Changes in the relationship between movement velocity and movement distance in primary focal hand dystonia

The authors examined the relationship between movement velocity and distance and the associated muscle activation patterns in 18 individuals with focal hand dystonia (FHD) compared with a control group of 18 individuals with no known neuromuscular condition. Participants performed targeted voluntary wrist and elbow flexion movements as fast as possible across 5 movement distances. Individuals with FHD were slower than controls across all distances, and this difference was accentuated for longer movements. Muscle activation patterns were triphasic in the majority of individuals with FHD, and muscle activation scaled with distance in a similar manner to controls. Cocontraction did not explain movement slowing in individuals with dystonia, but there was a trend toward underactivation of the 1st agonist burst in the dystonic group. The authors concluded that slowness is a consistent feature of voluntary movement in FHD and is present even in the absence of dystonic posturing. Underactivation of the 1st agonist burst appears to be the most likely reason to explain slowing.     

Current Directions in Mediation Analysis

ABSTRACT— Mediating variables continue to play an important role in psychological theory and research. A mediating variable transmits the effect of an antecedent variable on to a dependent variable, thereby providing more detailed understanding of relations among variables. Methods to assess mediation have been an active area of research for the last two decades. This paper describes the current state of methods to investigate mediating variables.     

R2 effect-size measures for mediation analysis

R ² effect-size measures are presented to assess variance accounted for in mediation models. The measures offer a means to evaluate both component paths and the overall mediated effect in mediation models. Statistical simulation results indicate acceptable bias across varying parameter and sample-size combinations. The measures are applied to a real-world example using data from a team-based health promotion program to improve the nutrition and exercise habits of firefighters. SAS and SPSS computer code are also provided for researchers to compute the measures in their own data.     

Distribution of the product confidence limits for the indirect effect: Program PRODCLIN

This article describes a program, PRODCLIN (distribution of the PRODuct Confidence Limits for INdirect effects), written for SAS, SPSS, and R, that computes confidence limits for the product of two normal random variables. The program is important because it can be used to obtain more accurate confidence limits for the indirect effect, as demonstrated in several recent articles (MacKinnon, Lockwood, & Williams, 2004; Pituch, Whittaker, & Stapleton, 2005). Tests of the significance of and confidence limits for indirect effects based on the distribution of the product method have more accurate Type I error rates and more power than other, more commonly used tests. Values for the two paths involved in the indirect effect and their standard errors are entered in the PRODCLIN program, and distribution of the product confidence limits are computed. Several examples are used to illustrate the PRODCLIN program. The PRODCLIN programs in rich text format may be downloaded from www.psychonomic.org/archive.     

The criminal and personality profile of patients with schizophrenia and comorbid psychopathic traits

Sixty-one male forensic patients who met the DSM-IV criteria for schizophrenia were categorised into high and low psychopathic trait groups using the Psychopathy Checklist: Screening Version. The groups were compared on their criminal history, symptom profile, personality style, risk scores and subsequent institutional violence. Patients with high scores on the PCL:SV had a greater number of previous convictions and were more likely to have a family history of criminality. The high psychopathy-scoring group had higher levels of Positive and Negative Syndrome Scale grandiose and hostile symptomatology, and higher scores on trait impulsivity and aggression. They also had a more coercive, less compliant interpersonal style than the low-psychopathy scoring group. The high-psychopathy scoring group were more likely to be involved in institutional aggression and had higher levels of risk for violence. Patients with schizophrenia and high levels of comorbid psychopathy have a distinctive interpersonal style that may contribute to their greater risk of disruptive institutional behaviour.     

Statistical properties of four effect-size measures for mediation models

This project examined the performance of classical and Bayesian estimators of four effect size measures for the indirect effect in a single-mediator model and a two-mediator model. Compared to the proportion and ratio mediation effect sizes, standardized mediation effect-size measures were relatively unbiased and efficient in the single-mediator model and the two-mediator model. Percentile and bias-corrected bootstrap interval estimates of ab/s _Y , and ab(s _X )/s _Y in the single-mediator model outperformed interval estimates of the proportion and ratio effect sizes in terms of power, Type I error rate, coverage, imbalance, and interval width. For the two-mediator model, standardized effect-size measures were superior to the proportion and ratio effect-size measures. Furthermore, it was found that Bayesian point and interval summaries of posterior distributions of standardized effect-size measures reduced excessive relative bias for certain parameter combinations. The standardized effect-size measures are the best effect-size measures for quantifying mediated effects.     

Coping and negative appraisal as mediators between control beliefs and psychological symptoms in children of divorce

Examined control beliefs of children of divorce as predictors of their coping, negative appraisals for stressful events, and mental health problems. We tested whether coping and negative appraisal for stressful events mediated the relations between multiple dimensions of control beliefs and mental health problems. Different dimensions of control beliefs were related to different aspects of coping and negative stress appraisal. Internal control beliefs for positive events were related to both active and avoidant coping. Unknown control beliefs for positive events were related to higher active coping and higher negative appraisal. Unknown control beliefs for negative events were related to higher avoidant coping. In addition, evidence for mediation was found such that the effect of unknown control beliefs for positive events on mental health problems was mediated by negative appraisal. Implications and directions for further research are discussed.     

Enhancing Children's Spatial and Numerical Skills through a Dynamic Spatial Approach to Early Geometry Instruction: Effects of a 32-Week Intervention

This study describes the implementation and effects of a 32-week teacher-led spatial reasoning intervention in K–2 classrooms. The intervention targeted spatial visualization skills as an integrated feature of regular mathematics instruction. Compared to an active control group, children in the spatial intervention demonstrated gains in spatial language, visual-spatial reasoning, 2D mental rotation, and symbolic number comparison. Overall, the findings highlight the potential significance of attending to and developing young children's spatial thinking as part of early mathematics instruction.     

Process dissociation of sight vocabulary and phonetic decoding in reading: a new perspective on surface and phonological dyslexias

Recent research on developmental dyslexia has suggested a phonological core deficit hypothesis (e.g., Manis, Seidenberg, Doi, McBride-Chang, & Peterson, 1996; Stanovich, Siegel, & Gottardo, 1997) whereby pure cases of developmental phonological dyslexia (dysfunctional phonetic decoding processing but normal sight vocabulary processing) can exist, but pure cases of developmental surface dyslexia (dysfunctional sight vocabulary processing but normal phonetic decoding processing) should not. By applying Jacoby's (1991) and Lindsay and Jacoby's (1994) process dissociation procedure to the reading of regular and exception words, we present a method that serves to estimate readers' reliance on sight vocabulary and phonetic decoding during real word recognition. These reliance estimates are then used in Castles and Coltheart's (1993) regression-based approach to identify normal readers and developmental dyslexics. This new method: (1) allows one to explore normal reading acquisition and both the delay and deviance accounts of developmental dyslexia, (2) provides an alternative to matching dyslexics to both chronological-age and reading-age control groups, and (3) uses only real words. We present evidence that pure cases of developmental surface dyslexia can be obtained with both Castles and Coltheart's measure as well as our own, and that developmental surface dyslexia is not simply a delayed reading deficit. The theoretical importance and utility of estimates of reliance on sight vocabulary and phonetic decoding is discussed.