Pairs Of Time Points Research Articles

Is there evidence for amodality of mental representation in categorization tasks of words and pictures?

Experiment and methods: Three well trained subjects carried out two different tasks: categorization and pattern comparison. Two kinds of stimuli were given in blocks: words and pictures. The two words or two pictures were presented with an interstimulus interval on a computer screen. For pattern comparison the subject has to decide about the identity of the two words or pictures. In case of categorization the subjects have to classify the two words or pictures. Thereby a category concept must be activated in contrast to pattern comparison. The EEG was recorded from 19 scalp electrodes (10 /20 system, ear lob reference, 256 Hz). Only artifact-free trials with correct positive answers were included in further analysis. Instantaneous coherence analysis (see e.g. Schack et al. 1999) was performed for 39 electrode pairs. The frequency band 13-20 Hz allowed the best discrimination between categorization and pattern comparison. Therefore, the time courses of coherence with regard to this frequency band were analyzed. Maximal coherence values were calculated for each trial and each electrode pair within the time interval from the presentation of the second item up to the end of the task. On the basis of calculating the correlation between the coherence vectors of all pairs of time points within the same time interval the single trials were subdivided into segments with stable coherence values. The segments were clustered into six classes. The time points of beginning, the duration and the mean coherence values of the segments of each cluster were calculated. Results: − Subjects need the same reaction time for classifying words and pictures. − The values of maximal coherence for the electrode pairs T3/C3, C3/Cz, T3/T5, C3/P3, F3/Pz are significantly higher for categorization than for pattern comparison both for word and for picture representation. At the same time they are not different with regard to the kind of stimulus both for categorization and for pattern comparison. − The distribution of segments of the cluster with high coherence values within the left hemisphere differs extremely with regard to the modality both for presentation of words and pictures (see Fig.1).

STCSP – structured temporal constraint satisfaction problems

Temporal Constraint Satisfaction Problems (TCSP) is a welldknown approach for representing and processing temporal knowledge. Important properties of the knowledge can be inferred by computing the minimal networks of TCSPs. Consistency and feasible values are immediately obtaineds computing solutions can be assisted. Yet, in general, computing the minimal network of a disjunctive TCSP is intractable. The minimal network approach requires computation of the full network in order to answer a query. In this paper we characterize TCSPs for which subsets of the minimal network can be computed without having to compute the whole network. The partial computation is enabled by decomposition of the problem into a tree of subdproblems that share at most pairs of time points. Such decompositions are termed sim/2dtree decompositions. For TCSPs that have sim/2dtree decompositions, minimal constraints of input propositions can be computed by independent computations of the minimal networks of the subdproblems at most twice. It is also shown that the sim/2dtree characterization is a minimal set of conditions. The sim/2dtree decomposition extends former results about decomposition of a TCSP into bidconnected components. An algorithm for identifying a sim/2dtree decomposition of a TCSP is provided as well. Finally, the sim/2dtree decomposition is generalized in an inductive manner, which enables components of a decomposition to be further decomposed. For that purpose a model of Structured Temporal Constraint Satisfaction Problems (STCSP^{(n)},\ 0 \leq n), where STCSP^{(0)} is simply TCSP, STCSP^{(1)} is a set of STCSP^{(0)}s, and in general, STCSP^{(n)} for 1 \leq n is a set of STCSP^{(n-1)}s, is introduced.

Within-subject variability of differences between conventional and automated blood pressure measurements in pregnancy

Objective: To determine whether measured differences between standard mercury sphygmomanometry and the SpaceLabs 90207 ambulatory blood pressure monitor in pregnant women remain constant during 24 h measurements. Study design: Repeated comparisons between standard mercury sphygmomanometry and Spacelabs 90207 were performed at nine predetermined time points during 24 h ambulatory blood pressure measurements in a group of ten pregnant women with various pregnancy complications, including hypertension. Individual and group differences between standard mercury sphygmomanometry and SpaceLabs 90207 were calculated for each time point. Friedman's ANOVA was used to test stability of differences across time. Results: Mean group differences (standard deviation) between mercury sphygmomanometry and the SpaceLabs 90207 were −2 (6) mmHg and 3 (7) mmHg for systolic and diastolic pressure respectively. For systolic pressure the differences between time points were not statistically significant. Although a statistical significant trend was found for diastolic pressure differences ( P<0.05), none of the contrasts between any pair of time points reached statistical significance. For both systolic and diastolic pressure the minimal and maximal difference lay at least 10 mmHg apart in seven patients. Conclusions: Despite standardisation and training, a substantial within-subject variability of the pressure difference between observers and SpaceLabs was found in this heterogeneous group of women. However, a systematic time-related effect on this pressure difference could not be demonstrated. The pressure difference between both methods cannot be estimated with great precision. This is a serious impediment for the clinical interpretation of automated or ambulatory blood pressure data.

