It is unclear whether the depression experienced by individuals with recent onset schizophrenia spectrum disorders (termed SSD hereafter) is similar or different to the depression experienced in recent onset major depressive disorder (MDD), and whether it is best conceptualised as distinct from or intrinsic to SSD, particularly in the psychotic phase. A better understanding of depression will aid in improving early recognition and treatment of depression to improve outcomes in SSD. The overarching aim of the current research program was to gain a better understanding of the extent and phenomenology of depression in SSD. Only then can appropriately tailored treatments for depression be recommended in SSD. The current research program comprised four studies, the primary aims of which were to determine: (1) the extent of depression — based on different operationalisations — across the psychotic and post-psychotic phases in SSD; (2) how depression should be assessed in SSD; (3) the specific phenotype of depression in SSD and how it compares to MDD; (4) and whether depression is best conceptualised as a distinct or intrinsic feature of SSD in the psychotic phase. Methods included systematic review and meta-analysis (Study 1), and network analyses of cohort or trial data (Studies 2 – 4). The systematic review was conducted in accordance with an a priori protocol, registered with the International Prospective Register of Systematic Reviews (PROSPERO; CRD42018084856), and conforming with the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) and Meta-Analysis of Observational Studies in Epidemiology (MOOSE) guidelines. Studies 2 – 4 involved individuals with recent onset SSD (drawn from the Psychosis Recent Onset GRoningen Survey [PROGR-S]) or recent-onset MDD (unipolar, without psychotic features; drawn from the Youth Depression Alleviation [YoDA] trials). Measures included the Montgomery–Asberg Depression Rating Scale (MADRS) and Positive and Negative Syndrome Scale (PANSS). Key findings were: (1) that depression is highly common in SSD, and is even more common and severe in the psychotic compared to post-psychotic phase (Study 1); (2) that depression can be assessed with the Montgomery–Asberg Depression Rating Scale (MADRS) — a depression scale designed for use in MDD but not SDD — but that specific tailoring is needed to ensure its validity in SSD (Study 2); (3) that the specific phenotype of depression might be different in SSD compared to MDD; while sadness is the hallmark of depression in both SSD and MDD, individuals with SSD are more likely to present with atypical neurovegetative features including increased sleep (Study 3); and (4) that depressive symptoms are highly interrelated with positive symptoms, and negative symptoms pertaining to deficits in motivation and interest, in the psychotic phase of SSD (Study 4). Rather than being conceptualised, assessed, and treated as a comorbidity akin to MDD, depression might be better conceptualised as intrinsic to SSD, with assessment and treatment needing to be tailored accordingly. Limitations included the use of assessment models developed in MDD to gain a better understanding of depression in SSD, and the cross-sectional design. Future mixed methods research is needed to gain a more in-depth and phenomenologically valid understanding of depression in SSD and, in turn, develop a new scale for its recognition and assessment. Then, using this new scale, research is needed to model the trajectory and psychophysiological mechanisms of depression in SSD. This would improve early and accurate recognition of depression in SSD and reveal when and how to treat it, and ultimately contribute to better outcomes for individuals with SSD.

Cosmetic surgery is extremely popular. Despite this, negative attitudes towards cosmetic surgery and its recipients prevail. This thesis contains five manuscripts that examine pervasive perceptions of cosmetic surgery in contemporary society. The first manuscript contained within this thesis empirically demonstrates that cosmetic surgery recipients face stigmatisation; namely, that recipients are assumed to be less warm, competent, moral, and human than non-recipients. The second manuscript is a narrative review that examines the cosmetic surgery paradox – a contemporary phenomenon whereby women are conflictingly both compelled to undergo cosmetic surgery and condemned for doing so. Specifically, this manuscript describes how unattainable beauty standards for women are responsible for popularising cosmetic surgery on a societal level while contributing to the individualistic stigmatisation of its recipients. Manuscript three further explains why cosmetic surgery recipients may face stigmatisation. By examining cosmetic surgery stigma through a moral lens, this manuscript suggests that preferences for ‘naturalness’ might drive the societal condemnation of cosmetic surgery (i.e., cosmetic surgery is wrong because it is unnatural). Manuscript four depicts cosmetic surgery recipients’ anecdotal lived experiences of stigmatisation. Findings from this manuscript suggest that women who undergo cosmetic surgery are aware of the stigmatisation they face, internalise this stigmatisation, and actively employ strategies to navigate and manage this stigma on a day-to-day basis. Finally, manuscript five examines whether intrasexual competitiveness compels women to derogate and socially exclude cosmetic surgery recipients. Contrary to our predictions, manuscript five demonstrates that intrasexual competitiveness does not motivate cosmetic surgery stigma. Overall, findings from these five manuscripts considerably broaden our understanding of cosmetic surgery stigma. In particular, this thesis suggests that cosmetic surgery recipients are stigmatised because of pervasive societal preferences for natural beauty and that recipients ongoingly manage experiences of stigmatisation. Taken together, findings provide building blocks upon which interventions for eradicating cosmetic surgery stigma may be built.

