Early dementias are difficult to distinguish from normal age-related memory decline. In the preclinical stages of Alzheimer’s disease and Huntington’s disease, brain functions are already changing... Show moreEarly dementias are difficult to distinguish from normal age-related memory decline. In the preclinical stages of Alzheimer’s disease and Huntington’s disease, brain functions are already changing, but this is not directly visible from the outside. Many research is aimed at discovering early disease markers. However, research using EEG registration during conventional eyes closed conditions revealed little additional information. The yield of EEG research can be improved by probing the weakest spot, which, in case of dementia, is memory. Karin van der Hiele introduced memory tests during EEG registration and found that early abnormalities in brain functioning can then be observed in Alzheimer’s disease and Huntington’s disease. An interesting finding came to light: the EEG in dementia displays a lot of muscle activity which is normally filtered out. However, the researchers decided not to throw this activity away but to measure it. Interestingly, they found that the amount of muscle activity was related to cognition and to the number of depressive complaints. It may pay to keep an open mind regarding the nature of the parameter to be measured. Show less
This dissertation provides a balanced picture of the experiences that individuals can have in the combination of their work and family roles. Extending the common focus in previous literature on... Show moreThis dissertation provides a balanced picture of the experiences that individuals can have in the combination of their work and family roles. Extending the common focus in previous literature on experiences of role conflict (and their detrimental consequences), the present research also addresses the positive side of role combination and reveals the different ways in which work and family roles can facilitate each other (energy-based, time-based, behavioral, and psychological facilitation). This research shows that experiencing work-family facilitation has beneficial consequences for employees__ well-being at work and at home (e.g., higher work satisfaction, higher life satisfaction), contributes to employees__ mental and physical health (e.g., lower depressive complaints, lower cholesterol level, healthier body weight), and results in concrete gains for the organization as well (e.g., enhanced objective job performance, lower absenteeism). Furthermore, this research indicates that facilitation can be stimulated by means of informational (appraisal) support and by providing support for family issues in the work environment (a family supportive work environment) as well as support for work issues at home (a work supportive home environment). Thus, this dissertation provides a positive perspective on the combination of work and family roles, which hopefully also find its way to a non-academic audience. Show less
The studies in this thesis concentrate on memory for an emotional event, with a specific focus on completeness, consistency and accuracy of emotional memories and their predictors. In doing so,... Show moreThe studies in this thesis concentrate on memory for an emotional event, with a specific focus on completeness, consistency and accuracy of emotional memories and their predictors. In doing so, both field and laboratory studies were conducted. The results show that overall, memory for emotional events is fairly complete and consistent over time. Still, the human memory is sometimes incomplete and prone to inaccuracies and inconsistencies. Maybe an elephant never forgets, people occasionally do! Emotional state, psychiatric status and psychological variables, with the exception of (peri) traumatic dissociation, did not have a strong influence on completeness, consistency and accuracy of memory for emotional events. Show less
In the social and behavioral sciences, data sets often do not meet the assumptions of traditional analysis methods. Therefore, nonlinear alternatives to traditional methods have been developed.... Show moreIn the social and behavioral sciences, data sets often do not meet the assumptions of traditional analysis methods. Therefore, nonlinear alternatives to traditional methods have been developed. This thesis starts with a didactic discussion of nonlinear principal components analysis (NLPCA), illustrated by an application considering caregiver-child interactions in day-care. Traditional PCA explores data structures, summarizing the observed information in underlying variables, called principal components. The method only gives a sensible solution if the variables are numeric, and linearly related to each other. NLPCA is developed for situations in which these assumptions do not apply. It incorporates different types of variables (nominal, ordinal, and numeric) and discovers and handles nonlinear relationships. As PCA does not make assumptions about variable distributions, it does not seem theoretically sensible to apply standard (asymptotic) formulas for statistical inference. Therefore, this thesis shows easily applicable ways of assessing stability and statistical significance of the elements of the NLPCA solution (eigenvalues, component loadings, component scores, category quantifications) without making prior assumptions about the data (i.e., nonparametrically), using the bootstrap and permutation tests, respectively. By providing relatively simple inferential measures for NLPCA, a wider use of this method in the psychological and educational context may be promoted. Show less
