Regular use of illegal drugs is suspected to cause cognitive impairments. Two substances have received heightened attention: 3,4-methylenedioxymethamphetamine (MDMA or ‘ecstasy’) and δ-9-tetrahydrocannabinol (THC or ‘cannabis’). Preclinical evidence, as well as human studies examining regular ecstasy consumers, indicated that ecstasy use may have negative effects on learning, verbal memory and complex attentional functions. Cannabis has also been linked to symptoms of inattention and deficits in learning and memory. Most of the published studies in this field of research recruited participants by means of newspaper advertisements or by using word-of-mouth strategies. Because participants were usually aware that their drug use was critical to the research design, this awareness may have caused selection bias or created expectation effects. Focussing on attention and memory, this study aimed to assess cognitive functioning in a community-based representative sample that was derived from a large-scale epidemiological study. Available data concerning drug use history allowed sampling of subjects with varying degrees of lifetime drug experiences. Cognitive functioning was examined in 284 young participants, between 22 and 34 years. In general, their lifetime drug experience was moderate. Participants completed a neuropsychological test battery, including measures for verbal learning, memory and various attentional functions. Linear regression analysis was performed to investigate the relationship between cognitive functioning and lifetime experience of drug use. Ecstasy and cannabis use were significantly related to poorer episodic memory function in a dose-related manner. For attentional measures, decrements of small effect sizes were found. Error measures in tonic and phasic alertness tasks, selective attention task and vigilance showed small but significant effects, suggesting a stronger tendency to experience lapses of attention. No indication for differences in reaction time was found. The results are consistent with decrements of memory and attentional performance described in previous studies. These effects are relatively small; however, it must be kept in mind that this study focussed on assessing young adults with moderate drug use from a population-based study.

Le travail de nuit est associé avec plusieurs problèmes de santé. Le désalignement entre la phase circadienne et le cycle éveil-sommeil cause une désynchronie interne considérée comme la principale source de ces problèmes. L’ajustement circadien au travail de nuit est proposé comme contremesure. Normalement, l’ajustement circadien complet n’est pas recommandé puisqu’il engendre un désalignement circadien lors du retour à l’horaire de jour, causant des changements de phase répétés et la désynchronie interne. L’ajustement circadien partiel est alors proposé comme compromis afin de stabiliser les rythmes circadiens des travailleurs de nuit. Cependant, l’ampleur de l’ajustement circadien partiel nécessaire à l’amélioration du sommeil et de la vigilance demeure vague. Les ajustements partiels obtenus par délai ou avance de phase sont quantifiés non seulement par la phase du début de la sécrétion de mélatonine en lumière tamisée, mais également par le recoupement de l’épisode de sécrétion de mélatonine avec les périodes d’éveil et de sommeil. Les effets sur le sommeil et la vigilance d’un petit ajustement circadien partiel significatifs sont investigués dans une simulation de travail de nuit en laboratoire pour déterminer leurs implications cliniques. Les effets modestes suggèrent qu’un petit délai de phase peut réduire l’accumulation de la dette de sommeil, alors que l’avance de phase améliore subjectivement la vigilance et l’humeur nocturne. L’ampleur absolue du changement de phase est associée à une amélioration subjective de la vigilance et de l’humeur nocturne. Des études en milieux de travail permettraient de déterminer si ces stratégies sont applicables et bénéfiques aux travailleurs de nuit. / Night work is associated with many short and long term health problems. Misalignment between the circadian phase and the sleep-wake schedule causes a state of internal desynchrony considered as the main cause of these health problems. Circadian adjustment to night work is proposed as a countermeasure. Usually, complete circadian adjustment is not recommended because night workers experience circadian misalignment when returning on a day-active schedule, causing repeated circadian phase shifts and internal desynchrony. Therefore, partial circadian realignment was proposed as a compromise to stabilize circadian rhythms in night workers. However, the extent of partial circadian adjustment necessary to improve sleep and vigilance quality is still unclear. Here, partial adjustments obtained by phase delay or advance were quantified not only by the phase shift of dim light salivary melatonin onset, but also by the overlap of the melatonin production episode with the sleep-wake cycle during simulated night work. The effects of small but statistically significant partial circadian adjustments on sleep and vigilance quality were assessed in a laboratory simulation of night work to determine their clinical significance. Effects on daytime sleep and night-time vigilance quality were modest. They suggest that even small phase delays may decrease the accumulation of sleep debt, whereas the advance strategy improves subjective night work alertness and mood. Absolute phase shifts, by advance or delay, were associated with improved subjective night work alertness and mood. Field studies are needed, to determine whether these strategies can be adapted to real-life situations and provide effective support to night workers.