Many personality psychologists argue that the Big Five (Goldberg, 1990) provides an organising framework for psychological traits. However, in the wider psychology literature, the Big Five is frequently not adopted as an organising framework for stand-alone psychological trait scales. In the current thesis, I aimed to: evaluate whether the Big Five could accommodate these stand-alone scales; examine whether scale users could navigate the Big Five effectively; and consider impediments to the wider adoption of the Big Five (or a comparable taxonomy, e.g., the HEXACO; Lee & Ashton, 2004). In Chapter 2, I developed a method to assess how well the Big Five could accommodate stand-alone scales. In Chapter 3, I applied this method in three convenience samples, followed by a community sample in Chapter 4. In Chapter 5, I evaluated the accuracy of psychological researchers predictions of associations between stand-alone scales and the Big Five domains to determine how well they could navigate the Big Five. In the General Discussion, I explored further challenges to the Big Five's wider adoption. In Chapter 2, various shortcomings with using Exploratory Factor Analysis and Extension Analysis for the present task were identified, before an Exploratory Structural Equation Modelling (Asparouhov & Muthen, 2009) approach was selected. Applying this method in Chapter 3, the Big Five accommodated over 70% of stand-alone scales, such that many of the scales assessed might reasonably be considered Big Five facets. Many stand-alone scales demonstrated incremental validity beyond the Big Five domains, but so did Big Five facets. This can be understood in terms of the bandwidth-fidelity trade-off. In Chapter 4, nearly half the stand-alone scales could be readily located within the Big Five. The result was less compelling than that of Chapter 3, but was likely attributable to methodological factors that diminished or obscured associations between the Big Five and stand-alone scales in the sample. In Chapter 5, psychological researchers were reasonably accurate regarding the locations of stand-alone scales within the Big Five. Based on these findings, I concluded that the Big Five would be an appropriate organising framework for stand-alone psychological trait scales, both in principle and in practice, and ought to be widely adopted as such. However, many researchers may remain indifferent to the Big Five if they perceive it to be of little benefit to their field, or hostile if they believe adopting the Big Five would undermine their fields' research programs. To counteract these objections, I argued that the wide adoption of the Big Five as an organising framework for stand-alone scales may accelerate scientific progress via reduced fragmentation or better measurement of existing constructs. I also suggested an integrative pluralism approach—whereby stand-alone scales with incremental validity beyond the Big Five continue to be used, but their relationships to the Big Five are acknowledged and incorporated into discussions of research outcomes. I finished by considering the scope of scales that ought to be included and the challenge posed by alternative frameworks.

