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At least 91 records · Page 5Linked to original sources
PubMed1989

Sequential ideal-observer analysis of visual discriminations.

Visual stimuli contain a limited amount of information that could potentially be used to perform a given visual task. At successive stages of visual processing, some of this information is lost and some is transmitted to higher stages. This article describes a new analysis, based on the concept of the ideal observer in signal detection theory, that allows one to trace the flow of discrimination information through the initial physiological stages of visual processing, for arbitrary spatio-chromatic stimuli. This ideal-observer analysis provides a rigorous means of measuring the information content of visual stimuli and of assessing the contribution of specific physiological mechanisms to discrimination performance. Here, the analysis is developed for the physiological mechanisms up to the level of the photoreceptor. It is shown that many psychophysical phenomena previously attributed to neural mechanisms may be explained by variations in the information content of the stimuli and by preneural mechanisms.

Attention↗
PubMed1984

Visualization and analysis of right heart blood flow patterns by contrast echocardiography.

UNLABELLED: The clinical utility of visualization of blood flow patterns across the tricuspid valve (TV) and pulmonary valve (PV) by M-mode contrast echocardiography was studied in 38 patients with documented valvular or congenital heart disease and in 15 controls. Diastolic turbulence was observed in the TV outflow side in three patients with tricuspid stenosis. Turbulent flow was also detected during systole in patients with septal defects (atrial septal defect in four patients and ventricular septal defect in one patient) in the right ventricular outflow tract and in three atrial septal defect patients also in the inflow tract, presumably because of increased volume of flow. Tricuspid regurgitation (11 patients) was characterized by retrograde laminar jet throughout systole, while in pulmonary regurgitation (six patients) retrograde flow was initially laminar although later on it might become turbulent. In pulmonary hypertension (29 patients) antegrade flow occurred approximately to mid-systole and then was interrupted by retrograde laminar flow which contributed to the mid-systolic closure of the pulmonary valve and pulmonary regurgitation in some cases. CONCLUSIONS: contrast echocardiography is a useful technique to analyse right heart blood flow patterns and may aid the diagnosis of various right heart abnormalities.

Captopril↗
PubMed1985

Spatio-temporal EEG measures and their application to human intracranially recorded epileptic seizures.

We describe analysis methods which involve the computation of band-integrated, intrachannel spectral measures from the EEG. These measures require only very general assumptions, have a simple interpretation and achieve significant data reduction, while providing a quantitative assessment of significant EEG modification at seizure or onset or in the course of seizure evolution. In developing these measures, we experimented with various measures derived from spatio-temporal power spectra. Bandpass (8-30 Hz) integrated relative energy measures appear to be the most useful since they objectively measure paroxysmal modification. Two such measures are illustrated in this report: the band-integrated power z-score (BIPZ), which is a quantitative measure designed to allow significance testing, and the band-integrated power ratio (BIPR), which is a simply calculated qualitative measure that behaves very similarly to the BIPZ measure and may be useful for real-time data screening. In addition to developing these intrachannel measures, we have also developed methods of displaying these measures in a format appropriate to the analysis of interchannel relationships. In a general sense, the displays provide objective information regarding the spatio-temporal dynamics of the EEG in a condensed format which is still readily understandable to the electroencephalographer. This analysis was applied to 29 spontaneous, depth-recorded seizures in 14 patients with the aim of identifying the initial locus of seizure activity in each seizure episode. The initial locus was defined as that location (or set of locations) to first exhibit statistically significant values of the BIPZ measure. The method was very effective in this regard, as shown by correspondence between the conclusions of this automated analysis and conventional visual analysis.

Brain↗
PubMed1989

The implementation of an autoregressive model with exogenous input in a single sweep visual evoked potential analysis.

