Research master thesis | Psychology (research) (MSc)
open access
Bullying victimization is a major public health concern, because victims often experience long-term negative mental health outcomes. Longitudinal brain structure research in children is needed to...Show moreBullying victimization is a major public health concern, because victims often experience long-term negative mental health outcomes. Longitudinal brain structure research in children is needed to understand the possible mechanisms underlying the relation between bullying victimization and negative mental health outcomes. Previous research has shown that the fusiform gyrus, amygdala and vmPFC are impaired in victims. Therefore, this thesis examined the relation between victimization and fusiform gyrus, amygdala and vmPFC volume over time. We hypothesized that victims of bullying, compared to children uninvolved in bullying, would have a larger fusiform gyrus volume and a steeper volume increase. Furthermore, we hypothesized that victims of bullying, compared to children uninvolved in bullying, would have a smaller amygdala and vmPFC volume and a steeper volume decrease. The sample consisted of 156 children (62% female), aged between 7 and 9 years old at baseline, from the Leiden Consortium on Individual Development. At the beginning of the study, the Revised Olweus Bully/Victim Questionnaire was administered to measure bullying victimization and high-resolution structural MRI scans were taken. This was done again two years later. Children were classified as victims if they had been bullied regularly in the past two months. We did not find an effect of victimization on fusiform gyrus, amygdala and vmPFC volume. Future research examining the influence of victimization on both structural and functional brain development is needed to provide further insights, which can help inform the design of interventions to reduce the negative consequences of bullying victimization. The current findings emphasize the importance of protective factors that make a victim’s brain development resilient against victimization. This indicates a need for interventions targeting the development of social-emotional skills or the increase of family support.Show less
Research master thesis | Psychology (research) (MSc)
open access
Human decision-making in the context of value-based learning considerably deviates from the premise to always maximise short-term reward. This sort of behavioural variability has been attributed to...Show moreHuman decision-making in the context of value-based learning considerably deviates from the premise to always maximise short-term reward. This sort of behavioural variability has been attributed to exploration during the choice process and has been linked to the locus coeruleusnoradrenaline (LC-NA) system. A recent computational account implementing a “noisy” reinforcement learning (RL) model provides evidence that computational imprecision during the learning process contributes to behavioural variability in decision-making as well. In the present study, the role of the LC-NA system in modulating learning imprecision has been investigated, using a multi-modal approach including the newly developed noisy RL model, a double-blind pharmacological manipulation, and EEG. The responses of thirty participants in a decision-making task were investigated during two experimental sessions in which either atomoxetine, a NA reuptake inhibitor, or placebo was administered, and the model fit of the noisy RL model was tested against the classical RL model without learning imprecision parameter. Contrary to our expectations, we did not find evidence for a modulatory role of the LC-NA system of learning imprecision. However, in line with our expectations, increased NA levels did not impact exploratory behaviour either. Crucially, the noisy RL model outperformed the classical RL model assuming exact learning and learning imprecision led to a significant number of non-maximising decisions contributing to behaviour variability. Moreover, the exploratory EEG analyses on potential underlying mechanisms of learning imprecision suggest learning noise to emerge broadly during feedback processing, rather than within a certain time window. The current study provides further evidence for the importance of computational imprecision during value-based learning.Show less
Research master thesis | Psychology (research) (MSc)
open access
Across clinical assessment tasks, a statistical model trained on the assessments of one person (a person’s model) has been shown to be more accurate than the person on which the model is based, the...Show moreAcross clinical assessment tasks, a statistical model trained on the assessments of one person (a person’s model) has been shown to be more accurate than the person on which the model is based, the Model-over-Person effect. Because the language that people use to express their state of mind is clinically meaningful, the objective of this study was to examine whether the Model-over-Person effect extends to language assessments as well as to identify conditions in which the effect occurs. The accuracy of the assessments of a person versus a person’s model was measured as their agreement with a reference standard (the mean assessment of multiple assessors) in two conditions: 1) the assessment of single words and 2) the assessment of texts. Artificial Intelligence based language assessments were employed to create the person’s model. No Model-over-Person effect occurred in the assessment of single words or all texts (N = 500 words/texts). A small Model-over-Person effect took place for all three assessors in the assessment of the longer texts (⩾ 50 words; dz = .39-.42; n = 23 texts). This effect be explained by the finding that a high amount of input data can make an assessment more prone to human error. Additionally, the relation between the accuracy and different assessment and language characteristics indicated that a person’s model could be more accurate in case of a low agreement among assessors and that the accuracy is not related to the confidence of the assessor in the assessment. The results show how computational language assessments can complement a person in accuracy and may support the use of computational language models as decision-support in clinical decision-making.Show less