This dissertation focuses on social dilemmas, and more specifically, on environmental uncertainty in these dilemmas. Real-life social dilemma situations are often characterized by uncertainty. For... Show moreThis dissertation focuses on social dilemmas, and more specifically, on environmental uncertainty in these dilemmas. Real-life social dilemma situations are often characterized by uncertainty. For example, fishermen mostly do not know the exact size of the fish population (i.e., resource size uncertainty). Several researchers have therefore asked themselves the question as to how such uncertainty influences people’s choice behavior. These researchers have repeatedly concluded that uncertainty is detrimental to the collective because it induces over-harvesting. The present dissertation aims to provide a more comprehensive view on uncertainty in social dilemmas. Whereas earlier research has primarily investigated how uncertainty influences harvesting decisions, this dissertation also focuses on how environmental uncertainty affects interpersonal processes. This dissertation introduces a perspective that argues that environmental uncertainty hampers the application of the equal division rule, which in turn influences how group members interact with one another. In six chapters, I elaborate on numerous implications of this notion. By focusing on three key aspects of interpersonal processes (i.e., tacit coordination, justification pressures and interpersonal emotions), and by testing my ideas in seven empirical studies, I demonstrate that the effects of uncertainty are much more differentiated than is portrayed in earlier research. Show less
The central topic of this thesis is the CATREG approach to nonlinear regression. This approach finds optimal quantifications for categorical variables and/or nonlinear transformations for numerical... Show moreThe central topic of this thesis is the CATREG approach to nonlinear regression. This approach finds optimal quantifications for categorical variables and/or nonlinear transformations for numerical variables in regression analysis. (CATREG is implemented in SPSS Categories by the author of the thesis; the relevant parts of the Categories manual are included in the appendix.) The first chapter of the thesis provides a non-technical introduction to the CATREG approach, illustrated with graphs. The more technical part of the thesis includes (1) a solution to the local minima problem for monotone transformations, as well as a study of the effect of several data conditions on the incidence and severeness of local minima, (2) the incorporation into CATREG of a particular resampling method (the .632 bootstrap) for assessing prediction accuracy, and (3) the incorporation into CATREG of several regularization methods (Ridge Regression, the Lasso, and the Elastic Net) for stabilizing the estimates of the regression coefficients and transformations. The technical part is followed by a chapter describing a bulimia nervosa study in which the CATREG-Lasso and the .632 bootstrap are applied. Show less
This thesis investigates the mechanisms of stimulus-driven visual attention (global saliency), the mechanisms of top-down visual attention, and the interaction between these mechanisms, in visual... Show moreThis thesis investigates the mechanisms of stimulus-driven visual attention (global saliency), the mechanisms of top-down visual attention, and the interaction between these mechanisms, in visual search. Following the outline of an existing model of top-down visual attention, namely the Closed-Loop Attention Model (CLAM), simulations in this thesis explore mechanisms of visual working memory in the prefrontal cortex and of object recognition in the ventral pathway, and specify mechanisms of spatial selection in the dorsal pathway. Behavioral experiments additionally address several questions regarding stimulus-driven and top-down visual attention in visual search, and their interaction. The findings of the simulations and behavioral experiments have implications for CLAM in particular, and for the mechanisms of global saliency and top-down visual attention in general. Show less
