Deriving exact predictions from the cascade model.

Discusses J. L. McClelland's (see record 1979-32860-001) cascade model and demonstrates that the model does not have a well-defined RT distribution function because it always predicts a nonzero probability that a response will never occur. By conditioning on the event that a response does occur, RT density and distribution functions are derived, thus allowing most RT statistics to be computed directly and eliminating the need for computer simulations. Using these results, an investigation of the model reveals that (a) it predicts mean RT additivity in most cases of pure insertion or selective influence, (b) it predicts only a very small increase in standard deviations as mean RT increases, and (c) it does not mimic the distribution of discrete-stage models that have a serial stage with an exponentially disturbed duration. (12 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Deriving a preference-based single index from the UK SF-36 Health Survey

This article presents the results of a study to derive a preference-based single index from the SF-36. The study was an attempt to reconcile a profile health status measure, the SF-36, with the "quality adjusted life years" approach. The study undertook a parsimonious restructuring of the SF-36 using explicit criteria to form the SF-6D health state classification. A sample of multidimensional health states defined by this classification were valued by a convenience sample of health professionals, managers, and patients, who responded to a set of visual analogue scale ratings and standard gamble questions, with highly complete and consistent answers. Statistical models were estimated to predict single index scores for all 9000 health states defined by the new classification. The resultant algorithms can be applied to existing SF-36 data sets and used in the assessment of the cost-effectiveness of health technologies. This preliminary work forms the basis of a larger study currently being undertaken in the UK.     

Deriving reaction mechanisms from kinetic spectroscopy. Application to late rhodopsin intermediates

A general algebraic approach to the kinetic analysis of time-dependent absorption data is presented that allows the calculation of possible kinetic schemes. The kinetic matrices of all possible reaction mechanisms are calculated from experimental eigenvalues and eigenvectors derived from the decay constants and amplitude spectra (b-spectra) of the global exponential fit to the time-dependence of the absorption data. The eigenvalues are directly related to the decay constants, and the eigenvectors are obtained by decomposing the b-spectra into spectral components representing the intermediates. The analysis method is applied to the late intermediates (lumi, meta I, meta I-380, and meta II) of the rhodopsin photoreaction. The b-spectra are decomposed into lumi, meta I, meta-380, and rhodopsin spectra. The meta-380 component is partitioned into isospectral meta I-380 and meta II components based on physical criteria. The calculated kinetic matrices yield a number of reaction mechanisms (linear scheme with back reactions, branched schemes with equilibrium steps, and a variety of square models) consistent with the photolysis data at 25 degrees C. The problems associated with isospectral intermediates (meta I-380 and meta II) are treated successfully with this method.     

Assumptions in making causal inferences from part correlations, partal correlations, and partial regression coefficients.

Given a linear model and that X is antecedent to Y, antecedent variables are usually controlled to remove spurious association. The assumptions in various measures of the "influence" of X on Y after partialing antecedent variables are described. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Striate cortex extracts higher-order spatial correlations from visual textures

Spatial correlations define the statistical structure of any visual image. Two-point correlations inform the visual system about the spatial frequency content of an image. Higher-order correlations can capture salient features such as object contours. We studied "isodipole" texture discrimination in V1 to determine if higher-order spatial correlations can be extracted by early stages of cortical processing. We made epicortical, local field potential, and single-cell recordings of responses elicited by isodipole texture interchange in anesthetized monkeys. Our studies demonstrate that single neurons in V1 can signal the presence of higher-order spatial correlations in visual textures. This places a computational mechanism, which may be essential for form vision at the earliest stage of cortical processing.     

Deriving childhood temperament measures from emotion-eliciting behavioral episodes: Scale construction and initial validation.

The authors describe the development and initial validation of a home-based version of the Laboratory Temperament Assessment Battery (Lab-TAB), which was designed to assess childhood temperament with a comprehensive series of emotion-eliciting behavioral episodes. This article provides researchers with general guidelines for assessing specific behaviors using the Lab-TAB and for forming behavioral composites that correspond to commonly researched temperament dimensions. We used mother ratings and independent postvisit observer ratings to provide validity evidence in a community sample of 4.5-year-old children. 12 Lab-TAB behavioral episodes were employed, yielding 24 within-episode temperament components that collapsed into 9 higher level composites (Anger, Sadness, Fear, Shyness, Positive Expression, Approach, Active Engagement, Persistence, and Inhibitory Control). These dimensions of temperament are similar to those found in questionnaire-based assessments. Correlations among the 9 composites were low to moderate, suggesting relative independence. As expected, agreement between Lab-TAB measures and postvisit observer ratings was stronger than agreement between the Lab-TAB and mother questionnaire. However, for Active Engagement and Shyness, mother ratings did predict child behavior in the Lab-TAB quite well. Findings demonstrate the feasibility of emotion-eliciting temperament assessment methodologies, suggest appropriate methods for data aggregation into trait-level constructs and set some expectations for associations between Lab-TAB dimensions and the degree of cross-method convergence between the Lab-TAB and other commonly used temperament assessments. (PsycINFO Database Record (c) 2011 APA, all rights reserved)