Repeated measures ANOVA for responses developing over time

Repeated measures ANOVA for responses developing over time

A Novel Methodology for Quantitating the Enhancement of Cutaneous Delayed-Type Hypersensitivity by IMREG-1: A Measure of the Immunopotentiation of Cell-Mediated Immunity

IMREG-1, a low-molecular-weight immunomodulator derived from normal human leukocyte dialysates, has been shown to enhance cutaneous delayed-type hypersensitivity (DTH) responses to recall antigens. Both IMREG-I and the biologically active peptides (Tyr-Gly[YG] and Tyr-Gly-Gly[YGG]) identified therein are able to accelerate and enhance DTH in a concentration-dependent manner. In this study, we describe a novel methodology for analyzing and quantitating this response and demonstrate its use with data comparing drug to placebo. Subjects demonstrating prior sensitivity to a recall antigen (tetanus toxoid) received intradermal injections of tetanus toxoid alone (control) and either dilutions of IMREG-1 plus antigen, or placebo plus antigen, on the volar surface of the forearm. The response, as measured by area of erythema, was calculated and plotted as a function of time. The area under the resulting curve (AUC) was then determined by use of the trapezoidal rule, whereby the area of a trapezoid formed between each sequential pair of time points was calculated. The AUC computed for each site receiving a dilution of IMREG-1 or placebo (test) was compared with the AUC computed at the site that received antigen alone (control) by means of a test to control (T/C) ratio. The respective T/C ratios for designated dilutions of IMREG-1 or placebo provided a basis of comparison between responses to IMREG-1 and to placebo, while also controlling for individual sensitivity in response to antigen. We demonstrate in this study that the enhanced response to IMREG-1 plus antigen is statistically different from that seen with placebo plus antigen. This response, as a function to time, predominantly appears in the 12- to 24-hr period after injection, illustrating the ability of the immunomodulator to accelerate, enhance, and sustain a DTH response. We further conclude that the effect of IMREG-1 in this context is one of immunopotentiation of cell-mediated immunity.

A non-reified temporal logic

A temporal logic is presented for reasoning about propositions whose truth values might change as a function of time. The temporal propositions consist of formulae in a sorted first-order logic, with each atomic predicate taking some set of temporal arguments as well as a set of non-temporal arguments. The temporal arguments serve to specify the predicate's dependence on time. By partitioning the terms of the language into two sorts, temporal and non-temporal, time is given a special syntactic and semantic status without having to resort to reification. The benefits of this logic are that it has a clear semantics and a well-studied proof theory. Unlike the first-order logic presented by Shoham, propositions can be expressed and interpreted with respect to any number of temporal arguments, not just with respect to a pair of time points (an interval). We demonstrate the advantages of this flexibility. In addition, nothing is lost by this added flexibility and more standard and usable syntax. To prove this assertion we show that the logic completely subsumes Shoham's temporal logic [19].

Temporal constraint networks

This paper extends network-based methods of constraint satisfaction to include continuous variables, thus providing a framework for processing temporal constraints. In this framework, called temporal constraint satisfaction problem (TCSP), variables represent time points and temporal information is represented by a set of unary and binary constraints, each specifying a set of permitted intervals. The unique feature of this framework lies in permitting the processing of metric information, namely, assessments of time differences between events. We present algorithms for performing the following reasoning tasks: finding all feasible times that a given event can occur, finding all possible relationships between two given events, and generating one or more scenarios consistent with the information provided. We distinguish between simple temporal problems (STPs) and general temporal problems, the former admitting at most one interval constraint on any pair of time points. We show that the STP, which subsumes the major part of Vilain and Kautz's point algebra, can be solved in polynomial time. For general TCSPs, we present a decomposition scheme that performs the three reasoning tasks considered, and introduce a variety of techniques for improving its efficiency. We also study the applicability of path consistency algorithms as preprocessing of temporal problems, demonstrate their termination and bound their complexities.

Glucose disappearance rate in rhesus monkeys: Some technical considerations.

The intravenous glucose tolerance test (IVGTT) has been widely used as a tool to assist in the diagnosis of diabetes mellitus. Glucose disappearance rate (KG) is calculated as an indicator of relative glucose tolerance; however, a standardized dose, consistent sampling times, and a consistent formula for the calculation of KG have not yet been established for rhesus monkeys. Interpretation of results reported by different laboratories has, therefore, been rendered difficult. In the present study, 48 IVGTTs obtained from 33 male rhesus monkeys ranging widely in glucose tolerance have been analyzed. Various formulas for calculating KG values have been tested in all experiments including a range of different pairs of time points, as well as the t1/2. Regression analysis revealed that the loge transformation of the plasma glucose levels obtained after an intravenous glucose load were best fitted with a straight line during the period between five and 20 minutes (R2 = 0.97 ± 0.005). The use of time points prior to the five-minute value tended to produce spuriously larger KG values, while sampling points that were later than 30 min occasionally produced an invalid KG because in some monkeys the plasma glucose levels had already returned to basal levels. The advantages of using the five- and 20-minute glucose levels in calculating the KG include (1) the optimal reflection of tissue uptake of glucose; (2) the relatively short sampling time required to obtain an accurate, consistent, and meaningful value for KG; and (3) the relative ease in the calculation of KG.

Local times of stochastic processes with positive definite bivariate densities

A new class of stochastic processes, called processes of positive bivariate type, is defined. Such a process is typically one whose bivariate density functions are positive definite, at least for pairs of time points which are sufficiently mutually close. The class includes stationary Gaussian processes and stationary reversible Markov processes, and is closed under the operations of composition and convolution. The purpose of this work is to show that the local times of such processes can be investigated in a natural way. One of the main contributions is an orthogonal expansion of the local time which is new even in the well-studied stationary Gaussian case. The basic tool in its construction is the Lancaster-Sarmanov expansion of a bivariate density in a series of canonical correlations and canonical variables.