How do social peer interactions (i.e. verbal helping behavior) during a cooperative learning (CL) curriculum in math affect the mathematical, linguistic, and social skills of 10-12 year old pupils... Show moreHow do social peer interactions (i.e. verbal helping behavior) during a cooperative learning (CL) curriculum in math affect the mathematical, linguistic, and social skills of 10-12 year old pupils from multiethnic classrooms? We developed a CL math curriculum in this thesis to investigate this question, consisting of: (a) a CL training (two lessons), (b) a CL math curriculum (nine lessons), and (c) an individual math exam. During the CL math curriculum, pupils were either stimulated to use verbal helping behavior in their peer interactions (experimental condition), or not stimulated (control condition). Being in the experimental condition proved beneficial for national pupils__ math scores, pupils__ linguistic proficiency -especially that of immigrant pupils - and pupils__ verbal helping behavior. Irrespective of condition, immigrant pupils displayed less helping behavior than national pupils. Mathematically high-achieving immigrant pupils were more motivated to cooperate in the control condition than in the experimental condition. Furthermore, the CL experience increased team members__ cooperativeness and popularity, and decreased the difference in cooperativeness and popularity between immigrant and national team members. Popularity and cooperativeness only increased within ethnically heterogeneous teams, extending the notion that enduring interethnic contact is fruitful for interethnic friendships. The implications of these results are discussed. Show less
The central issue in this thesis is the work related causes and consequences of job stress among nurses. The relationships between a wide range of work characteristics and characteristics of the... Show moreThe central issue in this thesis is the work related causes and consequences of job stress among nurses. The relationships between a wide range of work characteristics and characteristics of the organization and environment on the one hand, and different outcomes (such as job satisfaction and emotional exhaustion) on the other hand are explored in three studies. The influence of goal orientation on the outcomes is studied in a fourth study. Data were gathered by means of questionnaires that were spread among all nurses of the Leiden University Medical Centre in 2000 and in 2003. Nurses’ job satisfaction is influenced by their possibilities to develop nursing skills and by having good working relationships with supervisors. Nurses’ ill health is largely determined by their workload. However, it seems not (necessarily) to be the emotional demand of patient contact that burdens nurses. More likely, ill-health is the effect of the fact that nurses cannot give each patient the attention they want to give, due to too many tasks. The thesis deals with methodological issues such as causality. Moreover, it deals with theoretical issues such as the influence of person and environmental factors on the stress reaction. Finally, practical considerations are outlined. Show less
The present thesis deal with the diagnostic boundaries between hypochondriasis and obsessive compulsive disorder and between hypochondriasis and another somatoform disorder called non-cardiac chest... Show moreThe present thesis deal with the diagnostic boundaries between hypochondriasis and obsessive compulsive disorder and between hypochondriasis and another somatoform disorder called non-cardiac chest pain. These studies showed that hypochondriasis and both other disorders are valid disorders based on diagnosis-specific symptoms. Furthermore, in the thesis the first randomized controlled trial comparing the efficacy of cognitive behavioural therapy, and a double-blind SSRI (paroxetine) and pill-placebo is described. The short term effects (4 months) and the long term (5 years) of both treatments were compared to each other and to the placebo. It can be concluded that both are effective treatments for hypochondriasis compared to the placebo in the short term, but the significant differences between both active treatments in ameliorating hypochondriacal symptoms disappears during the follow-up, although CBT is more effective in ameliorating comorbid depressive and psychoneurotic symptoms during the follow-up period than the placebo. Furthermore, CBT results in less use of additional psychological or medical help during the follow-up. Finally, the psychometric properties of the first clinician-administered semi-structured interview, the hypochondriasis Y-BOCS, were described. This interview seemed reliable and valid addition to the assessment arsenal measuring hypochondriacal symptoms. Show less
The artificial grammar learning experiments reported in this thesis pertain to the question of whether implicit learning is ineluctable and unselective or selective and accidental. The results of... Show moreThe artificial grammar learning experiments reported in this thesis pertain to the question of whether implicit learning is ineluctable and unselective or selective and accidental. The results of Chapter 2 showed that implicit learning was negatively affected by complexity, suggesting that the process does not automatically acquire any structure present in the environment. Chapter 3 provided direct evidence that implicit learning is selective. When two aspects of the structure could facilitate the participants__ task in the induction phase, only the most useful aspect was selected and learned implicitly. Chapter 4 showed that explicit learning could be more successful than implicit learning when participants were specifically instructed to look for rules of letter-order. In Chapter 5, implicit learning was demonstrated when the structure was useful to the participants__ induction task, but not when it was useless. This finding was replicated in 10 to 11-year-old children in Chapter 6. Chapter 7 showed that the negative effect of complexity could not be counterbalanced by adding a semantic reference field. These findings indicate that implicit learning is a selective process that does not occur ineluctably. Rather than being accidental, however, implicit learning seems to occur whenever the structure is useful to one__s current task. Show less
