Computing the COM from the COP in postural sway movements

A method is described for computing the centre of mass (COM) from empirical estimates of the centre of pressure (COP) obtained by means of a force platform. The method is based on a biomechanical model of sway movements in quiet standing, according to which the horizontal acceleration of the COM is approximately proportional to the COM–COP difference. The equations are solved by approximating the solution with best fitting spline functions. The implications for movement control are discussed.     

Are cognitive sex differences disappearing? Evidence from Spanish populations

Sex differences in cognitive abilities were determined using the norms from two standardizations of the Differential Aptitude Test (DAT) and the Primary Mental Abilities (PMA) conducted between 1979 and 1995 in Spain. The standardized sex differences (ds) were computed separately for the DAT and the PMA subscales. Males scored higher in the DAT subscales Verbal Reasoning, Numerical Ability, Spatial Relations and Mechanical Reasoning, as well as in the PMA subscales Numerical Ability and Mental Rotation. Females scored higher in Inductive Reasoning (PMA-R) in the 1979 and 1995 standardizations. Taken together, these data do not support the hypothesis that cognitive sex differences are disappearing: there are still some differences favoring females and still some differences favoring males.     

Uniqueness of three-mode factor models with sparse cores: The 3 × 3 × 3 case

Three-Mode Factor Analysis (3MFA) and PARAFAC are methods to describe three-way data. Both methods employ models with components for the three modes of a three-way array; the 3MFA model also uses a three-way core array for linking all components to each other. The use of the core array makes the 3MFA model more general than the PARAFAC model (thus allowing a better fit), but also more complicated. Moreover, in the 3MFA model the components are not uniquely determined, and it seems hard to choose among all possible solutions. A particularly interesting feature of the PARAFAC model is that it does give unique components. The present paper introduces a class of 3MFA models in between 3MFA and PARAFAC that share the good properties of the 3MFA model and the PARAFAC model: They fit (almost) as well as the 3MFA model, they are relatively simple and they have the same uniqueness properties as the PARAFAC model.This research has been made possible by a fellowship from the Royal Netherlands Academy of Arts and Sciences to the first author. Part of this research has been presented at the first conference on ThRee-way methods In Chemistry (TRIC), a meeting of Psychometrics and Chemometrics, Epe, The Netherlands, August 1993. The authors are obliged to Age Smilde for stimulating this research, and two anonymous reviewers for many helpful suggestions.     

Transforming three-way arrays to maximal simplicity

Transforming the core array in Tucker three-way component analysis to simplicity is an intriguing way of revealing structures in between standard Tucker three-way PCA, where the core array is unconstrained, and CANDECOMP/PARAFAC, where the core array has a generalized diagonal form. For certain classes of arrays, transformations to simplicity, that is, transformations that produce a large number of zeros, can be obtained explicitly by solving sets of linear equations. The present paper extends these results. First, a method is offered to simplifyJ ×J × 2 arrays. Next, it is shown that the transformation that simplifies anI ×J ×K array can be used to also simplify the (complementary) arrays of order (JK −I) ×J ×K, of orderI × (IK −J) ×K and of orderI ×J × (IJ −K). Finally, the question of what constitutes the maximal simplicity for arrays (the maximal number of zero elements) will be considered. It is shown that cases of extreme simplicity, considered in the past, are, in fact, cases of maximal simplicity.     

Compression and Expansion of Circadian Rhythm in Mice Under Long and Short Photoperiods

Although the functional aspects of synchronization of the circadian pacemaker by environmental light have been extensively studied, few studies have provided systematic information about the temporal organization of behavior under light-dark cycles with varying proportions of light and darkness. In the present study, the running-wheel activity profiles of mice were investigated under short, medium, and long photoperiods. The results clearly indicated that the temporal distribution of locomotor activity in mice is modulated by photoperiod. The activity profile was compressed under long photoperiods and expanded under short photoperiods. Although negative masking by light and alterations in the state of dark adaptation may have partially accounted for the phenomenon, the major mechanism seemed to be a compression and expansion of the circadian pacemaker's cycle, as expressed in the compression and expansion of the photic phase-response curve.     

Reinforcement of wheel running in BALB/c mice: role of motor activity and endogenous opioids

The authors investigated the effect of the opioid antagonist naloxone on wheel-running behavior in Balb/c mice. Naloxone delayed the acquisition of wheel-running behavior, but did not reduce the expression of this behavior once acquired. Delayed acquisition was not likely a result of reduced locomotor activity, as naloxone-treated mice did not exhibit reduced wheel running after the behavior was acquired, and they performed normally on the rotarod test. However, naloxone-blocked conditioned place preference for a novel compartment paired previously with wheel running, suggesting that naloxone may delay wheel-running acquisition by blocking the rewarding or reinforcing effects of the behavior. These results suggest that the endogenous opioid system mediates the initial reinforcing effects of wheel running that are important in acquisition of the behavior.     

Evaluation of Siddha Samadhi Yoga for anxiety and depression symptoms: a preliminary study

Siddha Samadhi Yoga is a program in which meditation is associated with pranayama (breathing exercises). 22 volunteers with anxiety complaints (M age = 42.8 yr., SD = 10.3) were assigned to two groups: 14 attended the yoga group, and 8 attended a waiting-list or control group. They were evaluated before the intervention and 1 month after it on the State-Trait Anxiety Inventory, the Beck Depression Inventory, Tension Feelings Self-evaluation Scales, and the Well-being Self-evaluation Scales. A significant reduction in scores on anxiety, depression, and tension was found in yoga group, as well as an increase in well-being in comparison with the control group.