Research master thesis | Psychology (research) (MSc)
open access
Individuals with a lower socioeconomic status (SES) are at an increased risk for developing depressive symptoms. However, it has not been investigated whether this link is homogenous, or whether...Show moreIndividuals with a lower socioeconomic status (SES) are at an increased risk for developing depressive symptoms. However, it has not been investigated whether this link is homogenous, or whether specific depressive symptoms relate to SES differentially. In this thesis, I explored (1) which individual symptoms of depression are related to subjective social status (as a proxy for SES); (2) how specific indicators of SES are related to specific symptoms of depression; and (3) how the addition of stressors impacts the relations between SES indicators and depressive symptoms. I used data previously gathered from 448 students aged ≥18 at institutions of higher education in the Netherlands, as a part of the WARN-D study. Variables were assessed through a questionnaire that was administered online. I estimated three regularised partial correlation networks to explore shared variances among nine symptoms of depression, five indicators of SES, and seven stressors. The network analyses revealed that (1) subjective social status (as a proxy for SES) was negatively associated with guilt/worthlessness, depressed mood, anhedonia, trouble concentrating, and feeling tired, meaning that participants with higher scores on subjective social status had, on average, lower scores on these symptoms; (2) educational level (as one of multiple indicators of SES) was negatively associated with appetite disturbances, and the ability to get by financially was negatively associated with depressed mood, guilt/worthlessness, and appetite disturbances; (3) these associations diminished considerably or disappeared altogether when controlling for the stressor variables. Overall, all SES-depression associations were small in magnitude. The results suggest that patterns of depressive symptoms might differ between high-SES and low-SES individuals. Future research should explore the mechanisms behind these differences to guide prevention and intervention. My findings are consistent with previous research showing that symptom composite scores obscure important differences between individuals.Show less
Research master thesis | Psychology (research) (MSc)
open access
This study investigated whether suggestion and placebo effects can induce mystical experiences using the God Helmet, a placebo brain stimulation device. Seventy-nine participants wore the placebo...Show moreThis study investigated whether suggestion and placebo effects can induce mystical experiences using the God Helmet, a placebo brain stimulation device. Seventy-nine participants wore the placebo God Helmet for 45 minutes in sensory deprivation and were interviewed about their experience. A qualitative analysis showed that, although participants reported unusual experiences, these were distinct from their previous mystical experiences. Additionally, a permutation analysis revealed that participants rated the intensity of the God Helmet experience lower on average than their previous mystical experiences, suggesting that the God Helmet experiences are less intense. Nevertheless, the experiences induced by the God Helmet were reported as stronger than normal daydreaming and shared similarities with hypnagogic (falling asleep) states. In addition, a regression showed that individuals with more previous mystical experiences had more unusual experiences with the God Helmet and a higher Mysticism scale score, highlighting the importance of considering individual differences for understanding sensitivity to mystical-type experiences. Furthermore, as the God Helmet shows potential for inducing hypnagogic states within a 45-minute session, it has potential applications in sleep research and provides new avenues for investigating altered states of consciousness. However, as the God Helmet does not induce authentic mystical experiences with long-term positive effects, it is not an effective tool for investigating mystical experiences or applying them for therapeutic purposes.Show less
Research master thesis | Psychology (research) (MSc)
open access
Autism Spectrum Disorder (ASD) is a highly heritable disorder that is more prevalent in males than females. Genetic mechanisms of the sexual differentiation could therefore contribute to the sex...Show moreAutism Spectrum Disorder (ASD) is a highly heritable disorder that is more prevalent in males than females. Genetic mechanisms of the sexual differentiation could therefore contribute to the sex differences in ASD. An unexplored pathway lies in the potential contribution of the direct effect of the X chromosome imbalance. Due to the X chromosome’s implications in brain structure, the imbalance in X chromosomes could contribute to recently discovered sex differences in brain structure variance. As males showed larger brain structure variance, they have generally larger brain structure deviations compared to females. If increasing brain structure deviations relate to increased ASD risk, this mechanism could explain why males show higher ASD prevalence compared to females. To assess an influence of the X chromosome imbalance on sex differences in brain structure variance, we assessed the sex difference in brain structure variance in brain regions with a high and low expression of the X chromosome. We then assessed whether larger brain structure deviations related to increased ASD symptoms. This was examined in a population of typically developing individuals aged 7 to 14. The X chromosome expression did not affect sex differences in brain structure variance. Therefore, our results did not support an effect of the X chromosome imbalance on sex differences in brain structure variance. Additionally, brain deviation showed no relationship with ASD symptoms. Our results do not support a contribution of sex differences in brain structure variance to sex differences in ASD. Our findings could suggest potential influences of other downstream effects of the chromosomal imbalance and the high heterogeneity of ASD.Show less
