From company board committees to grand juries to political parties, decision making often involves a group of individuals with differing views on what the best decision may be. Individuals have different views, in part, because some individuals have more knowledge than others. In theory, decision makers can make better decisions by leveraging the expertise of individuals in the crowd by identifying those who have more knowledge than others. Unfortunately, it is often difficult to identify and leverage expertise in practice. Decision makers often have no records of individuals' past performance from which they can estimate expertise, and subjective measures such as confidence and self-ratings of expertise are often considered as unreliable. In this thesis, I demonstrate how individuals' meta-predictions -- predictions about what other individuals will predict -- can be used to identify and leverage expertise in the crowd on 'single-question' problems, where records on individuals' past performance are unavailable. I first examine how a recent algorithm in the literature can be used to distinguish between subsets of high-performing and low-performing individuals in the crowd on binary decision problems. I show that this algorithm is in fact weighting individuals by the absolute difference between an individual's vote and their meta-prediction about the votes of others, and thus this weighting metric can be used to identify and leverage expertise in the crowd. I develop an improved weighting approach that uses individuals' probabilistic forecasts and their meta-predictions about the average probability forecast of others, and show that this outperforms the top alternative probabilistic aggregation approaches in the literature on a large range of decision problems. Furthermore, I demonstrate that this improved weighting approach provides a superior measure of expertise than existing single-question approaches to identifying expertise in the literature. As an additional test, I compare this single-question approach with cross-domain weighting -- weighting by individuals' performance on problems on unrelated domains -- and show that cross-domain weighting is favoured over single-question approaches in cases where it is possible to obtain individuals' past performance on problems -- even if those questions are from unrelated domains. In general, our results demonstrate the potential for using individuals' meta-predictions and performance on problems from unrelated domains to identify expertise in cases where other approaches might be ineffective or unavailable.

Diagnosing Alzheimer’s disease (AD) in its earliest phases is difficult. A combination of standardised cognitive testing with AD-related biomarkers such as medial temporal atrophy observed on neuroimaging scans has been proposed to improve the diagnostic process of AD detection. The availability of automated volumetric segmentation software presents as a promising avenue for the incorporation of quantitative volumetric measures into routine clinical workup. However, the performance of these automated protocols in a clinical context remains to be clarified. This thesis aimed to examine the use of automated segmentation in a “real-world” clinical setting against the gold standard of manual segmentation, assess the difficulties surrounding reliable automated measurements, and evaluate the relationship between volume, diagnosis, and memory function. Methods utilised to address the research questions included a review of the diagnostic accuracy of various diagnostic tools, in-depth examination of structural variations that could undermine automated segmentation efforts, a series of validation studies, and assessment of medial temporal volumes and memory function in samples of clinical and healthy controls. The results indicate that a multimodal approach to diagnosis that includes a combination of cognitive assessment and other biomarkers would likely yield a more accurate diagnosis. Although automated segmentation of the medial temporal structures was promising for the hippocampus, the entorhinal and transentorhinal cortices were inherently more challenging to delineate and produced much poorer reliability measures. Medial temporal structural volumes contributed little beyond what was already provided by comprehensive memory assessment for distinguishing between the clinical and healthy control samples. Taken altogether, these findings highlight the need for additional refinement of automated algorithms and further investigation into the ideal combination of cognitive testing and other biomarkers.

