Least-squares approximation of an improper correlation matrix by a proper one

An algorithm is presented for the best least-squares fitting correlation matrix approximating a given missing value or improper correlation matrix. The proposed algorithm is based upon a solution for Mosier's oblique Procrustes rotation problem offered by ten Berge and Nevels. A necessary and sufficient condition is given for a solution to yield the unique global minimum of the least-squares function. Empirical verification of the condition indicates that the occurrence of non-optimal solutions with the proposed algorithm is very unlikely. A possible drawback of the optimal solution is that it is a singular matrix of necessity. In cases where singularity is undesirable, one may impose the additional nonsingularity constraint that the smallest eigenvalue of the solution be , where is an arbitrary small positive constant. Finally, it may be desirable to weight the squared errors of estimation differentially. A generalized solution is derived which satisfies the additional nonsingularity constraint and also allows for weighting. The generalized solution can readily be obtained from the standard unweighted singular solution by transforming the observed improper correlation matrix in a suitable way.     

Correlation between Changes in Stress-Induced Corticosterone Secretion and GR mRNA Levels

The current study was conducted to determine the potential relationship between stress-induced corticosterone secretion and corticosteroid receptor mRNA levels after 5 days of intermittent stress. In particular, we were interested in the rate at which animals terminate a stress response, and how this termination may be altered by repeated stress. Adult male Sprague-Dawley rats were subjected to either 5 days of restraint stress or 5 days of an unpredictable stress paradigm. Restraint-stress induced corticosterone secretion was measured on Days 1 and 5 in both groups, and animals were killed on Day 6. Glucocorticoid receptor (GR), and mineralocorticoid (MR) mRNA levels were determined using in-situ hybridization techniques. Five days of restraint stress caused an habituation of the plasma corticosterone response to stress measured 60 and 90 min post-stress initiation; this pattern of corticosterone secretion was not observed in the animals subjected to unpredictable stress. Five days of either stress paradigm did not alter MR mRNA levels measured within the hippocampus or GR mRNA levels within the hippocampus or the medial parvocellular division of the paraventricular nucleus of the hypothalamus (mpPVN). However, an individual's GR mRNA levels measured within the CA1/2 region of the hippocampus and the mpPVN were significantly correlated with the degree of habituation of the corticosterone response to stress measured on Day 5. This suggests that an increase in the rate of termination of the stress response and levels of GR within the hippocampus and mpPVN may be functionally related.     

Effects of Emotional Experience for Abstract Words in the Stroop Task

In this study, we examined the effects of emotional experience, a relatively new dimension of emotional knowledge that gauges the ease with which words evoke emotional experience, on abstract word processing in the Stroop task. In order to test the context‐dependency of these effects, we accentuated the saliency of this dimension in Experiment 1A by blocking the stimuli such that one block consisted of the stimuli with the highest emotional experience ratings and the other block consisted of the stimuli with the lowest emotional experience ratings. We attenuated the saliency of this dimension in Experiment 1B by intermixing the stimuli. We observed slower color naming performance for words with higher emotional experience ratings only in Experiment 1A, suggesting that the dimension of emotional experience is an aspect of semantic representation for abstract words but that its influence can be modulated by context. We interpret these results more generally using Vigliocco, Meteyard, Andrews, and Kousta's (2009) framework of semantic representation, and more specifically using Cohen, Dunbar, and McClelland's (1990) model of Stroop task performance.     

Associations Among Body Mass Index,Depression, and Family Factors Across Two Generations

In this pilot study, we examined the relationship between health factors, sociodemographic factors, and body mass index (BMI) across two generations (n = 41 parent-child pairs). Generation 1 study variables included parent- and family-focused characteristics and health variables, the Generation 2 variables included child demographic factors, and the outcome variable was youths’ physical health (operationalized as BMI). Regression models revealed that Generation 1 variables, taken together, accounted for 26% of the variance in youth BMI. However, only the parent’s mental health symptoms (i.e., depression symptoms) made a unique contribution to the variance in youth BMI. Logistic regression analysis revealed that the youths’ race and age—but no other demographic factor—were significantly related to youth BMI-for-age. Our findings suggest that youth race, age, and parent mental health are each associated with youth physical health (i.e., BMI), confirming previous study findings that parental factors and demographic factors should be considered when exploring youth health outcomes.     

Orthogonal rotations to maximal agreement for two or more matrices of different column orders

Methods for orthogonal Procrustes rotation and orthogonal rotation to a maximal sum of inner products are examined for the case when the matrices involved have different numbers of columns. An inner product solution offered by Cliff is generalized to the case of more than two matrices. A nonrandom start for a Procrustes solution suggested by Green and Gower is shown to give better results than a random start. The Green-Gower Procrustes solution (with nonrandom start) is generalized to the case of more than two matrices. Simulation studies indicate that both the generalized inner product solution and the generalized Procrustes solution tend to attain their global optima within acceptable computation times. A simple procedure is offered for approximating simple structure for the rotated matrices without affecting either the Procrustes or the inner product criterion.The authors are obliged to Charles Lewis for helpful comments on a previous draft of this paper and to Frank Brokken for preparing a computer program that was used in this study.     

Understanding pregnant women's decision making concerning prenatal screening

OBJECTIVE: This study is aimed at enhancing understanding prenatal screening decision making through testing a hypothesized decision model based on decision theory and health behavior theory. DESIGN: We obtained questionnaires from 1,666 pregnant women who were offered prenatal screening for Down's syndrome. Path analysis (using LISREL) resulted in a final model with reasonable model fit, which was verified by split-sample cross-validation. MAIN OUTCOME MEASURES: These included perceived probability, perceived severity, attitude toward termination, response efficacy, attitude toward prenatal screening, subjective norm, child-related anxiety, and intention to undergo prenatal screening. RESULTS: Attitude toward termination of pregnancy, perceived test efficacy, and subjective norm regarding the desirability of having prenatal screening determined a woman's attitude toward having a prenatal test. Anxiety was influenced by perceived risk and perceived severity of having a child with Down's syndrome, and by subjective norm, but this appeared to be a weak predictor of intention to test. Pregnant women with a positive attitude toward prenatal screening, and who perceived a subjective norm in favor of undergoing prenatal screening, showed a greater intention to have prenatal screening done. CONCLUSION: These findings suggest that more attention should be paid toward the values and social context of pregnant women during the counseling process.     

The foreperiod effect revisited: conditioning as a basis for nonspecific preparation

The foreperiod (FP) is the interval between a warning stimulus and the imperative stimulus. It is a classical finding that both the duration and the intertrial variability of FP considerably affects response time. These effects are invariably attributed to the participant's state of nonspecific preparation at the moment the imperative stimulus is presented. In this article, we examined a proposal by Los, S. A. (1996) [On the origin of mixing costs: exploring information processing in pure and mixed blocks of trials. Acta Psychologica, 94, 145-188] that the real-time development of nonspecific preparation during FP relies on the same principle as trace conditioning. To this end, we adjusted the formal conditioning model developed by Machado, A. (1997) [Learning the temporal dynamics of behavior. Psychological Review, 104 (2), 241-265], and fitted this model to a representative data set we obtained from nine participants. Although the model accounted for only a moderate proportion of the variance, it accurately reproduced several key features of the data. We therefore concluded that the model is a promising first step toward a theory of nonspecific preparation.