Research master thesis | Psychology (research) (MSc)
open access
Ecological momentary assessment (EMA) is a data collection method in which participants’ current behaviors and experiences are sampled repeatedly in their natural environment. EMA has advantages...Show moreEcological momentary assessment (EMA) is a data collection method in which participants’ current behaviors and experiences are sampled repeatedly in their natural environment. EMA has advantages over retrospective research methods, in that it reduces retrospective bias, increases ecological validity, and offers the possibility to observe dynamical changes of variables. However, EMA protocols are burdensome for participants and may interfere with their daily activities. This can lead to non-compliance over the course of a study. Missing data can subsequently decrease statistical power, and even induce bias. This paper explored whether missing data can be predicted by various variables related to students’ primary motivation to participate, mental health, stress levels, and demographics. We analyzed data of the first cohort (N = 418) of the ongoing WARN- D project on student mental health. Participants completed a comprehensive baseline survey and took part in an 85-day long EMA study. We predicted overall rates of non- compliance by participant characteristics at baseline (Analysis 1) and weekly rates of non- compliance by time-varying factors during the EMA stage (Analysis 2). Analysis 1 showed that overall non-compliance can be predicted by baseline measures such as age, depression, substance use, and primary motivation to participate. Analysis 2 showed that weekly assessed time-varying measures like time into study, enjoyment of the study, weekly stress, anxiety, and depression may predict weekly rates of non-compliance. Participant’s sex and smartphone operating system were not related to overall non-compliance. Summarizing, non-compliance rates of participants can be predicted by participant characteristics at baseline as well as by time-varying predictors. Our findings may inform future research on potential mechanisms behind noncompliance in EMA designs that should be considered to maximize participation rates while avoiding biased conclusions.Show less
Research master thesis | Psychology (research) (MSc)
open access
Ecological Momentary Assessment (EMA) is a data collection method that utilizes phone apps to gather data in daily life. EMA has many advantages, such as ecological validity. However, data...Show moreEcological Momentary Assessment (EMA) is a data collection method that utilizes phone apps to gather data in daily life. EMA has many advantages, such as ecological validity. However, data collection protocols are often intense, with multiple measurements per day, which can interrupt participants’ everyday activities and place a burden on them. This can reduce compliance. One way to tackle this is to provide participants with personalized data reports as an intrinsic reward. However, current frameworks to generate such reports are focused on single individuals in treatment, and not suitable for large-scale studies. Here we introduce a software to fill this gap, FRED (Feedback Reports on EMA Data), and showcase FRED by generating reports for 428 participants who took part in the WARN-D study. Participants were followed for 85 consecutive days, and received four daily and one weekly survey, resulting in up to 352 observations. We provided feedback to participants in the form of downloadable HTML-files, which were generated using the R programing environment. Reports included descriptive statistics, timeseries visualizations, and network analyses on selected variables. Furthermore, we assessed participants’ perceptions of the created reports (n=54), who judged reports mostly as understandable, insightful, and that reports resonated well with them. Given that FRED is flexible and can be adjusted to the needs of a particular research project, it provides a good basis to generate large numbers of personalized data reports.Show less
Research master thesis | Psychology (research) (MSc)
open access
Previous research has shown that subjective cognitive performance can be enhanced, and that sense of agency can be lowered via verbal suggestion of brain stimulation. Mixed results have been found...Show morePrevious research has shown that subjective cognitive performance can be enhanced, and that sense of agency can be lowered via verbal suggestion of brain stimulation. Mixed results have been found on the effect of placebo stimulation on error-related negativity (ERN) amplitude, which is an implicit outcome measure. This EEG study focused on the role of verbal suggestion and associative learning in eliciting placebo effects in subjective performance, sense of agency, and ERN amplitude. Using a within-subject design, we recorded EEG while participants (n = 19) performed in a simple cognitive task. Participants were told that a sham brain stimulation device would either enhance (placebo condition) or impair (nocebo condition) their cognitive performance. Next, we used a conditioning phase in which we altered the task difficulty according to the experimental block in order to induce the association between task difficulty and proposed stimulation. After this conditioning phase, the task difficulty was equal across conditions. We found increased subjective performance in the nocebo condition, but not the placebo condition, compared to control. We found a lower sense of agency in the placebo condition, but not the nocebo condition, compared to control. Finally, we found no difference in ERN amplitude throughout conditions. These results are not in line with previous research. Our conditioning phase did not work as intended and therefor the results are difficult to interpret. In addition, based on the results of our post-test questionnaire, our verbal suggestion might have been too weak. Future research should try to replicate the earlier results and continue investigating possible (other) implicit outcome measures.Show less
Research master thesis | Psychology (research) (MSc)