This thesis was on organizational neuroscience with applications to stress management. Section 1 developed an organizational neuroscience model of occupational stress that integrated the health impairment process of the job-demands resources model of occupational stress with the (biologically-grounded) allostatic load model of stress. In doing so, this section developed a series of propositions that integrated each model through a job demands-allostatic load pathway. Resilience training was discussed as a potential moderator of this pathway with a focus on mindfulness meditation, physical activity, and multi-modal interventions that comprise each of these practices completed concurrently. In Section 2 of this thesis, specific methodological, interpretational, and philosophical concerns that arise when adopting an organizational neuroscience approach to research were discussed across two critical essays. This included a focus on the appropriateness of statistical analyses in organizational neuroscience, the implications of the completeness and transparency of reporting research findings, and what kind of causal inferences can be drawn about organizationally-relevant behavior using neuroscience data. These essays served as the statistical and philosophical framework through which the empirical studies conducted in Section 3 were conducted and interpreted. Finally, Section 3 of this thesis was a conceptual evaluation of the resilience training propositions of the theoretical model developed in Section 1. It was a conceptual evaluation in that the sample was one of convenience rather than a working population, specifically. This included three studies conducted within a pilot and feasibility trial that comprised formal mindfulness psychoeducation and aerobic endurance exercise training, completed concurrently. It has been theorized that interventions of this kind exert salutary effects on mental health outcomes through neurobiological mechanisms. To assess this, this intervention was evaluated at multiple levels of analysis to build a comprehensive understanding of its effect on the mind, brain, and physiology. The primary aim of Study I was to investigate the effect of this intervention on self-reported chronic psychosocial stress, and potential mechanisms involving dispositional mindfulness, adaptive and maladaptive emotion regulation strategies, and maximal and submaximal cardiorespiratory fitness. Notably, participation in this intervention was associated with a reduction in chronic psychosocial stress, and an improvement in wellbeing that is considered clinically meaningful with respect to the scale. The primary aim of Study II was to investigate whether the effects of this intervention on mental health outcomes may occur through neural mechanisms, as predicted by theoretical models. This involved a longitudinal voxel-based morphometry study with a focus on gray matter concentration within the hippocampus. This study provided preliminary evidence that this intervention was associated with increases in gray matter concentration within the hippocampus, as well as within regions associated with stress regulation, memory, and sensorimotor processes. The primary aim of Study III was to investigate whether the aerobic endurance training component of this intervention was associated with exercise-induced adaptations to stress-responsive systems. This is of note because these adaptations have been posited to spill over to heterotypic stressors like psychosocial stress, and confer resilience to adversity more broadly. This was evaluated through measuring the cortisol response to a submaximal steady state exercise bout before and after the training period. In this study it was identified that training was associated with an attenuation of cortisol responses, which was indicative of physiological adaptations that enable submaximal exercise workloads to be conducted with greater efficiency and less strain. Limitations and implications for future research were also discussed.

This thesis examined the way in which information is combined in order to make decisions. It focused specifically on within-dimension decision-making with spatially separate stimuli. The primary aim was to characterize the underlying organization of processing over time (i.e., identify the processing architecture; whether information processing proceeds in serial, parallel, or is pooled into a single decision-making channel), stopping rules (i.e., whether the process is exhaustive or self-terminating), and the efficiency of processing (i.e., workload capacity). These attributes were assessed through the analysis of response times (RTs) using Systems Factorial Technology (SFT), the Logical-Rules paradigm, and relevant computational modeling. In the first part of the thesis, results from the categorization experiments showed that for the majority of participants, processing occurs coactively (i.e., is pooled into a single decision process). Workload capacity, however, was shown to be limited. This suggests that a violation of context invariance may have occurred and several theories are considered as potential explanations for this finding. In the second part of the thesis, a novel modeling framework for characterizing the time course of change detection based on information held in visual short term memory was presented. Specifically, we sought to answer whether change detection is better captured by a first-order integration model, in which information is pooled from each location, or a second-order integration model, in which each location is processed independently. We conducted two experiments with both disjunctive OR rules and conjunctive AND rules (across locations) using a double factorial paradigm and a redundant target paradigm. These experiments showed that although capacity is generally limited in both tasks, architecture varies from parallel self-terminating in the OR task to serial self-terminating in the AND task. This novel framework allowed for model comparisons across a large set of models, ruling out several competing explanations of change detection. As a whole, this thesis found both differences and similarities in decision-making using within-dimension stimuli across categorization and change detection tasks. The finding of differences in decision-making strategy across categorization and change detection tasks highlights that different perceptual operations can yield a variety of experimental results. It may be expected that other tasks such as visual search, identification, and detection might also diverge. A finding of limited capacity across both task types, however, points to a potential common bottle neck in processing efficiency at an earlier encoding stage.