A vast number of studies in different domains (e.g., workplace, educational, sports, among others) have demonstrated that moral disengagement is one the strongest predictors of unethical behaviour. By and large, moral disengagement comprises a suite of social cognitive mechanisms that operates by disconnecting people from their ethical standards so they can justify acting unethically and therefore avoid self-sanctions. Research has adopted a multilevel approach in the exploration of the antecedents of moral disengagement. For instance, a recent review of moral disengagement at the workplace proposed a distribution of several antecedents at three different levels of analysis: organizational, team/group, and individual. Within the individual level of analysis, research has explored, among many other factors, the role of Big Five personality domains on moral disengagement. Briefly, that research has highlighted the associations between domains agreeableness, conscientiousness (both negative), neuroticism (positive), and moral disengagement. Nonetheless, most of these studies have lacked designs that include a more comprehensive account of variables (e.g., confounders). In addition, that research do not take into account more complex models of Big Five personality factors that comprise, for instance, within-domains aspects that, if included, would help to better characterize the specific contribution of different features of each domain to moral disengagement. Additionally, research on moral disengagement and unethical behaviour has been mainly conducted in settings in which people are motivated by self-serving goals. One common goal people pursue in such contexts is higher status which, in turn, is based on social comparison processes. Hence, it is reasonable to think that to the extent people morally disengage to behave unethically in the pursuit of increasing their perceived status, social comparison processes would play a key role. Nevertheless, research on social comparison processes as antecedents of moral disengagement and unethical behaviour is scarce. One approach to explore this is the study of social comparison emotions as potential antecedents of moral disengagement. Furthermore, we centre on two social comparison emotions that are commonly found in competitive settings in which antisocial conduct has been usually found: envy and pride. Lastly, we focus mainly on trait envy and pride as we interested in exploring how the tendency to experience these emotions can lead people to engage in unethical behaviours. To achieve this aim we conducted a literature review and to first have a complete view of extant research on emotions and moral disengagement. Briefly, we found that studies exploring affective phenomena and moral disengagement have focused on general affective states, anger, and guilt, hence neglecting other relevant emotions like envy and pride. Among that research, studies notably failed to include other relevant control emotions to clearly establish the unique contribution of their target emotions. Lastly, even though most of these studies were contextualized in group settings (e.g., workplace, school), none of them explored group-level emotions. Therefore, in this thesis we addressed these gaps of both Big Five personality and emotion research in the context of moral disengagement. To achieve this, we developed three projects along two different streams. The first stream comprised one project addressed the exploration of Big Five domains and aspects as potential antecedents of moral disengagement and unethical decision-making across three correlational studies (Chapter 3). Additionally, we tested moral disengagement as a mediator candidate of the effects of Big Five factors on unethical decision-making and subsequently ran four meta-analyses on our data to better understand the effects found for each domain and aspects. In sum, these studies highlighted the main negative role of agreeableness and its aspect politeness, over compassion. Additionally, smaller effects were found for openness/intellect and its aspect openness (negative), extraversion (positive overall effect) and its aspects enthusiasm (negative) and assertiveness (positive), and neuroticism and its aspect volatility (positive). Lastly, mediation analyses showed that moral disengagement significantly accounted for the effects of these domains and aspects (except for domains neuroticism and extraversion) on unethical decision-making. The second stream of this thesis (chapters 5 to 10) comprised three projects and addressed the study of the associations between social comparison emotions, moral disengagement, and unethical decision-making. The first project of this stream (Chapter 5) explored, across two correlational studies, individual trait envy (based on upward social comparisons) by using a dual conceptualization of this emotion that differentiates between malicious, and benign envy. Findings from these studies confirmed the primarily significant, unique positive role of trait malicious envy (and the smaller positive effect for trait benign envy) on moral disengagement and unethical decision-making. Both trait malicious and benign envy’s positive effects on unethical decision-making were accounted for by moral disengagement. The second project of this stream (Chapter 7) centred on intergroup envy. Across two experimental studies we tested if individual and intergroup envy are differently related to moral disengagement and if intergroup malicious envy causes moral disengagement. Although Study 1 found initial evidence of a unique effect for intergroup malicious envy on moral disengagement for participants in a group-benefiting condition, Study 2 did not find causal effects for intergroup malicious envy on moral disengagement. Finally, in the third project of this stream (chapters 9 and 10) we moved from the upward social comparison emotion of envy to the downward social comparison emotion of pride. Concretely, in this project we first examined correlations between trait pride, moral disengagement, and unethical decision-making to then switch to state pride and experimentally tested its potential causal effect on moral disengagement. We focused on a dual conceptualization of pride rooted in comparison processes (i.e., social comparison-based, and self-comparison-based pride) but also included an influential model of pride based on controllable versus uncontrollable internal attributions (i.e., “authentic” pride, and “hubristic” pride). Findings of these studies showed the main positive association of trait social comparison-based pride to moral disengagement and unethical decision-making beyond other pride facets, trait emotions, and individual differences, as well as the role of moral disengagement in accounting for the effects of both social comparison-based and self-comparison-based pride on unethical decision-making. In sum, the studies compiled in this thesis contribute to current research on the antecedents of moral disengagement as they entail the first (separate) systematic account of both Big Five personality factors, and the social comparison emotions of envy and pride as potential antecedents of moral disengagement. Additionally, across this thesis, we presented moral disengagement as a consistent factor that may help to unveil the mechanisms by which both Big Five factors, envy, and pride may impact unethical decision-making. Finally, another central contribution of these projects is the comprehensive and strategic control of both individual differences and emotions to clearly reveal the unique effects of our target variables.