The objective of the research described in this thesis was to study single and cumulative family risk in relation to early childhood externalizing problems and the effectiveness of a parenting... Show moreThe objective of the research described in this thesis was to study single and cumulative family risk in relation to early childhood externalizing problems and the effectiveness of a parenting intervention program. The Video-feedback Intervention to promote Positive Parenting and Sensitive Discipline (VIPP-SD) aimed at reducing externalizing problems in 1- to 3-year-old children by enhancing parental sensitivity and adequate discipline strategies. An evaluation of the process of this intervention was also conducted. The study consisted of a screening phase in a general population sample (N = 2408) and a randomized case-control intervention phase in a selected sub-sample of children with high levels of externalizing behaviors (n = 237). The results of this thesis showed that even at an early age, family risk predicted child externalizing behaviors. Cumulative risk longitudinally predicted externalizing behaviors, but was not related to the effectiveness of the intervention. Further, first-time parents (primiparas) profited differently from the intervention than parents with more than one child (multiparas). Finally, a positive alliance between mother and intervener predicted change in positive parenting strategies. Show less
Being a member of a socially devalued group (e.g., women, ethnic minorities) threatens social identity, leading people to lower their investment in performance domains that determine societal... Show moreBeing a member of a socially devalued group (e.g., women, ethnic minorities) threatens social identity, leading people to lower their investment in performance domains that determine societal status (e.g., education, career success). The experiments discussed in this dissertation show that offering devalued group members information that affirms their social identity improves their motivation in status-defining domains. Firstly, it was shown that contexts that express value for positive characteristics of devalued groups motivate group members towards higher achievement on status-defining dimensions. Secondly, this motivational effect of social identity affirmation held up even in threatening intergroup contexts in which high status outgroup members were present. When outgroup members acknowledged positive characteristics of the devalued group, devalued group members became focused on approaching success rather than avoiding failure. Thirdly, the beneficial effects of social identity affirmation compared to self-affirmation were revealed: Whereas self-affirmation led devalued group members to be concerned with their individual outcomes, affirming group identity challenged group members to pursue collective action. The findings underline the importance of positive group identity and intergroup respect for status-improvement of low status groups. Implications of the results for the integration of ethnic minorities and the participation of women in the work force are discussed. Show less
The aim of this thesis was twofold: Firstly to create a reliable and valid new instrument to measure maladaptive social behaviour (MSB) of students in secondary vocational education, and secondly... Show moreThe aim of this thesis was twofold: Firstly to create a reliable and valid new instrument to measure maladaptive social behaviour (MSB) of students in secondary vocational education, and secondly to assess which school context variables could predict MSB at school. Three data-waves were conducted between December 2001 and July 2003. At the first data-wave 1800, at the second 931, and at the third 642 students participated from several schools, several departments, and several courses, spread over the Netherlands. Using several pilot-studies a new instrument was developed: The Questionnaire for Maladaptive Social Behaviour (QMSB). It consists of 49 items referring to five categories of behaviour: MSB toward Schoolwork and Rules, Delinquent Behaviour, Unfriendly Behaviour, Withdrawn Behaviour and Impolite Behaviour. Three studies were conducted to explore external validity of the instrument. Boys reported more MSB for all categories than girls. When controlled for gender, no differences in MSB were found between students with different ethnic origin, course level, or educational level of parents. School context variables predicted a small amount of variance of MSB. For Boys, feeling alienated from school appeared the most important predictor for their MSB at school; it predicted each type of MSB. For girls, the perception of a competitive school environment predicted their MSB best. Show less
