Coupling online control and inhibitory systems in children with Developmental Coordination Disorder: Goal-directed reaching

For children with Developmental Coordination Disorder (DCD), the real-time coupling between frontal executive function and online motor control has not been explored despite reported deficits in each domain. The aim of the present study was to investigate how children with DCD enlist online control under task constraints that compel the need for inhibitory control. A total of 129 school children were sampled from mainstream primary schools. Forty-two children who met research criteria for DCD were compared with 87 typically developing controls on a modified double-jump reaching task. Children within each skill group were divided into three age bands: younger (6–7 years), mid-aged (8–9), and older (10–12). Online control was compared between groups as a function of trial type (non-jump, jump, anti-jump). Overall, results showed that while movement times were similar between skill groups under simple task constraints (non-jump), on perturbation (or jump) trials the DCD group were significantly slower than controls and corrected trajectories later. Critically, the DCD group was further disadvantaged by anti-jump trials where inhibitory control was required; however, this effect reduced with age. While coupling online control and executive systems is not well developed in younger and mid-aged children, there is evidence of age-appropriate coupling in older children. Longitudinal data are needed to clarify this intriguing finding. The theoretical and applied implications of these results are discussed.     

Robust rigid registration of retinal angiograms through optimization

Retinal fundus photographs are employed as standard diagnostic tools in ophthalmology. Serial photographs of the flow of fluorescein and indocyanine green (ICG) dye are used to determine the areas of the retinal lesions. For objective measurements of features, the registration of the images is a necessity. In this paper, we employ optimization techniques for registration with the help of 2-parameter translational motion model of retinal angiograms, based on non-linear pre-processing (Wiener filtering and morphological gradient) and computation of the similarity criteria for the alignment of the two gradient images for any given rigid transformation. The optimization methods are effectively employed to minimize the similarity criterion.

The presence of noise, the variations in the background and the temporal variation of the fluorescence level pose serious problems in obtaining a robust registration of the retinal images. Moreover, local search strategies are not robust in the case of ICG angiograms, even if one uses a multiresolution approach.

The present work makes a systematic comparison of different optimization techniques, namely the minimization method derived from the optical flow formulation, the Nelder-Mead local search and the HCIAC ant colony metaheuristic, each optimizing a similarity criterion for the gradient images. The impact of the resolution and median filtering of gradient image is studied and the robustness of the approaches is tested through experimental studies, performed on macular fluorescein and ICG angiographies.

Our proposed optimization techniques have shown interesting results especially for high resolution difficult registration problems. Moreover, this approach seems promising for affine (6-parameter motion model) or elastical registrations.     

Which constructs can predict emotional exhaustion in a working population? A study into its determinants

The main objective of this study was to examine the psychosocial stress model developed by Taylor and Aspinwall with emotional exhaustion as the outcome variable. Respondents, 409 men and 346 women, who had a paid job for at least 20 hours per week, completed questionnaires concerning demographic variables, personality, temperament, work pressure, workload, perceived social support, appraisal, coping, and emotional exhaustion. Structural equation analyses provided only partial support for the validity of the model. First, on theoretical and statistical grounds, one more path linking external resources to social support was added. Second, contrary to expectations, coping styles did not predict emotional exhaustion. To conclude, when coping is measured retrospectively, it does not add to our understanding of emotional exhaustion. It is suggested that future studies should be longitudinal and include objective measures of stressors and psychosocial health outcomes in addition to self‐reports. Copyright © 2007 John Wiley & Sons, Ltd.     

Working‐correlation‐structure identification in generalized estimating equations

Selecting an appropriate working correlation structure is pertinent to clustered data analysis using generalized estimating equations (GEE) because an inappropriate choice will lead to inefficient parameter estimation. We investigate the well‐known criterion of QIC for selecting a working correlation structure, and have found that performance of the QIC is deteriorated by a term that is theoretically independent of the correlation structures but has to be estimated with an error. This leads us to propose a correlation information criterion (CIC) that substantially improves the QIC performance. Extensive simulation studies indicate that the CIC has remarkable improvement in selecting the correct correlation structures. We also illustrate our findings using a data set from the Madras Longitudinal Schizophrenia Study. Copyright © 2008 John Wiley & Sons, Ltd.     