Functional Neurological Disorder (FND) is a condition that encompasses a wide spectrum of neurological symptoms that do not have an organic explanation. It is not clear why some patients develop a specific neurological symptom. In our study we considered the most frequent FND sub-types: functional motor disorders (FMD) and non-epileptic seizures (NES). It has been purported that individuals with risk factors, create strong expectations about body sensations based on clinical experiences such as disease, injury or surgery. These expectations would impact the nervous system which in turn lead to functional symptoms. These symptoms are inconsistent in frequency and evolution across time, and they are vulnerable to suggestion. Thus, there are no objective measures that can account for the symptoms. This thesis aims to determine whether previous clinical factors affecting different parts of the body have a relationship with the development of functional motor disorder (FMD) and non-epileptic seizures (NES), and to carry out a preliminary study of a measure capable of identifying perceptual differences in patients with functional weakness, the most reported symptom. In the first study we analysed the medical records of 108 FND patients (52 FMD and 56 NES), and in the second study we applied the Size-Weight Illusion (SWI) to 11 FND patients with functional weakness and 15 healthy controls (HC). It was found that patients with motor symptoms (FMD) had significantly higher rates of clinical factors that affected their limbs prior to the symptom onset than NES. Moreover, contrary to predicted, patients with NES had a similar rate of events that affected their head than FMD. However, NES had a higher rate of clinical factors during their lifetime than FMD, such as dissociative symptoms, suicidal ideation, and being victim of bullying, which affect the mind, and from the patients’ perspective they can be considered as located in the head. In the second study, FND and HC experienced a similar size-weight illusion. The severity and laterality of the symptom did not impact on the strength of the illusion, nor the dominance of the affected side. However, we propose that it is likely to find an effect in FND with a larger sample size. Otherwise, if similar results were found in future studies, the SWI might be a test that provides an objective assessment to confirm FND has a normal perception of weight relative to size.

It has been recently claimed that measures of spontaneous electroencephalography (EEG) signal complexity, such as Lempel-Ziv Complexity (LZc), can provide an index of an individual’s level of consciousness. Research and clinical practice are currently limited to unreliable behavioural and physiological measures to indicate consciousness. Therefore, there is significant urgency for an objective, reliable, brain-based measure of consciousness. EEG complexity measures utilise algorithms from Information Theory to quantify the diversity in spontaneous EEG data. These are being used to measure the diverse neural activity which necessarily underlies conscious experience. LZc assesses the complexity of multi-channel EEG data using a compression algorithm. Studies of LZc typically involve comparing conditions of altered consciousness with periods of conscious wakefulness. These studies suggest that the change in complexity observed is reflective of the change in level of consciousness. However, very little is known about how LZc varies, either with or without a corresponding change in consciousness. The present study utilised portable long-wear EEG to record multi-day, continuous EEG data from two participants (a total of 8 days for Participant 1 and 4 days for Participant 2). Data from each participant was analysed independently. A LZc algorithm was used to compute a complexity value for every non-overlapping 10-second segment. Results demonstrated that, as with previous research, LZc during Wake (14-hours during the day, multiple days per participant) is, on average, higher than during sleep (Stage N1, Stage N2, Slow-Wave-Sleep, and REM sleep). However, there is considerable variation surrounding these means. Visualising LZc across Wake revealed a consistent but wide spread of variability around the mean, with a scattering of low LZc values reflected by a negative skew in the data. This also results in a wide range of possible mean LZc values made available from taking samples (between 1 and 120 minutes in duration) during this period. Although this variability reduces with larger samples sizes, even day-to-day, LZc can significantly differ within a person. Regardless of the source of this variability, its presence causes concern due to the overarching clinical motivations and potential practical applications of this measure. These results suggest that LZc may not be indicative of level of consciousness, as previously claimed. The issues raised and addressed in this study are not unique to LZc, but will apply to all complexity algorithms, current and future. With this study, we have shown that long-duration EEG is a successful framework for identifying variability in a complexity measure of consciousness. This information-rich dataset is uniquely capable of exposing and investigating complexity measures, with the additional insight of observing and analysing complexity across time. This study endeavours to redirect discussions of this field and promote the use of this framework to both acknowledge and empirically address all surrounding issues and assumptions. All complexity measures should undergo reliability testing as both a proof of concept and a proof of practice before being utilised in research or clinical applications.