Our rich and complex visual world provides us with more information than our visual system can handle at any given time. To navigate in this world, we need to constantly search for relevant information, learn to identify objects, and be selective in the information that we memorise. In a series of papers, I investigate how people interact with their visual environment, in particular, how they search, learn, and remember the things that they see. The first paper explores the boundaries of attribute amnesia, a counter-intuitive phenomenon where people often "forget" an aspect of an object despite having attended to it mere seconds ago. Results showed that while people had difficulty recalling a colour or a repeated animal, they could accurately recall the identity of a novel animal. This suggests that attribute amnesia may only occur for repeated, familiar stimuli, hence explaining why we do not often observe it in the real world. The second paper addresses the low prevalence effect in real world visual search tasks where target rarity can lead to disproportionately high miss error rates. This is especially problematic in medical image interpretation as certain targets, such as cancerous lesions, can be very rare. In an attempt to lower miss errors while avoiding an increase in false positive identifications, a novel protocol was developed for mammogram screening. Unfortunately, miss errors were only reduced through a shift in response bias, and no improvement was observed in participants' ability to distinguish target from noise. As a result, the false alarm rate escalated substantially, hence we cannot recommend this protocol be trialled in a clinical setting. The final paper examines whether perceptual training should supplement the education program for radiology students that currently relies heavily on conceptual training, and how it can be optimized. It is demonstrated that novices improved rapidly in a hip fracture identification task and the more able students achieved the same level of accuracy as expert radiologist in less than an hour of training. Surprisingly, training novices on an image set that over-represented the more difficult images was detrimental to learning outcome. But repeating training images was as effective as showing an equivalent number of unique images. Consequently, perceptual training should be implemented in the current education programme as an effective way of teaching novices.

Background: The community of microorganisms inhabiting the gastrointestinal tract, collectively known as the gut microbiota, is intimately involved in the maintenance of host health. Comprehensive characterisation of the gut microbiota may enable us to better understand conditions whose pathophysiologies remain poorly understood, including internalising mental health disorders (anxiety and depressive disorders) and irritable bowel syndrome (IBS). While existing research has sought to characterise the gut microbiota in these conditions, the two systematic reviews included within this thesis reveal that studies have failed to consider essential confounders, including age, dietary intake, medication use, biological sex, and body mass index. The inadequate consideration of IBS and internalising disorder co-occurrence was also highlighted. Accordingly, this thesis aimed to investigate the gut microbiota in medication-free females with either IBS or an internalising disorder, as well as females with comorbid IBS and anxiety/depression, whilst controlling for key covariates (age, dietary intake, body mass index). Study 1 aimed to compare the gut microbiota of females with IBS relative to controls, as well as compare microbial composition between the three major IBS subtypes (IBS-diarrhoea, IBS-constipation, IBS-mixed). Study 2 aimed to characterise the gut microbiota of females with an internalising mental health disorder relative to controls. Study 3 aimed to compare and contrast the gut microbiota of females with comorbid IBS and an internalising disorder to controls, as well as to participants with IBS or an internalising disorder separately. Method: This thesis includes 162 females, recruited as part of the Bugs and Brains Study, who belonged to one of four groups: i) 42 controls; ii) 36 participants with an internalising disorder (depressive/anxiety disorder), but no IBS; iii) 42 participants with IBS, but no internalising disorder and iv) 42 participants with both an internalising disorder and IBS. Participants completed comprehensive questionnaires, attended a clinical mental health interview, collected a stool sample, and had their anthropometrics measured within a 1-month period. The gut microbiota was estimated using 16S rRNA gene sequencing on an Illumina MiSeq platform (V4 hypervariable region). Sequences were pre-processed using QIIME2 and following the DADA2 denoising pipeline to produce amplicon sequence variants (ASVs). ASVs were taxonomically assigned against the SILVA database (v.138). Data analysis was performed using R (v.1.3.1073), with the packages phyloseq and picante (alpha diversity), vegan (beta diversity), ANCOM-BC and MaAsLin2 (differential abundance), and randomForest (random forests). Results: Comprehensive multivariate analyses revealed key similarities with regards to the gut microbiota in IBS and anxiety/depression relative to controls. Females with IBS or an internalising disorder tended to be enriched in bacterial species associated with inflammation (e.g., Proteobacteria, Parabacteroides, Alistipes), and participants with either condition harboured a lower relative abundance of immunoregulatory SCFA-producing bacteria relative to controls (e.g., Barnesiella, Bacteroides eggerthii, Lachnospira, Faecalibacterium). Moreover, both the anxiety/depression and IBS groups had higher relative abundances of species known to degrade the essential amino acid tryptophan (i.e., Alistipes). While similar findings were observed in participants with comorbid anxiety/depression and IBS, the gut microbiota composition in this group was heterogeneous, and alterations were not more pronounced than those observed in participants with either disorder separately. Of note, higher abundances of mucin-degrading bacterial taxa were observed in IBS-C and IBS-M relative to controls and the IBS-D group (e.g., Akkermansia muciniphila), suggesting this alteration may be a unique to constipation. Conclusion: This thesis presents a comprehensive characterisation of the gut microbiota in females with IBS, an internalising mental health disorder, and their comorbidity. Similar alterations in the gut microbiota composition relative to controls were identified in these conditions and were not driven by their comorbidity, as participants in the IBS group had no lifetime history of a mental health disorder, and participants in the anxiety/depression group had no lifetime history of IBS. The included studies have great strength in highlighting these findings independent of key confounding factors, including age, dietary intake, BMI, and host sex. Participants in this study were also medication-free and without relevant medical comorbidities. While these studies are well placed to examine the cross-sectional associations between gut bacteria with IBS and internalising disorders, future research should seek to integrate functional analyses and examine other microbial members of the gut microbiota. Longitudinal research designs that combine taxonomic and functional investigations will elucidate the true complexity of gut microbe interactions with host mental health and gastrointestinal functioning.

Moral judgements play an important role in society - they shape interpersonal relationships, group dynamics, and form the basis for our legal and political systems. Yet, moral judgements are not made in isolation, but in a complex informational context. Further, moral judgements often need to be updated as we learn new information. However, the moral judgement process in such dynamic environments, and individual differences in moral judgement across informational contexts, are poorly understood. In this thesis a new paradigm was developed for studying moral judgements of fairness-related actions, which was used across three studies to derive novel insights into these issues. In Study 1 we characterised moral judgement updating, showing that people flexibly switch between relying on context-independent to relying on context-dependent moral norms, as they learn contextual information. While doing so, participants remained stable with respect to broader moral virtues of generosity, balance and (condemning) selfishness. In Study 2, we showed that individual differences in importance people assign to norms when making their decisions differed according to their personality, for both context-independent and context-dependent norms. The importance people placed on selfishness- and generosity-based norms in their judgements correlated with Agreeableness, Extraversion, Conscientiousness and Openness to Experience, stably across two judgements with and without contextual information. In Study 3, we showed that people slow their moral judgements when expecting contextual updates and when judging negatively valenced actions. Using the Diffusion Decision Modelling (DDM) framework, we show that these slowing effects can be understood as changes in distinct aspects of the unfolding decision process – shifts in the boundary settings (for context expectancy) and shifts in the bias parameter and the drift rate parameter (for valence). Across these studies, the thesis presents a new understanding of moral judgement as a highly context-sensitive and dynamic decision process, and suggests that this context-sensitivity may be supported by decision-making processes related to caution (and confidence). Moreover, I discuss the potential usefulness of DDM framework to aid further investigations of moral judgement processes and inform our understanding of neural underpinnings of moral judgements in information-dynamic settings.