Based on a model of signal-noise interaction, we present a method for single-sweep analysis of Visual Evoked Potentials. The EEG is represented as an autoregressive process and the single-sweep VEP as a filtered version of a reference signal taken as the running average of 20 consecutive sweeps. The algorithm for model identification and filtering is an ARX (AutoRegressive with eXogenous input) which provides a fast and efficient solution by means of a least squares approach. The choice of reference signal, as well as the complexity of the model, is also discussed. A further advantage of this approach is parameter reduction: all the single-sweep information is contained in 18 model coefficients and the reference signal.

Evoked Potentials, Visual↗
PubMed1990

Detection of mild coronary stenoses using the Dynamic Spatial Reconstructor.

The accuracy of the Dynamic Spatial Reconstructor (DSR) in the detection of moderate coronary artery stenoses was examined in 20 closed-chest dogs. Twenty-eight hollow plastic cylinders were embolized into the left coronary arteries and produced 25% to 56% reductions in arterial lumina diameter. For each dog, one three-dimensional (3-D) image of the heart was reconstructed from each DSR scan recorded during injection of contrast into the aortic root. Analysis involved blinded visual analysis by four independent observers of multiview projection images computed from the single 3-D image. Postmortem coronary angiograms of the isolated heart were considered definitive for location of the stenoses. Overall sensitivity of detection by DSR was 89% and specificity 81%. Sensitivity of detecting stenoses greater than or equal to 50% was 98%. Receiver operating characteristics (ROC) analysis showed that detection of stenoses in the left coronary arteries is of equal sensitivity and specificity.

Animals↗
PubMed1992

Postictal switch in blood flow distribution and temporal lobe seizures.

The ictal increase of regional cerebral blood flow has yet to be fully utilised in the investigation of focal seizures. Although single photon emission tomography (SPECT) is being increasingly used in the localisation of epileptic foci, the evolution and time courses of the peri-ictal perfusion changes have yet to be clarified. We performed serial SPECT studies in the interictal, ictal and immediate postictal states in 12 patients with refractory temporal lobe epilepsy to define the patterns and duration of peri-ictal cerebral blood flow changes. Visual analysis showed a constant pattern of unilateral global increases in temporal lobe perfusion during seizures which suddenly switched to a pattern of relative mesial temporal (hippocampal) hyperperfusion and lateral temporal hypoperfusion in the immediate postictal period. Quantitative analysis confirmed the visual assessment. Lateral temporal cortex ictal/normal side to side ratios were increased by mean 35.1% (95% confidence interval 21.8% to 48.4%) more in the ictal studies than in the interictal studies and mesial temporal cortex ratios increased by mean 30.8% (22.4% to 39.2%). In the postictal state, however, lateral temporal ratios were reduced by mean 7.7% (-15.8% to 0.4%) compared with interictal values, whereas mesial temporal perfusion was maintained compared with the interictal studies. These observations provide critical information for interpreting scans which can be used in the localisation of epileptic foci. This postictal switch in blood flow patterns may reflect the underlying metabolic processes of neuronal activation and recovery and have implications for understanding the neurobiology of human epileptic seizures.

Basal Ganglia↗
PubMed1983

Sharp targets are detected better against a figure, and blurred targets are detected better against a background.

There is growing evidence that the performance of perceptual tasks is often facilitated by perceived "figureness." Accuracy in detection and discrimination of targets is higher when the targets are presented in figural regions than when they are presented in ground regions of an image. This "figure superiority" might be a result of a functional specialization in the visual analysis of figure; recent theories have also assumed a functional specialization in the visual analysis of ground. If so, we might expect "ground superiority" in situations where task performance requires information available primarily through analysis of ground. We manipulated the spatial frequency of a small line segment and found that when it was sharp (i.e., the high-spatial-frequency components were present), it was detected better in figural regions, but when we blurred it (only the low-to-medium spatial frequencies were present) it was detected better in ground regions. These findings support the view that figure and ground analyses involve different specialized functions.

Adolescent↗
PubMed1989

[Visual EEG analysis in controlling intravenous anesthesia using propofol].

