat.

An auditory detection experiment was performed with rats as subjects, and the data were analyzed with a signal detection model. Rats were run at fixed sound pressure levels, and their responses were partitioned so that operating characteristics could be constructed. Measures of detectability, (d(e))((1/2)), were calculated from the operating characteristics, and show that (d(e))((1/2)) is a function of sound pressure levels, rising as these levels rise.

Animals↗
PubMed2005

Defining response in clinical trials for obsessive-compulsive disorder: a signal detection analysis of the Yale-Brown obsessive compulsive scale.

OBJECTIVE: Many studies of the treatment of obsessive-compulsive disorder (OCD) have used percent reduction cutoffs on the Yale-Brown Obsessive Compulsive Scale (YBOCS) to classify patients as treatment responders. However, reduction criteria have varied from 20% to 50%, with studies of cognitive-behavioral therapy (CBT) using a more stringent criterion than studies of pharmacotherapy. The aim of this retrospective investigation was to determine optimal YBOCS reduction criteria for classifying patients as responders. METHOD: Data from 87 adult clinic and research outpatients meeting DSM-IV-TR criteria for OCD according to structured interview were examined, comparing the percent YBOCS reduction from pretreatment to posttreatment with 2 "gold standard" criteria from the Clinical Global Impressions (CGI) scale: much or very much improved and mild illness or better. Signal detection analyses were used to determine the sensitivity, specificity, predictive value of a positive test, predictive value of a negative test, and efficiency of various YBOCS reduction cutoffs. RESULTS: A YBOCS reduction cutoff of 30% was optimal for predicting improvement on the CGI. The 20% cutoff used by many pharmacologic studies resulted in a high number of false positives, whereas the 50% cutoff used by most CBT studies resulted in a high number of false negatives. For predicting mild illness or better at posttreatment, a YBOCS reduction cutoff of 40% to 50% was optimal. CONCLUSIONS: A YBOCS reduction criterion of 30% appears to be optimal for determining clinical improvement, whereas a 40% to 50% reduction criterion is appropriate for predicting mild illness at posttreatment. Future studies should employ a standard definition of treatment response in order to facilitate cross-study comparisons.

Adult↗
PubMed1994

Signal-detection analysis of the Müller-Lyer and the Horizontal-Vertical illusions.

Perceptual error in the Müller-Lyer and the Horizontal-Vertical illusions was quantified using nonparametric signal-detection measures of sensitivity and response bias. Sensitivity scores were positively related to signal strength with the greatest values observed for the strongest signals. Sensitivity at each signal strength did not differ between the two illusions. Response-bias scores were inversely related to signal strength, with the most conservative biases observed for the strongest signals. Response biases for each signal strength were significantly more conservative for the Horizontal-Vertical than for the Müller-Lyer illusion.

Adult↗
PubMed1992

Maximum likelihood estimation of signal detection model parameters for the assessment of two-stage diagnostic strategies.

The methodology of Receiver Operating Characteristic curves based on the signal detection model is extended to evaluate the accuracy of two-stage diagnostic strategies. A computer program is developed for the maximum likelihood estimation of parameters that characterize the sensitivity and specificity of two-stage classifiers according to this extended methodology. Its use is briefly illustrated with data collected in a two-stage screening for auditory defects.

Algorithms↗
PubMed1993

Signal-detection outcomes on heartbeat and respiratory resistance detection tasks in male and female subjects.

Male and female subjects were compared on heartbeat, respiratory resistance, and light-tone signal-detection tasks. Subjects judged whether a series of 10 tones was coincident with their heartbeats; whether an external load added to the airway was either present or absent during targeted inspiratory cycles; and whether a series of 10 light flashes was matched with auditory tones presented following a fixed delay of either 50 or 100 ms. Nonparametric indices of perceptual sensitivity and response bias indicated that men were more sensitive than women on the resistive load task (p < .05) and on the heartbeat task (p = .07). Performance on the light-tone task was virtually identical. All subjects used a stricter criterion on the respiratory resistance task than on either the heartbeat or the light-tone task; women employed a stricter criterion than men on the heartbeat task. The gender differences may be understood in terms of lateralization of central processing of somesthetic sensory information.

Acoustic Stimulation↗
PubMed2006

The use of embolic signal detection in multicenter trials to evaluate antiplatelet efficacy: signal analysis and quality control mechanisms in the CARESS (Clopidogrel and Aspirin for Reduction of Emboli in Symptomatic carotid Stenosis) trial.