During the key periods of adolescence and emerging adulthood, individuals can be particularly vulnerable to experiencing suboptimal wellbeing and functioning. With potential long-term impacts on adult trajectories, early wellbeing promotion is critical. This study aimed to further understand wellbeing development across adolescence and into emerging adulthood, by examining the role of a range of individual and environmental characteristics. The individual characteristics examined included temperament, anxiety symptoms, and depression symptoms. Environmental characteristics included parental responses to emotion expression, parental mental health, stressful life events, and maltreatment. The role of emotion regulation strategies were also explored in relation to the characteristics and wellbeing. The study utilised a longitudinal community cohort from the Adolescent Development Study, recruited from schools across Melbourne, Australia. The sample included 245 families who completed questionnaires across three time points. At time 1 (mean age = 12.45), measures of temperament, depression symptoms, anxiety symptoms, parental depression symptoms, parental anxiety symptoms, and parental responses to offspring emotion expression were completed. At time 2 (mean age = 15.01), adolescents completed measures of stressful life events and maltreatment. They completed emotion regulation and wellbeing measures at the final time point (mean age = 18.83). Predictor variables were factor analysed within each domain in order to provide sufficient representation of the structure of the data. A series of path analyses, controlling for gender and SES revealed that temperament traits, neglect, and abuse predicted wellbeing and functioning outcomes. Bootstrap path analyses (using 95% confidence intervals for the indirect effect) revealed significant associations between the emotion regulation strategies of rumination, distraction, mindfulness, cognitive reappraisal, and expressive suppression with the individual and environmental characteristics, and wellbeing and functioning outcomes. Findings suggest that wellbeing development across adolescence and emerging adulthood is associated with individual characteristics (e.g., temperament), as well as environmental experiences that deviate from adaptive ranges (e.g., neglect). The various patterns found in the study reinforce the salience of examining wellbeing as a multifaceted construct, with aspects of wellbeing potentially having different developmental pathways. Furthermore, emotion regulation strategies may be important for wellbeing pathways, with maladaptive strategies (e.g., rumination) being associated with lower wellbeing and adaptive strategies (e.g. mindfulness) associated with higher wellbeing. Therefore, emotion regulation may be a suitable target for optimising youth wellbeing.

Autism Spectrum Disorder (ASD) is a complex neurodevelopmental condition characterised by impairments in two core domains of social communication deficits and restricted, repetitive behaviours or interests. A milder variant of autism-like characteristics, known as the Broader Autism Phenotype (BAP), is present at higher rates in relatives of individuals with ASD than the general population, indicating a genetic liability for ASD. There is a wealth of social cognitive research documenting theory of mind, empathising, and emotional face processing deficits in ASD and the BAP, which correspond to abnormal brain function in the “social brain”. However, less research has been conducted on the brain and behavioural correlates of emotional voice processing in ASD and the BAP, despite its significance for social cognition. This thesis aimed to profile emotional voice processing abilities in ASD and the BAP in relatives and the general population, specifically relating to non-linguistic vocalisations known as vocal affect bursts (e.g., laughter, cries, screams). This thesis also aimed to identify the neurobiological substrates of emotional voice processing in individuals with ASD and relatives with the BAP. Three studies were performed to address these aims, each using the same purpose-built, web-based and/or functional MRI (fMRI) task to assess behavioural performance and elicit brain activation. Whole-brain activation elicited by the fMRI task was assessed using random- and fixed-effects analyses (RFX and FFX), which allowed inferences to be made on the population and sample levels, respectively. Study 1 examined vocal affect burst recognition and its neurobiological correlates in individuals with high-functioning ASD (n = 16) compared to typically-developing controls (n = 16). The ASD group demonstrated a vocal emotion recognition deficit on the web-based task, where they misclassified neutral non-linguistic voices as expressing basic emotions at a higher rate than controls. RFX analyses revealed no significant group differences in brain activation, whereas FFX analyses revealed that the ASD group demonstrated higher activation relative to controls in widely distributed regions associated with emotional voice processing, executive function, memory, motor and somatosensory processing, and visual processing. These findings enable atypical brain activation to be inferred for this specific ASD cohort, but not for the wider ASD population. Although cohort-specific, such information may facilitate hypothesis generation for future investigations of neurobiological compensation in ASD. Study 2 addressed the same research questions as Study 1 in relatives of individuals with ASD (n = 13) who were determined to have the BAP on clinical assessment. The BAP group demonstrated no vocal emotion recognition deficit relative to controls (n = 13) on the web-based task. Under