Three-dimensional biomechanical properties of the human rectum evaluated with magnetic resonance imaging

A method to evaluate the three-dimensional (3-D) geometry of the human gastrointestinal wall may be valuable for understanding tissue biomechanics, mechano-sensation and function. In this paper we present a magnetic resonance imaging (MRI) based method to determine rectal geometry and validation of data obtained in three volunteers. A specially designed rectal bag was filled in a stepwise manner while MRI and bag pressure were recorded. 3-D models of curvatures, radii of curvature, tension and stress were generated and the circumferential and longitudinal strains were calculated. The computed bag volumes corresponded to the infused volumes. A pronounced bag elongation and decrease in wall thickness was observed during the bag filling. The spatial distributions of the biomechanical parameters were distinctly different between individuals and non-homogeneous throughout the rectal wall due to its complex geometry. The average tension and stress increased as a function of infused volume and circumferential strain. The present study provides a method for characterizing the complex in vivo 3-D geometry of the human rectum. The non-homogenous spatial curvature distribution suggests that simple estimates of tension based on pressure and volume do not reflect the true 3-D biomechanical properties of the rectum.     

数学障碍儿童的工作记忆研究

目的：探讨数学障碍儿童的工作记忆状况。方法：采用智力测睑、成就测验、教师提名、学业成绩相结合的综合标准甑选数学障碍儿童，在长沙市三所小学随机选取4～6年级共12个班，从中抽取24名数学障碍儿童和24名学习正常儿童。采用工作记忆成套测验对2组被试进行评估。结果：数学障碍组除空间排序、空间后退以及数字划销3个分测验外，在工作记忆成套测验其它各分测验及各维度上的成绩均显著低于学习正常组（P〈0．001～0．05）。结论：数学障碍儿童工作记忆存在普遍缺陷。     

A model for estimating the potential costs and savings of osteoporosis prevention strategies

A model was developed which estimates the costs of osteoporosis risk evaluation and treatment, and the resulting savings in terms of reduced fracture frequency, for the adult female population of the United States. In the absence of treatment, the model predicts 1.44 million fractures will occur annually from non-violent causes. Treatment of all women beginning at age 50 with an agent that slows bone loss by 50% would reduce the number of these fractures by 0.59 million. Selective treatment of the 47% of women at the greatest fracture risk would reduce the number of fractures by 0.45 million, but would only cost 47% as much as treating all women. Additional data are required before the model can be used to evaluate specific treatment regimens. However, it appears that selective treatment of those at highest risk would yield the greatest benefit to cost ratio, if only benefits related to reduced fracture frequency are considered.     

Stochastic models for geriatric in-patient behaviour

Departments of geriatric medicine engage in two distinct formsof clinical activity: acute/rehabilitative and long-stay care.These are organizationally distinct and have very differentresource needs. Current hospital planning models, however, assumethat patients all move through the system at the same rate,thereby ignoring this effect of inherent heterogeneity in patientbehaviour. The present paper describes the movement of patientsthrough geriatric hospitals by a two-stage continuous-time Markovmodel, where the stages represent acute/rehabilitative and long-staypatients respectively. Patients are initially admitted to thefirst stage, from which they may depart from the system, bydeath or discharge, or move into the second stage, from whichthey eventually depart by death or discharge (unlikely). Admissionsare modelled in two ways: either as replacements for departuresor as a Poisson stream. Expressions for the distribution andmovement of numbers of patients are derived and evaluated fordata from a number of hospitals. Such an approach has the advantage,over previous crude models, of taking into account differenttypes of patients and introducing variability, thus making itpossible to extract variances as well as means of numbers ofgeriatric patients requiring hospital care.