BACKGROUND AND PURPOSE: The CARESS (Clopidogrel and Aspirin for Reduction of Emboli in Symptomatic carotid Stenosis) trial proved the effectiveness of the combination of clopidogrel and aspirin compared with aspirin alone in reducing presence and number of microembolic signals (MES) in patients with recently symptomatic carotid stenosis. The present study aimed at installing primary and secondary quality control measures in CARESS because MES evaluation relies on subjective judgment by human experts. METHODS: As primary quality control, centers participating in CARESS evaluated a reference digital audio tape (DAT) before the study containing both MES and artifacts. Interobserver agreement of classifying signals as MES was expressed as proportions of specific agreement of positive ratings (ps+/-values). For all DATs included in CARESS (n=300), online number of MES and off-line number of MES read by the central reader were compared using correlation coefficients. As secondary control, a sample of 16 of 300 DATs was cross-validated by another independent reader (post-trial validator). RESULTS: For the reference tape, the cumulative ps+/-value was 0.894 based on 12 of 14 observers. Two observers with very different results improved after a training procedure. Agreement between post-trial validator and central reader was ps+=0.805, indicating very good agreement. Correlation between online evaluation and off-line evaluation of DATs was very good overall (cumulative rho=0.84; P<0.001). CONCLUSIONS: Multicenter studies using MES as outcome parameter are feasible. However, primary and secondary quality control procedures are important.

Aspirin↗
PubMed1976

Acupuncture analgesia and radiant-heat pain: a signal-detection analysis.

Responses to radiant-heat stimulation to the back of the hand were obtained during baseline conditions and during acupuncture sessions. Signal-detection methodology and analysis were used to determine whether acupuncture affects d' (changes physiologic processes) relative to pain report. A binary rather than a rating-scale procedure was used to obtain more accurate measures of sensitivity. Results indicated that acupuncture decreased sensitivity only at intensity levels that were never described as painful.

Acupuncture Therapy↗
PubMed1993

Seashore Rhythm test: comparison of Signal Detection Theory and standard scoring procedures.

The effects of age and instructional set on Seashore Rhythm test performance were examined with standard scoring and Signal Detection Theory (SDT) procedures. Neurologically intact young (17-28 years) and old (65-92 years) subjects were given standard test instructions with sentences added which stated that specific proportions of the test stimuli would be identical or different. Age differences in d' scores were highly correlated with standard Rhythm scores. While standard scores were unaffected by instructional set, all three SDT measures of response criteria detected effects of instructional set, or an age by instructional set interaction. SDT scoring of the Rhythm test yields a measure of auditory sensitivity comparable to standard methods and detects response bias on the lest that standard procedures cannot.

Journal Article↗
PubMed1989

Influence of adult castration on the olfactory sensitivity of the male rat: a signal detection analysis.

The effect of adult castration on the male rat's ability to detect ethyl acetate odor was measured with high-precision olfactometry and a go-no-go signal detection task. Castration was found to significantly mitigate the tendency observed in sham castrates to improve detection performance across an 18-week postoperative test period. No significant castration-related alterations on the responsivity or S+ response latency measures were observed. These findings indicate that castration influences the male rat's ability to improve odor detection performance over time, although it is not known whether this effect is attributable to sensory or to memory mechanisms.

Animals↗
PubMed1999

Frequency filtering improves ultrasonic embolic signal detection.

Problems in detection of Doppler cerebral embolic signals primarily occur for embolic signals of low relative intensity. A characteristic feature of embolic signals is that the intensity increase is maximal over a narrow frequency band. Therefore, frequency filtering of the data might improve embolic signal relative intensity and detectability. We implemented an off-line finite impulse response filter in software running on a commercially available transcranial Doppler system, using the time-domain audio data as input. The range of the filter was chosen by placing a box around the embolic signal on the spectral display. One hundred consecutive embolic signals from patients with carotid stenosis were analyzed; all had been recorded by a bigate system and the signal was analyzed in both proximal and distal channels. There was a highly significant increase in embolic signal relative intensity following frequency filtering; mean (SD) proximal channel prefiltering 12.75 (4.83) dB, postfiltering 16.36 (4.93) dB; distal channel prefiltering 13.42 (4.98) dB, postfiltering 16.60 (5.11) dB, for both p < 0.001. Despite all embolic signals being audible and visible in at least one channel on the frequency spectral display, in 17 cases, the amplitude increase associated with the embolic signal could not be clearly seen in time-domain data of one or both channels prior to filtering. Following frequency filtering, this was reduced to 5. Incorporation of such a frequency-filtering approach to an online system is likely to improve the sensitivity of online detection for embolic signals of low relative intensity.

Carotid Stenosis↗