FFX analyses alone (not RFX analyses), the BAP group demonstrated significantly higher activation in the left lateral occipital cortex relative to controls. Inferences about the FFX findings are limited to the specific BAP cohort assessed here, and cannot be extended to the wider population of ASD-relatives with the BAP. Nonetheless, these findings may inform new hypotheses exploring endophenotypes (i.e., intermediate phenotypes) of ASD, characterised by a similar expression of neurobiological compensation in ASD and the BAP. Study 3 used the web-based task to assess the association between vocal affect burst recognition and the continuous distribution of BAP traits in the general population of individuals without a family history of ASD. It was hypothesised that lower recognition accuracy for the six basic emotions would correlate with higher self-ratings of BAP traits. In contrast to expectations, higher classification accuracy (and emotional intensity ratings) for angry voices correlated significantly with higher self-ratings of rigid BAP traits. The specific anger-rigid association indicates that enhanced auditory threat detection constitutes an aspect of the BAP in the general population. Further research is recommended to examine whether this relationship is mediated by underlying personality factors like neuroticism or trait anxiety. Overall, different behavioural profiles of emotional voice processing abilities were observed in individuals with ASD (deficit—misclassifying neutral voices as being emotional), relatives with the BAP (no deficit—intact performance), and individuals from the general population with higher levels of BAP traits (advantage—enhanced sensitivity to angry voices). The neuroimaging findings of enhanced activation in the specific ASD and BAP cohorts assessed here may have implications for future research investigating the role of neurobiological compensation for emotional voice processing in their respective populations, potentially including the exploration of endophenotypes of ASD. Such studies would ideally include larger ASD and BAP (relatives) samples that enable the assessment of more homogenous, identifiable subgroups who may be susceptible to increased cognitive demands for emotional voice processing. This thesis extends research on social cognition within the voice modality in ASD and the BAP, and may have wider implications for understanding the genetic aetiology of social communication impairments in ASD.

Many theories of number propose that humans possess a ‘mental number line’ (MNL) representation. The MNL is commonly measured with a number-to-position (NP) task, and this task is often used to make inferences about the MNL representation. However, most research on MNL representations to date has made assumptions about the properties of the MNL without considering the role of ordinal relationships between numbers. The research reported in this thesis examined whether the MNL metaphor should be extended to include ordinal relationships, and to examine the nature of these relationships. A pilot study tested whether a linear MNL representation could be shifted with logarithmic training. Adults completed a series of logarithmic feedback sessions, and their NP task performance was assessed at the end of each training block. Findings revealed little to no systematic effect of logarithmic training on NP task performance, despite participants successfully learning the logarithmic function. They also revealed individual differences in the overall impact and learning of the logarithmic feedback. These findings suggested that relationships between numbers may change to allow accurate task performance, which may not be reflected in the NP task. Study 1 tested whether the linear response profile that describes NP performance is specific to number, or whether this pattern of responding is a feature of ordered lists more generally. Adults were given NP and alphabet-to-position tasks. Findings showed that numbers and letters both displayed similar linear trends. This suggested that the linear profiles attributed to number may reflect the way in which ordinal lists of symbols are learned. Studies 2a and 2b investigated whether leaning a list of novel symbols is mediated by the underlying spatial properties of the symbols (e.g., spatial complexity). Novel symbols were used to minimise the overlearned nature of Hindu-Arabic numerals. Study 2a aimed to determine the ideal novel symbol set to use in Study 2b, specifically, one which could be ordered by complexity. Participants made judgements on two novel symbol sets, and their relationship to a range of numerical stimuli. In Study 2b, a paired comparisons training method was used to teach participants the order of a list of novel symbols. Participants were allocated to either a spatial complexity or a random complexity condition, and made judgements regarding which of two symbols was numerically ‘larger’. When novel symbols were ordered by spatial complexity, learning was facilitated. These findings showed that the spatial complexity and relational information of symbols may mediate the construction of ordered representations. This suggests that a common cognitive representation underlies all ordinal lists. Overall, the findings of this research indicate that a more nuanced account of the MNL representation is required, particularly in terms of ordinal relationships between numbers. The findings also suggest that the NP task measures ordinal lists more generally. Arguably, the way in which ordered lists are learned, combined with the relative relationships between symbols, may account for performance on the NP task, and the MNL metaphor should be extended to account for these ordinal relationships.

