Statistical Significance of the Contribution of Variables to the PCA solution: An Alternative Permutation Strategy

In this paper, the statistical significance of the contribution of variables to the principal components in principal components analysis (PCA) is assessed nonparametrically by the use of permutation tests. We compare a new strategy to a strategy used in previous research consisting of permuting the columns (variables) of a data matrix independently and concurrently, thus destroying the entire correlational structure of the data. This strategy is considered appropriate for assessing the significance of the PCA solution as a whole, but is not suitable for assessing the significance of the contribution of single variables. Alternatively, we propose a strategy involving permutation of one variable at a time, while keeping the other variables fixed. We compare the two approaches in a simulation study, considering proportions of Type I and Type II error. We use two corrections for multiple testing: the Bonferroni correction and controlling the False Discovery Rate (FDR). To assess the significance of the variance accounted for by the variables, permuting one variable at a time, combined with FDR correction, yields the most favorable results. This optimal strategy is applied to an empirical data set, and results are compared with bootstrap confidence intervals.     

The shared leadership process in decision-making teams

The present study examined the process of shared leadership in 45 ad hoc decision-making teams. Each team member's leadership behavior (n = 180) was assessed by behaviorally coding videotapes of the teams' discussions. The within-team patterns of leadership behavior were examined using cluster analysis. Results indicated that the likelihood of a team experiencing a full range of leadership behavior increased to the extent that multiple team members shared leadership, and that teams with shared leadership experienced less conflict, greater consensus, and higher intragroup trust and cohesion than teams without shared leadership. This study supports previous findings that shared leadership contributes to overall team functioning, and begins to delineate the extent to which team members may naturally share leadership.     

Violence Exposure Mediates the Relation Between Callous-Unemotional Traits and Offending Patterns in Adolescents

The link between callous-unemotional (CU) traits in youth and delinquent, aggressive and violent behavior is well-replicated in the literature. However, the mediating effects of violence exposure on this relationship are unclear. The current study addresses this important gap in the literature with a sample of 88 detained, primarily ethnic minority adolescent boys (M age?=?15.57; SD?=?1.28). Results indicate that exposure to violence fully mediated the relationship between CU traits and violent delinquency, and this pattern of mediation was accounted for by exposure to witnessed violence, but not direct violent victimization. Secondly, exposure to violence, both direct and witnessed forms, also mediated the relationship between CU traits and drug delinquency. These findings suggest that (a) the well-established link between CU traits and violence may be attributed to high rates of witnessed violence among this subpopulation, and (b) specific types of violence exposure may be important for predicting the offending patterns of youth high on CU traits. Theoretical and practical implications are discussed.     

GazeAlyze: a MATLAB toolbox for the analysis of eye movement data

This article presents GazeAlyze, a software package, written as a MATLAB (MathWorks Inc., Natick, MA) toolbox developed for the analysis of eye movement data. GazeAlyze was developed for the batch processing of multiple data files and was designed as a framework with extendable modules. GazeAlyze encompasses the main functions of the entire processing queue of eye movement data to static visual stimuli. This includes detecting and filtering artifacts, detecting events, generating regions of interest, generating spread sheets for further statistical analysis, and providing methods for the visualization of results, such as path plots and fixation heat maps. All functions can be controlled through graphical user interfaces. GazeAlyze includes functions for correcting eye movement data for the displacement of the head relative to the camera after calibration in fixed head mounts. The preprocessing and event detection methods in GazeAlyze are based on the software ILAB 3.6.8 Gitelman (Behav Res Methods Instrum Comput 34(4), 605-612, 2002). GazeAlyze is distributed free of charge under the terms of the GNU public license and allows code modifications to be made so that the program's performance can be adjusted according to a user's scientific requirements.     

Plasticity of prospective memory through a familiarization intervention in old adults

Younger adults consistently outperform older adults in laboratory prospective memory tasks. This study examines the effectiveness of an intervention that familiarizes older adults with the sequence of ongoing events to compensate their reduced prospective memory performance. We compared performance and electrophysiological measures of an intervention group (N = 20, 69-83 years) receiving a familiarization intervention to an individually matched control group (N = 20). As ongoing activity a 2-back working memory task was administered. Neural correlates were studied using event related potentials (ERPs) and source localization (standardized low-resolution brain electromagnetic tomography). Behavioural data showed faster reaction times in correct prospective trials and fewer prospective false alarms in the familiarization intervention group. ERP analyses displayed differential patterns for the two groups and source localization measures distinctively presented group differences in prospective memory trials with the control group recruiting more resources for a successful prospective memory performance. Together our data support the hypothesis that the familiarity with the sequence of ongoing events increases prospective memory performance and that this might be based on a higher efficiency of attentional monitoring resources and evaluation processes in the intervention group.     

Hand preference and its flexibility according to the position of the object: a study in cercopithecines examining spontaneous behaviour and an experimental task (the Bishop QHP task)

The extant literature on manual laterality in non-human primates is inconclusive, plagued by inconsistent or contradictory findings and by disturbing methodological issues (e.g. uncontrolled influential factors, comparability issues). The present study examined hand preference and its flexibility in 15 red-capped mangabeys (C. t. torquatus) and 13 Campbell's monkeys (C. c. campbelli), two species that differ in their degree of arboreality. We investigated the influence of the spatial position of the object on hand preference for reaching. We considered spontaneous behaviour (reaching for food during daily feeding) and an experimental task: the QHP task. The QHP is a task that is used in humans. This is a simple reaching task that involves high spatial constraints on hand use. In our study, the subject had to reach for items that were placed on a semi-circle in front of it on five positions, including in the centre position, in the ipsilateral space and in the contralateral space. We assessed hand preference for reaching in front (baseline condition), and we examined how this preference changed when reaching in lateral positions. For reaching in front, about half of the subjects were lateralized and no group-level bias occurred, for both spontaneous and experimental conditions. When considering reaching in the lateral positions, we observed that the position of the object influenced hand use: individuals used the hand that was closest to the object. The results are discussed in relation to previous findings in humans and in non-human primates and regarding theories on handedness and flexibility of hand preference.     

Canine responses to familiar and unfamiliar humans

Dogs were observed during controlled approaches by their owners and by strangers. Significant differences between the dogs' responses to their owners and their responses to strangers were found. These results supported the popular belief that dogs respond differently to different persons, and not merely to different situations in which persons are usually encountered.