Since the discovery of brain waves by Berger, repeated efforts have been made to use the electroencephalogram EEG for monitoring and controlling anesthesia. Owing to its susceptibility to failure and the high expenditure regarding technology and personnel, the technique has not yet been adopted in routine anesthesia, however. In the study now reported an attempt was made to apply the positive experience with the recording and interpretation of EEG in the development of new anesthetic agents in the experimental laboratory, during routine clinical operations. The anesthetic used in the study was Propofol, an induction hypnotic that has only recently been introduced, together with nitrous oxide and repeated doses of fentanyl. Propofol is distinguished by its fast onset of action and short inactivation time; it is therefore suitable for induction and maintenance of anesthesia. The aim of the study was to maintain predetermined stages of sleep during anesthesia with the aid of visual on-line analysis of the EEG and to establish the dose of Propofol required for this purpose. The operations-general and orthopedic surgery-lasted 70-190 min (average duration: 120 min). In accordance with the randomization plan, the maintenance dose of Propofol was controlled in such a way that in ten patients light sleep levels (C0 to D1) and in the other ten deep sleep levels were maintained. The EEG was recorded via five active scalp electrodes (FP2, F4, C4, P4, O2) with reference to a joint electrode (A2). The stages of sleep were classified according to Kugler.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

A comparison of the sensitivities of adaptive tracking, eye movement analysis and visual analog lines to the effects of incremental doses of temazepam in healthy volunteers.

The effects of single oral doses of 5, 10, and 20 mg temazepam were evaluated with the adaptive tracking test, analysis of smooth-pursuit and saccadic eye movements, and visual analog lines in a placebo-controlled, double-blind, crossover experiment with 12 healthy volunteers. Pharmacodynamic testing was performed until 10 hours and pharmacokinetics were evaluated until 24 hours. Temazepam, 20 mg, caused effects in all tests, with peak effects occurring at 30 minutes. The 10 mg dose caused effects on saccadic eye movements and subjective scores of alertness, whereas 5 mg temazepam was detected only by analysis of saccadic eye movements. Linear relationships between plasma concentrations and effects were found in nine subjects for saccadic peak velocity and eight subjects for subjective scores of alertness. The results of this study demonstrate manifest differences in the sensitivities of performance tests and stress the importance of validation of methods when effects of drugs on human performance are studied.

Adult↗
PubMed1988

Visualization and analysis techniques for three dimensional information acquired by confocal microscopy.

Confocal Scanning Laser Microscopy (CSLM) is particularly well suited for the acquisition of 3-dimensional data of microscopic objects. In the CSLM a specific volume in the object is sampled during the imaging process and the result is stored in a digital computer as a three-dimensional memory array. Optimal use of these data requires both the development of effective visual representations as well as analysis methods. In addition to the well known stereoscopic representation method a number of alternatives for various purposes are presented. When rendering in terms of solid-looking or semitransparent objects is required, an algorithm based on a simulated process of excitation and fluorescence is very suitable. Graphic techniques can be used to examine the 3-dimensional shape of surfaces. For (near-)real time applications a representation method should not require extensive previous data-processing or analysis. From the very extensive field of 3-D image analysis two examples are given.

Cell Nucleus↗
PubMed1984

Rhodopsin and visual adaptation: analysis of photoreceptor thresholds in the isolated skate retina.

Photoreceptor thresholds in the isolated retina of the skate, determined by extracellular measurement of the photoreceptor potential during periods of light and dark adaptation, were analyzed in relationship to prevailing states of the visual pigment. The starting assumption of the analysis is that relative levels of three forms of the pigment molecule [native rhodopsin (R), a photoactivated intermediate (R*), and bleached pigment (B)] govern (quasi-) stable levels of threshold measured (a) during exposure of the retina to background light of fixed incident intensity (Ib), and (b) after irradiation that bleaches a defined fraction (B) of the rhodopsin. It is shown that experimental data are described well by the equation It/ It0 = (1 - B)-1 X F X (1 + 0(3)B), where F = [1 + 0(1)Ib(1 - B) + 0(2)B]. In this equation, It/ It0 is the relative threshold for detection of a test flash; (1 - B) approximates the relative efficiency of quantum capture; and 0(1) - 0(3) are constants. For values of 0(1) - 0(3) yielding an optimal fit to experimental data, log (It/ It0 ) approximately log F over a broad range of values of Ib and B. It is further shown that the algebraic form of the term F in the above equation is consistent with the predictions of a (steady-state) model for the role of the pigment molecule in photoreceptor adaptation. The model proposes that R* and B desensitize the photoreceptor by acting (in qualitatively similar fashion) to reduce the availability of E, an intracellular substance whose activation supports generation of the flash response. Results of the analysis are discussed in relation to the Dowling- Rushton equation (Dowling, 1960, 1963; Rushton , 1961), and to the results of more recent studies examining light and dark adaptation.