Intimate partner violence (IPV) is a widespread problem. Worldwide, 1-in-3 women have experienced some form of violence in their lifetime, and the majority of incidents are the result of male perpetrated IPV. Scholars suggest that objectification facilitates IPV, because the phenomenon involves perceiving and/or treating a person as an object or not as fully human. Despite these theoretical claims, objectification has not been studied extensively in the realm of heterosexual romantic relationships – the most common setting for women to experience violence. The purpose of this thesis was to explore how objectification among heterosexual men relates to the perpetration of physical, sexual, and psychological IPV within romantic relationships. I divided the study of objectification into two distinct, but complementary approaches – examining the phenomenon from implicit (Study 1 and 2) and explicit (Study 3) standpoints. Two correlational studies investigated objectification implicitly by measuring the extent to which men associated women and romantic partners with objects and/or animals. A third behavioural experiment investigated objectification explicitly by measuring the extent to which manipulating the phenomenon facilitated male physical aggression towards the romantic partner, and impacted on judgments about the objectified target’s humanness, mind, and moral status (referred to as personhood). Study 1 examined how automatically likening women to non-human entities (animals, objects) played a role in IPV perpetration in romantic relationships. Findings demonstrated that men who held implicitly objectifying perceptions of women were more likely to perpetrate sexual and physical IPV against their current female partner. Study 2 builds on the finding that men who objectify women are more prone to commit IPV, and examined whether the finding would replicate when assessing the objectification of an intimate partner. This study also examined the relation between partner-objectification and physical aggression, particularly in the context of provocation. Results showed that men’s tendency to implicitly perceive their romantic partner as an object predicted self-reported perpetration of physical IPV. They also revealed that objectification moderated the effect of provocation on physical aggression, whereby highly provoked men enacted more physical IPV against their female partner when they held stronger associations of that woman with objects and/or animals. Study 3 then experimentally investigated the effect of explicit partner-objectification, induced via an appearance-focus mindset, on denials of personhood to the target. This study also extended the novel correlational finding that objectification predicted physical IPV, and examined a causal link between partner-objectification and physical aggression towards the romantic partner, in the context of provocation. Results demonstrated that when the romantic partner was objectified by a focus on her physical appearance, she was stripped of her personhood and perceived as lacking humanity and mind. They also demonstrated a direct aggression-facilitating effect of partner-objectification, and of provocation, wherein these variables increased physical IPV. Together, the findings from these three studies indicate that objectification has profoundly negative manifestations and consequences for women in romantic relationships. Not only did the phenomena relate to greater male perpetrated sexual and physical IPV within romantic relationships, but men’s partner-objectification also diminished perceptions of the romantic partner as possessing full personhood, and directly and indirectly facilitated enacted physical aggression against the same partner. This thesis thus provides compelling evidence that objectification—implicit or explicit—is a likely contributor to the victimisation of women in romantic relationships. As such, our research can help inform prevention and intervention efforts to reduce this major social problem.

