Effects of varied-stimulus exposure on overpredictions of pain and behavioural performance in low back pain patients

The main objective of the present study was to investigate the benefits of exposure to a variety of movements versus exposure to the same movements on overprediction of pain and behavioural performance on a final behavioural test in a sample of chronic low back pain (CLBP) patients. Eighty-four CLBP patients were requested to perform four behavioural tests. Patients were assigned to two experimental conditions. The final behavioural test was the same for all patients. The first three behavioural tests consisted of three different movements in condition 1 and of three times the same movement in condition 2. During each behavioural test, baseline pain, expected pain and experienced pain were recorded. Furthermore, the peak torque and the variability of the produced muscle strength during the final behavioural test were assessed. Replicating and extending previous research, we found that patients overpredicted pain during a threatening behavioural test. Furthermore, pain-related fear and pain catastrophizing showed to be unique predictors of the peak torque of the final behavioural test. No support was found for our hypothesis that varied exposure facilitates generalization of exposure effects. Possible reasons for the failure to find an advantageous effect of varied-stimulus exposure and ideas for future research are discussed.     

A simple and sensitive method to measure timing accuracy

Timing accuracy in presenting experimental stimuli (visual information on a PC or on a TV) and responding (keyboard presses and mouse signals) is of importance in several experimental paradigms. In this article, a simple system for measuring timing accuracy is described. The system uses two PCs (at least Pentium II, 200 MHz), a photocell, and an amplifier. No additional boards and timing hardware are needed. The first PC, a SlavePC, monitors the keyboard presses or mouse signals from the PC under test and uses a photocell that is placed in front of the screen to detect the appearance of visual stimuli on the display. The software consists of a small program running on the SlavePC. The SlavePC is connected through a serial line with a second PC. This MasterPC controls the SlavePC through an ActiveX control, which is used in a Visual Basic program. The accuracy of our system was investigated by using a similar setup of a SlavePC and a MasterPC to generate pulses and by using a pulse generator card. These tests revealed that our system has a 0.01-msec accuracy. As an illustration, the reaction time accuracy of INQUISIT for a few applications was tested using our system. It was found that in those applications that we investigated, INQUISIT measures reaction times from keyboard presses with millisecond accuracy.     

Intraindividual variability in infant behavior.

Longitudinal observational data of infant crying, fretting/fussing, and smiling and the time spent in physical contact with the mother were used in a study on behavioral variability. The infants were followed weekly for a 15-month period. Evidence was found of an important intraindividual variability in the studied behaviors, specifically between the ages of 0 and 5 months, 5 and 10 months, but not between 10 and 15 months. Results are discussed and analyzed in the light of earlier literature. The possible functions and the factors underlying variability in development as well as its methodological implications are discussed.     

The coupling of head,reach and grasp movement in nine months old infant prehension

In 9-month-old-infants adjustments in the reaching pattern to sudden changes in object location were examined. An attractive ball was presented to the infants at their midline and on some trials (perturbation trials) the ball suddenly changed position 15 cm to the right or left during the reach. For the perturbed trials the movement times approximately doubled compared to the control trials and significantly fewer balls were grasped. The results indicate that infants need to finish the first movement before being able to redirect the reach to a new destination. The correlation between the latency of the head and hand adjustment to the perturbation were 0.85 and 0.78 for movements to the left and to the right, respectively, indicating a tight coupling. The time between the start of the perturbation and peak velocity (TPPV) was significantly shorter for the head movement than for the hand movement, indicating that the head is leading the hand.     

A least squares algorithm for fitting additive trees to proximity data

A least squares algorithm for fitting additive trees to proximity data is described. The algorithm uses a penalty function to enforce the four point condition on the estimated path length distances. The algorithm is evaluated in a small Monte Carlo study. Finally, an illustrative application is presented.The author is Aspirant of the Belgian Nationaal Fonds voor Wetenschappelijk Onderzoek. The author is indebted to Professor J. Hoste for providing computer facilities at the Institute of Nuclear Sciences at Ghent.     

A Mixed Model to Disentangle Variance and Serial Autocorrelation in Affective Instability Using Ecological Momentary Assessment Data

Affective instability, the tendency to experience emotions that fluctuate frequently and intensively over time, is a core feature of several mental disorders including borderline personality disorder. Currently, affect is often measured with Ecological Momentary Assessment protocols, which yield the possibility to quantify the instability of affect over time. A number of linear mixed models are proposed to examine (diagnostic) group differences in affective instability. The models contribute to the existing literature by estimating simultaneously both the variance and serial dependency component of affective instability when observations are unequally spaced in time with the serial autocorrelation (or emotional inertia) declining as a function of the time interval between observations. In addition, the models can eliminate systematic trends, take between subject differences into account and test for (diagnostic) group differences in serial autocorrelation, short-term as well as long-term affective variability. The usefulness of the models is illustrated in a study on diagnostic group differences in affective instability in the domain of eating disorders. Limitations of the model are that they pertain to group (and not individual) differences and do not focus explicitly on circadian rhythms or cycles in affect.     

The Dynamics of General Developmental Mechanisms: From Piaget and Vygotsky to Dynamic Systems Models

Dynamic systems theory conceives of development as a self-organizational process. Both complexity and order emerge as a product of elementary principles of interaction between components involved in the developmental process. This article presents a dynamic systems model based on a general dual developmental mechanism, adapted from Piaget and Vygotsky. The mechanism consists of a conservative force, further strengthening the already-consolidated level, and a progressive force, consolidating internal contents and procedures at more advanced levels. It is argued that this dual mechanism constitutes one of the few basic laws of learning and change, and is comparable to the laws of effect and of contiguity. Simulation studies suggest that this dual mechanism explains self-organization in developmental paths, including the emergence of discrete jumps from one equilibrium level to another, S-shaped growth, and the occurrence of co-existing levels.     

Contribution of content, context, and process to understanding openness to organizational change: two experimental simulation studies

The authors examined the contribution of the content, context, and process of organizational transformation to employees' openness to change. The authors predicted that 5 factors would have a positive effect on openness to change: (a) threatening character of organizational change (content related), (b) trust in executive management (context related), (c) trust in the supervisor (context related), (d) history of change (context related), and (e) participation in the change effort (process related). The authors tested their hypotheses in 2 separate studies (N = 828 and N = 835) using an experimental simulation strategy. The first study crossed 4 variables in a completely randomized 2 x 2 x 2 x 2 factorial design. Results showed significant main effects for content, context, and process but no significant interaction effects. A second study, with a completely randomized 2 x 2 factorial design, crossed two context variables. Results showed a significant main and an interaction effect: Openness to change decreased dramatically only when history of change and trust in executive management were low.