Adaptation, Ocular↗
PubMed1989

[Assessment of myocardial viability by quantitative analysis of stress Tl-SPECT--comparison with FDG-PET].

Stress Tl-201 tomography (SPECT) is widely used for evaluating myocardial viability. To assess its value, redistribution (RD) on SPECT was compared with metabolic imaging using FDG. Thirty patients with coronary artery disease underwent stress-3 hour Tl-201 SPECT and PET using N-13 ammonia and FDG. RD was classified into 4 grading, including complete RD (CR), incomplete RD (IR), persistent defect (PD) and additional minimal RD (MR) defined as no definite RD on visual analysis but faint RD with Bull's eye quantitative analysis (QNT). All but one segment with CR or IR were viable regions (normal or ischemic regions) by PET. Of 74 segments without RD on visual analysis, 31 segments (42%) had RD by QNT (MR). All of them were viable regions by PET. Thus, QNT identified 31 segments (63%) of the metabolically viable segments which the visual Tl-201 analysis did not show RD and classified as myocardial scar. However, even such QNT cannot detect ischemic myocardium in 18 segments (42%) containing metabolic activity on PET. These data indicate that QNT of RD on Tl-201 SPECT is considered as a valuable means for assessing myocardial ischemia.

Aged↗
PubMed1991

Regression analysis of visual field progression in low tension glaucoma.

Eighty four patients (168 eyes) with low tension glaucoma were retrospectively reviewed (mean follow-up was 28 months). The mean age was 66 years, and 69% were females. Regression analysis of their automated Humphrey fields (a mean of eight fields per eye) showed progression in 50% of patients and in 37% of eyes. There was no statistically significant difference between patients with progression and non-progression with respect to age (p less than 0.05) or intraocular pressure (p less than 0.5). Visual field defects were located most frequently in the superior hemifield in both groups of patients. A considerable proportion of patients had advanced field loss at the time of diagnosis.

Adult↗
PubMed1991

Can transcutaneous recordings detect gastric electrical abnormalities?

The ability of transcutaneous recordings of gastric electrical activity to detect gastric electrical abnormalities was determined by simultaneous measurements of gastric electrical activity with surgically implanted serosal electrodes and cutaneous electrodes in six patients undergoing abdominal operations. Transient abnormalities in gastric electrical activity were seen in five of the six patients during the postoperative period. Recognition of normal gastric electrical activity by visual analysis was possible 67% of the time and with computer analysis 95% of the time. Ninety four per cent of abnormalities in frequency were detected by visual analysis and 93.7% by computer analysis. Abnormalities involving a loss of coupling, however, were not recognised by transcutaneous recordings. Transcutaneous recordings of gastric electrical activity assessed by computer analysis can usually recognise normal gastric electrical activity and tachygastria. Current techniques, however, are unable to detect abnormalities in electrical coupling.

Diagnosis, Computer-Assisted↗
PubMed1985

Correlation functions in the analysis of visual evoked potentials.

Our "vision" laboratory has been working for several years on stimulation methods and data processing. We present here the results of an analysis of correlation functions between VEPs obtained by flashes and patterned stimulations. This study provides additional information about possible interpretations.

Evoked Potentials, Visual↗