Many contemporary proposals of bilingualism conjecture that domain-general Executive Functions (EFs) are fundamental to language control. These proposals revolve around two main observations: the first is that bilinguals have been shown to demonstrate superior performance on tasks used to measure non-linguistic EFs, and the second is that language switching superficially appears to relate to switching between tasks (a process which has been associated with EFs) in that they both induce a Response Time (RT) cost. Critically, direct evidence for the involvement of EFs in both non-linguistic and linguistic bilingual processing have not been demonstrated, but merely speculated. In this thesis, I present a series of four analyses, where I explicitly investigate the presence of EFs in bilingual processing by expressing their impact as a set of cognitive model parameter changes to task performance. The results reveal that bilingual behaviour across both the non-linguistic and linguistic domains do not exhibit signs of EFs, but instead demonstrate the influence of other lower-level general cognitive processes. The main conclusions of this thesis are as follows: A) the putative bilingual advantage is attributed to enhanced selective attention and B) language switches are attributed to automatic bindings between language information and response. These findings are discussed in terms of their implications for current frameworks of language control and bilingualism in general.

Personality traits are the main currency of the field of personality psychology. However, historically there has been much confusion concerning the conceptualization of traits in relation to context, which remains unclear to date. Some personality psychologists have proposed that traits are internal and decontextualized dispositions that account for consistency in behaviour and experience across time and situations, whereas others have argued that traits are patterns of behaviour and experience that are contextualized and require appropriate eliciting stimuli for manifestation. Although there is a long history of research on the interplay of traits and situations, the contextualized view has received little attention and not yet been systematically examined in empirical studies. This thesis aims to evaluate the contextualized view of traits, and to clarify what is meant exactly when describing someone as high or low on a personality trait, specifically in relation to context. When we call someone an ‘extravert’, are we describing their typical patterns of behaviour and experience across all contexts, or are we describing their typical patterns of behaviour and experience in particular contexts? Among all traits, extraversion and neuroticism are perhaps the best understood in terms of eliciting stimuli—reward and threat, respectively— which have been described and incorporated in several personality theories. For this reason, they are the focus of this thesis. It is expected that traits will predict their corresponding expressions most strongly within situations containing relevant eliciting stimuli. The hypotheses were: (a) the relation between trait extraversion and patterns of state extraversion would be the strongest within contexts characterized by rewarding stimuli; and (b) the relation between trait neuroticism and patterns of state neuroticism would be the strongest within contexts characterized by threatening stimuli. A collection of four studies were designed to examine the contextualized nature of extraversion and neuroticism using different methodologies. The first study was an online survey, examining the hypotheses by asking participants to imagine their behaviour in certain context, the second one in a controlled lab environment, and the third and the fourth studies in people’s everyday life context using experience sampling methods. Across these studies, a mixture of subjective and objective measures of personality states and situations were employed. All four studies showed that extraversion and neuroticism significantly predicted state extraversion and state neuroticism, respectively, across all contexts. Meanwhile, state extraversion was significantly higher in rewarding contexts and state neuroticism was significantly higher in threatening contexts—both within-person and between-persons. However, the magnitude of the relation between trait and state extraversion, or between trait and state neuroticism, did not vary strongly across contexts. Although the results differed slightly depending on the study, the trait (extraversion vs. neuroticism), and the measure used (subjective vs. objective situation ratings), overall there was very weak evidence that trait-state associations vary across context. These findings therefore suggest trait extraversion and neuroticism are not strongly contextualized. These findings have broad theoretical implications for understanding what a trait is in relation to context. Additionally, some findings may have theoretical implications for how traits influence experiences of situations via situation perception and selection processes. Some practical implications concern the use of situation reappraisal as a coping strategy to improve people’s functioning in different contexts. Future studies could extend this thesis by examining the contextualized view in relation to other trait domains, aspects, and facets. They could also explore personality’s effects on situations more rigorously to disentangle the various mechanisms concerned with situation perception, situation selection, situation transformation, and situation evocation. Furthermore, they could apply these understanding to improve people’s wellbeing and facilitate personality change.