No description available.

No description available.

Regular use of illegal drugs is suspected to cause cognitive impairments. Two substances have received heightened attention: 3,4-methylenedioxymethamphetamine (MDMA or ‘ecstasy’) and δ-9-tetrahydrocannabinol (THC or ‘cannabis’). Preclinical evidence, as well as human studies examining regular ecstasy consumers, indicated that ecstasy use may have negative effects on learning, verbal memory and complex attentional functions. Cannabis has also been linked to symptoms of inattention and deficits in learning and memory. Most of the published studies in this field of research recruited participants by means of newspaper advertisements or by using word-of-mouth strategies. Because participants were usually aware that their drug use was critical to the research design, this awareness may have caused selection bias or created expectation effects. Focussing on attention and memory, this study aimed to assess cognitive functioning in a community-based representative sample that was derived from a large-scale epidemiological study. Available data concerning drug use history allowed sampling of subjects with varying degrees of lifetime drug experiences. Cognitive functioning was examined in 284 young participants, between 22 and 34 years. In general, their lifetime drug experience was moderate. Participants completed a neuropsychological test battery, including measures for verbal learning, memory and various attentional functions. Linear regression analysis was performed to investigate the relationship between cognitive functioning and lifetime experience of drug use. Ecstasy and cannabis use were significantly related to poorer episodic memory function in a dose-related manner. For attentional measures, decrements of small effect sizes were found. Error measures in tonic and phasic alertness tasks, selective attention task and vigilance showed small but significant effects, suggesting a stronger tendency to experience lapses of attention. No indication for differences in reaction time was found. The results are consistent with decrements of memory and attentional performance described in previous studies. These effects are relatively small; however, it must be kept in mind that this study focussed on assessing young adults with moderate drug use from a population-based study.

No description available.

Anyone desiring to qualify as an accountant or auditor is required to pass an examination as approved by the Public Accountants' and Auditors' Board to establish whether candidates have attained the required standard of academic knowledge in terms of the syllabi laid down by the Board, as well as whether they are able to apply that knowledge in practice (P AAB, 1995). However each year many students fail this very important examination. The reasons for this are not clear and the purpose of this research is to determine whether: personality; vocational interests; intelligence; matriculation Mathematics and home language (English/ Afrikaans) results, predict success in the QE, by comparing a group of successful and unsuccessful QE candidates. The logistic regression, discriminant analysis and t-test statistical procedures, indicated that: warmth (A), liveliness (F), rule-consciousness (G), social boldness (H), apprehension (0), self-reliance (Q2), perfectionism (Q3), tension (Q4), computational interest, social services interest, mechanical interest, Mental Alertness and matriculation home language, are significant factors to consider when identifying candidates likely to be successful in the QE. / Industrial & Organisational Psychology / MCOM (Industrial Psychology)

Nearly all functional magnetic resonance imaging (fMRI) studies are conducted in the supine body posture, which has been discussed as a potential confounder of such examinations. The literature suggests that cognitive functions, such as problem solving or perception, differ between supine and upright postures. However, the effect of posture on many cognitive functions is still unknown. Therefore, the aim of the present study was to investigate the effects of body posture (supine vs. sitting) on one of the most frequently used paradigms in the cognitive sciences: the N-back working memory paradigm. Twenty-two subjects were investigated in a randomized within-subject design. Subjects performed the N-back task on two consecutive days in either the supine or the upright posture. Subjective sleep quality and chronic stress were recorded as covariates. Furthermore, changes in mood dimensions and heart rate variability (HRV) were assessed during the experiment. Results indicate that the quality of sleep strongly affects reaction times when subjects performed a working memory task in a supine posture. These effects, however, could not be observed in the sitting position. The findings can be explained by HRV parameters that indicated differences in autonomic regulation in the upright vs. the supine posture. The finding is of particular relevance for fMRI group comparisons when group differences in sleep quality cannot be ruled out.

