Cognitive function after open-heart surgery: Are postoperative neuropsychological deficits caused by cardiopulmonary bypass?

Despite the many technological developments in arterial perfusion and cardiac surgical procedures, open-heart surgery is still believed to pose a significant risk for cerebral injury. There are several potential causes of brain damage during open-heart surgery, including prolonged or severe arterial hypotension, as well as emboli emanating from the cardiopulmonary bypass circuit or the operative field. This article reviews the available neuropsychological studies of outcome following cardiac valve replacement and coronary artery bypass grafting. Because both procedures are life-saving operations, the research in this area has been quasi-experimental and fraught with methodological problems. Nonetheless, the findings converge to suggest that cognitive dysfunction occurs after open-heart surgery, and that the deficits are attributable, at least in part, to factors specific to the operation or to the patient being maintained on cardiopulmonary bypass. Preliminary findings suggest that embolization is the primary cause of perioperative deficits in uncomplicated operations. Studies have also consistently found preoperative deficits in this population, suggesting that neuropsychological dysfunction is caused by severe chronic cardiac disease as well as open-heart surgery.     

A probabilistic multidimensional scaling with unique axes1

Abstract: A probabilistic multidimensional scaling model is proposed. The model assumes that the coordinates of each stimulus are normally distributed with variance Σ_i = diag(σ²₁, … σ²_Ri). The advantage of this model is that axes are determined uniquely. The distribution of the distance between two stimuli is obtained by polar coordinates transformation. The method of maximum likelihood estimation for means and variances using the EM algorithm is discussed. Further, simulated annealing is suggested as a means of obtaining initial values in order to avoid local maxima. A simulation study shows that the estimates are accurate, and a numerical example concerning the location of Japanese cities shows that natural axes can be obtained without introducing individual parameters.     

A new computational method to fit the weighted euclidean distance model

This paper describes a computational method for weighted euclidean distance scaling which combines aspects of an analytic solution with an approach using loss functions. We justify this new method by giving a simplified treatment of the algebraic properties of a transformed version of the weighted distance model. The new algorithm is much faster than INDSCAL yet less arbitrary than other analytic procedures. The procedure, which we call SUMSCAL (subjectivemetricscaling), gives essentially the same solutions as INDSCAL for two moderate-size data sets tested.Comments by J. Douglas Carroll and J. B. Kruskal have been very helpful in preparing this paper.     

A test of the hypothesis that Cronbach's alpha reliability coefficient is the same for two tests administered to the same sample

In measurement studies the researcher may wish to test the hypothesis that Cronbach's alpha reliability coefficient is the same for two measurement procedures. A statistical test exists for independent samples of subjects. In this paper three procedures are developed for the situation in which the coefficients are determined from the same sample. All three procedures are computationally simple and give tight control of Type I error when the sample size is 50 or greater.The author is indebted to Jerry S. Gilmer for development of the computer programs used in this study.     

A stochastic multidimensional scaling procedure for the empirical determination of convex indifference curves for preference/choice analysis

The vast majority of existing multidimensional scaling (MDS) procedures devised for the analysis of paired comparison preference/choice judgments are typically based on either scalar product (i.e., vector) or unfolding (i.e., ideal-point) models. Such methods tend to ignore many of the essential components of microeconomic theory including convex indifference curves, constrained utility maximization, demand functions, et cetera. This paper presents a new stochastic MDS procedure called MICROSCALE that attempts to operationalize many of these traditional microeconomic concepts. First, we briefly review several existing MDS models that operate on paired comparisons data, noting the particular nature of the utility functions implied by each class of models. These utility assumptions are then directly contrasted to those of microeconomic theory. The new maximum likelihood based procedure, MICROSCALE, is presented, as well as the technical details of the estimation procedure. The results of a Monte Carlo analysis investigating the performance of the algorithm as a number of model, data, and error factors are experimentally manipulated are provided. Finally, an illustration in consumer psychology concerning a convenience sample of thirty consumers providing paired comparisons judgments for some fourteen brands of over-the-counter analgesics is discussed.     

Spatial and conjoint models based on pairwise comparisons of dissimilarities and combined effects: Complete and incomplete designs

In pairwise multidimensional scaling, a spatial representation for a set of objects is determined from comparisons of the dissimilarity of any two objects drawn from the set to the dissimilarity of other pairs of objects drawn from that set. In pairwise conjoint scaling, comparisons among the joint effects produced by pairs of objects, where the objects in a pair are drawn from separate sets, are used to determine numerical representations for the objects in each set. Monte Carlo simulations of both pairwise dissimilarities and pairwise conjoint effects show that Johnson's algorithm can provide good metric recovery in the presence of high levels of error even when only a small percentage of the complete set of pairwise comparisons are tested.     

Analysis of the elements of attention: A neuropsychological approach

A model for conceptualizing the components or elements of attention is presented. The model substitutes for the diffuse and global concept of attention a group of four processes and links them to a putative system of cerebral structures. Data in support of the model are presented; they are derived from neuropsychological test scores obtained from two samples, the first consisting of 203 adult neuropsychiatric patients and normal control subjects, and the second, an epidemiologically-based sample of 435 elementary school children. Principal components analyses of test scores from these two populations yielded similar results: a set of independent elements of attention that are assayed by different tests. This work presents a heuristic for clinical research in which the measurement of attention is essential.     

Restricted multidimensional scaling models for asymmetric proximities

Restricted multidimensional scaling models [Bentler & Weeks, 1978] allowing constraints on parameters, are extended to the case of asymmetric data. Separate functions are used to model the symmetric and antisymmetric parts of the data. The approach is also extended to the case in which data are presumed to be linearly related to squared distances. Examples of several models are provided, using journal citation data. Possible extensions of the models are considered. This research was supported in part by USPHS Grant 0A01070, P. M. Bentler, principal investigator, and NIMH Grant MH-24819, E. J. Anthony and J. Worland, principal investigators. The authors wish to thank E. W. Holman and several anonymous reviewers for their valuable suggestions concerning this research.     

Perception of autonomic reactions and actual heart rate in phobic patients

The relationship between perceived physiological arousal and actual heart-rate reactions was studied in two behavioral test situations. The subjects were 70 phobic patients (34 social phobics and 36 claustrophobics) who were given the general form of the Autonomic Perception Questionnaire about 1 month before the respective behavioral test and the specific form immediately after the test. The results showed significant correlations between APQ and actual heart rate for the social phobics, while the picture was more complicated for the claustrophobics. The implications of these results are discussed.This research was supported by Grant 05452 from the Swedish Medical Research Council.