open access
The recent trend towards gamification could lead to an increase of the number of learning problems that need to be solved through reinforcement learning. It is therefore important that people learn...Show moreThe recent trend towards gamification could lead to an increase of the number of learning problems that need to be solved through reinforcement learning. It is therefore important that people learn how to solve reinforcement learning problems. Understanding which learning strategies people use, the processes behind them, and identifying sub-optimal learning strategies could prove very beneficial for teaching people the best reinforcement learning strategies. This study examines the processes behind reinforcement learning strategies through cognitive modeling. A reinforcement learning model was fitted on human behavior on a reinforcement learning problem. Some people were able to fully solve the problem and others were not. The temporal parameter trajectories of these two groups were compared to each other. The group that solved the problem showed expected results with a lot of learning and exploration at the start and less learning and more exploitation towards the end of the task. The other group started similarly but then started to learn less while exploration remained high. This could indicate that these people would benefit from short learning sessions after which they are able to focus on something else.Show less
Research master thesis | Psychology (research) (MSc)
open access
Identical sensory input may be perceived differently, based on expectations and goals. For example, object recognition is facilitated for expected or task-relevant objects. At the same time,...Show moreIdentical sensory input may be perceived differently, based on expectations and goals. For example, object recognition is facilitated for expected or task-relevant objects. At the same time, unexpected objects are found to elicit a stronger neural response. These effects can be explained by predictive coding accounts of visual processing, presenting perception as a process of minimizing the difference between predicted and observed sensory input. However, as expectation and task-relevance are often conflated, it is insufficiently clear how these factors influence sensory processing in conscious perception. The current study aimed to investigate the relative influence of expectation and task-relevance on behavioral and neural measures of perception. During two EEG sessions, participants performed a task in which they discriminated between masked face and house images while we independently manipulated expectation and task-relevance. We find that images were more often correctly recognized when they were expected or task-relevant. In addition, we used multivariate pattern analysis to show that a classifier trained on sensory representations of face and house stimuli is better able to distinguish between expected or task-relevant face and house images than between unexpected or task-irrelevant images. These results suggest that expectation and task-relevance have independent effects on sensory processing. Finally, our results show that cue-based manipulations may activate sensory templates even before stimulus onset. We therefore recommend that future studies manipulate expectation and task-relevance without the use of explicit cues.Show less
Research master thesis | Psychology (research) (MSc)
open access
Recent work has shown that we can achieve a better understanding of learning behavior by integrating reinforcement learning models with evidence accumulation models (RL-EAM). RL-EAM predict that as...Show moreRecent work has shown that we can achieve a better understanding of learning behavior by integrating reinforcement learning models with evidence accumulation models (RL-EAM). RL-EAM predict that as people learn they respond faster and more accurately. However, two recent experiments showed that when learning under speed pressure, people demonstrated a learning-related increase in accuracy, but not in response speed. We hypothesized that this might be caused by a proportion of responses resulting from a timing accumulation process that keeps track of time in parallel to the evidence accumulation process during a decision. We compared RL-EAM with and without the addition of time estimation on data from two independent experiments. We found no compelling evidence that the proposed mechanism of time estimation aid in decision-making in learning.Show less
Research master thesis | Psychology (research) (MSc)
open access
Evidence-based mental health programs have long conceptualized mental disorders as interactions between thoughts, feelings, behaviours and external factors. Idiographic network models are a...Show moreEvidence-based mental health programs have long conceptualized mental disorders as interactions between thoughts, feelings, behaviours and external factors. Idiographic network models are a relatively novel way of estimating such intra-individual psychological processes. These methods are not without limitations, and concerns have been raised about the stability and accuracy of estimated networks. The extend to which idiographic networks are stable, or vary over time, is unknown. We explored temporal network stability from three angles, exploring variation within people, across different stability metrics, and across people. We reanalysed daily symptom records of people with personality disorders. We fit graphical Vector Autoregressive models separately for the first and second 50 days of consecutive measurements. Contemporaneous but not temporal idiographic networks appeared to be relatively stable within people. The assessment of stability varied considerably across metrics applied. There was large variation in network stability of contemporaneous structures across people, which could not be explained by subject-specific variables. We illustrate the temporal changes in contemporaneous network structures of two participants with high and low network stability and discuss the most pressing questions to be considered by future research.Show less
Research master thesis | Psychology (research) (MSc)
open access