L'objectif de ce travail est de développer une méthode capable de déterminer automatiquement l'état de vigilance chez l'humain. Les applications envisageables sont multiples. Une telle méthode permettrait par exemple de détecter automatiquement toute modification de l'état de vigilance chez des personnes qui doivent rester dans un état de vigilance élevée (par exemple, les pilotes ou les personnels médicaux).Dans ce travail, les signaux électroencéphalographiques (EEG) de 58 sujets dans deux états de vigilance distincts (état de vigilance haut et bas) ont été recueillis à l'aide d'un casque à 58 électrodes posant ainsi un problème de classification binaire. Afin d'envisager une utilisation de ces travaux sur une application du monde réel, il est nécessaire de construire une méthode de prédiction qui ne nécessite qu'un faible nombre de capteurs (électrodes) afin de limiter le temps de pose du casque à électrodes ainsi que son coût. Au cours de ces travaux de thèse, plusieurs approches ont été développées. Une première approche propose d'utiliser un pré-traitement des signaux EEG basé sur l'utilisation d'une décomposition en ondelettes discrète des signaux EEG afin d'extraire les contributions de chaque fréquence dans le signal. Une régression linéaire est alors effectuée sur les contributions de certaines de ces fréquences et la pente de cette régression est conservée. Un algorithme génétique est utilisé afin d'optimiser le choix des fréquences sur lesquelles la régression est réalisée. De plus, cet algorithme génétique permet la sélection d'une unique électrode.Une seconde approche est basée sur l'utilisation du Common Spatial Pattern (CSP). Cette méthode permet de définir des combinaisons linéaires des variables initiales afin d'obtenir des signaux synthétiques utiles pour la tâche de classification. Dans ce travail, un algorithme génétique ainsi que des méthodes de recherche séquentielle ont été proposés afin de sélectionner un sous groupes d'électrodes à conserver lors du calcul du CSP.Enfin, un algorithme de CSP parcimonieux basé sur l'utilisation des travaux existant sur l'analyse en composantes principales parcimonieuse a été développé.Les résultats de chacune des approches sont détaillés et comparés. Ces travaux ont aboutit sur l'obtention d'un modèle permettant de prédire de manière rapide et fiable l'état de vigilance d'un nouvel individu. / The aim of this work is to develop a method able to automatically determine the alertness state of humans. Such a task is relevant to diverse domains, where a person is expected or required to be in a particular state. For instance, pilots, security personnel or medical personnel are expected to be in a highly alert state, and this method could help to confirm this or detect possible problems. In this work, electroencephalographic data (EEG) of 58 subjects in two distinct vigilance states (state of high and low alertness) were collected via a cap with $58$ electrodes. Thus, a binary classification problem is considered. In order to use of this work on a real-world applications, it is necessary to build a prediction method that requires only a small number of sensors (electrodes) in order to minimize the time needed by the cap installation and the cap cost. During this thesis, several approaches have been developed. A first approach involves use of a pre-processing method for EEG signals based on the use of a discrete wavelet decomposition in order to extract the energy of each frequency in the signal. Then, a linear regression is performed on the energies of some of these frequencies and the slope of this regression is retained. A genetic algorithm (GA) is used to optimize the selection of frequencies on which the regression is performed. Moreover, the GA is used to select a single electrode .A second approach is based on the use of the Common Spatial Pattern method (CSP). This method allows to define linear combinations of the original variables to obtain useful synthetic signals for the task classification. In this work, a GA and a sequential search method have been proposed to select a subset of electrode which are keep in the CSP calculation.Finally, a sparse CSP algorithm, based on the use of existing work in the sparse principal component analysis, was developed.The results of the different approaches are detailed and compared. This work allows us to obtaining a reliable model to obtain fast prediction of the alertness of a new individual.

Anyone desiring to qualify as an accountant or auditor is required to pass an examination as approved by the Public Accountants' and Auditors' Board to establish whether candidates have attained the required standard of academic knowledge in terms of the syllabi laid down by the Board, as well as whether they are able to apply that knowledge in practice (P AAB, 1995). However each year many students fail this very important examination. The reasons for this are not clear and the purpose of this research is to determine whether: personality; vocational interests; intelligence; matriculation Mathematics and home language (English/ Afrikaans) results, predict success in the QE, by comparing a group of successful and unsuccessful QE candidates. The logistic regression, discriminant analysis and t-test statistical procedures, indicated that: warmth (A), liveliness (F), rule-consciousness (G), social boldness (H), apprehension (0), self-reliance (Q2), perfectionism (Q3), tension (Q4), computational interest, social services interest, mechanical interest, Mental Alertness and matriculation home language, are significant factors to consider when identifying candidates likely to be successful in the QE. / Industrial and Organisational Psychology / MCOM (Industrial Psychology)