Eating disorders (EDs) are characterized by extreme symptom heterogeneity within diagnostic categories, which complicates treatment and inherently causes high relapse rates. The ability to predict...Show moreEating disorders (EDs) are characterized by extreme symptom heterogeneity within diagnostic categories, which complicates treatment and inherently causes high relapse rates. The ability to predict ED course in individuals would support clinicians in identifying early warning signals of relapse and to intervene accordingly. Traditional approaches have considered EDs as the shared origin of all symptoms which are reflective of a disorder, hindering prediction as it does not allow to unravel mechanisms of symptom progression. Network analysis provides new insights on EDs as it allows to model symptoms as networks of mutually causal relationships. However, most network analysis studies are limited as they only allow for conclusions on group-level at one single time point. By using time series data and intraindividual networks we can incorporate both individual and temporal information yielding insight in within-person variations over time. In this proof-of-concept study, we predicted ED severity using time series and intra-individual network features derived from ecological momentary assessment data in a transdiagnostic ED sample (n = 63). We explored whether time series and network features added to model performance on top of demographic and clinical features using machine learning and what features were most predictive of ED severity. Our findings show no convincing evidence that time series and network features improve predictive accuracy. Nonetheless, some time series and network features were identified as important, highlighting their potential clinical value. We consider our proposed combination of intra-individual networks and machine learning as a starting point towards personalized prediction of psychological outcomes.Show less
Research master thesis | Psychology (research) (MSc)
open access
Attention plays a vital role in helping the brain adaptively disambiguate between relevant and irrelevant information in the environment. Lapses in attention can thus have important negative...Show moreAttention plays a vital role in helping the brain adaptively disambiguate between relevant and irrelevant information in the environment. Lapses in attention can thus have important negative consequences, varying from small mishaps to life-threatening mistakes and as such it is important to study their mechanisms. Neural entrainment appears to play an important role in attention and researchers have long tried to explore the relationship between the two. Unfortunately, a majority of studies on the topic relies heavily on animal and clinical studies, often using invasive measurement techniques. What is more, some of the non-invasive methods used (such as eye-tracking), sometimes offer contradicting results and lack methodological consensus. The current work is part of a larger study looking at the relationship between attentional lapses and neural entrainment using a multimodal oddball task. Here, we focused solely on eye tracking and set out to investigate whether lapses in attention correspond to changes in tonic pupil size and whether measures of attentional lapses suffer from time-on-task effects. Participants performed an oddball dual-modality task in which they were presented with two simultaneous streams of stimuli (visual and auditory) and had to attend and respond to either visual or auditory targets. We found that the number of false alarms reduced significantly over time and that pupil size showed a decreasing (albeit not significant) trend, while the number of hits did not appear to decrease as time passed. These findings seem to be in partial consensus with previous research on the topic. We also found a significant difference in pupil size between the two attending modalities (attend visual and attend auditory), suggesting that visual and auditory stimuli may influence attention (or at the very least pupil diameter) differently. There was however no difference in any of the behavioral measures based on the attended modality. Similarly, no effect of the pupil size was found for our behavioral measurements, suggesting that An investigation of the relationship between attentional lapses and pupil size 4 pupil size does not necessarily predict behavior. It must be noted however that while our results appear to contradict previous findings from the literature, our sample size is likely too small to draw any generalizable conclusions fromShow less
Research master thesis | Psychology (research) (MSc)
open access
Death by suicide a global health problem, often preceded with the experience of suicidal ideation. Both depression and anxiety increase the risk of experiencing suicidal ideation. However, the...Show moreDeath by suicide a global health problem, often preceded with the experience of suicidal ideation. Both depression and anxiety increase the risk of experiencing suicidal ideation. However, the specific relations between symptoms of depression and anxiety on the one hand, and suicidal ideation on the other, remain unexplored. Therefore, we investigated these relations both at the cross-sectional (N = 2981) and the temporal level (N = 2596), with a follow-up time of 2 years. We included data from the NESDA study and controlled for the covariates age and gender. To do so, we used unregularized network models, each consisting of 21 nodes. In each network, 10 nodes represented depression items, 10 nodes represented anxiety items, and one node represented suicidal ideation. Results showed that the relation between suicidal ideation and depression was stronger than the relation between suicidal ideation and anxiety. This held true at the cross-sectional and temporal level. Overall, depression and anxiety symptoms at baseline explained about 15% of suicidal ideation at the cross-sectional level, and up to 13% at the temporal level. However, these percentages are not directly comparable, because only for the temporal analyses did we control for previous suicidal ideation. Results should be replicated and further investigated in order to be able to draw firm conclusions.Show less