Climate change is one of the biggest challenges our planet faces, and understanding human behaviour is key to changing its course. This research aimed to combine the strengths of two approaches to predict carbon-relevant household infrastructure behaviour: a top-down, reasoned action approach, and a bottom-up, social practice theory perspective. Four studies were conducted. Study 1 elicited beliefs about six carbon-relevant household infrastructure behaviours from both theoretical perspectives. It demonstrated that the two perspectives were indeed commensurable at the belief level, with each perspective eliciting different, complementary sets of beliefs underlying behaviour. Study 2 demonstrated that both of these sets of beliefs predicted behavioural intentions. However, of the contextual beliefs elicited by the social practice perspective, it was one type in particular that appeared to influence intentions – beliefs about the more concrete components of behavioural context. Studies 3 and 4 piloted and refined a practical behaviour change intervention, informed by the processes people appeared to follow in order to account for concrete contextual beliefs. This intervention influenced both intentions (indirectly) and hypothetical behaviour (directly). It was concluded that social practice and reasoned action approach perspectives are indeed commensurable, with each demonstrating unique value for predicting carbon-relevant household infrastructure behaviour, without compromising either. It was also concluded that the current standard social psychological, top-down behaviour paradigms currently dominating research and policy stand to benefit from a stronger focus on concrete behavioural context, such as that provided by a social practice theory perspective.

Personality psychology investigates individual differences in emotion, behaviour, cognition, and motivation, whereas cognitive neuroscience investigates the neurobiological bases of these phenomena. This substantial content overlap suggests that these areas are well placed to integrate knowledge. Accordingly, I present results from two empirical research programs that demonstrate how combining theories and methods from personality psychology and cognitive neuroscience can provide a new perspective on outstanding research questions and spur novel research programs. Part 1 (Studies 1-5) assessed how theory from personality psychology can address a current question in cognitive neuroscience: why people seek information that provides no extrinsic reward. One explanation is that uncertainty is aversive, and information reduces this uncertainty. This would suggest that the personality trait uncertainty intolerance would relate to information seeking. However, this conflicts with a theory from personality psychology whereby openness/intellect (describing tendencies toward imagination and intellect; thought to relate to greater tolerance for uncertainty) is grounded in increased information seeking. Because no explicit confirmatory study has assessed the putative negative relation between uncertainty intolerance and openness/intellect, Study 1 (N = 308) investigated—and confirmed—these relations. Next, Studies 2 (N = 151) and 3 (N = 301) assessed personality trait correlates of information seeking to gauge relative evidence for either conflicting theory. Openness/intellect did not predict information seeking; however, joyous exploration (a facet of curiosity positively related to openness/intellect) predicted information seeking across both studies, and uncertainty intolerance predicted information seeking in Study 3. These results informed a conceptual model featuring two motivations to seek information—either to explore (related to joyous exploration and openness/intellect) or to feel safe (related to uncertainty intolerance and neuroticism)—each differentially elicited depending on how the situation is perceived. To evaluate this model, Study 4 (N = 436) assessed personality and situation perception predictors of information seeking across four stimulus sets. Study 5 (N = 316) provided a partial replication and extension. Results provided consistent evidence for the exploration pathway, but more tentative evidence for the safety pathway. These findings suggest that an incorporation of person and situation factors can assist theory-development for information seeking. Part 2 provided a complementary approach to interdisciplinary dialogue by investigating how methods from cognitive neuroscience could be applied to explore possible neural bases of personality. Specifically, the machine learning technique multivariate pattern analysis was used to explore, then confirm, relations between personality and spectral power derived from electroencephalography. Study 6 (N = 174) found that agreeableness and neuroticism could be consistently decoded in particular frequencies across four testing conditions. Study 7 (N = 197) failed to replicate Study 6 in the full testing sample, but when subsequent analyses were stratified by country, agreeableness could be decoded in participants from Australia and neuroticism from participants from Germany. Caution is warranted for these latter findings given their unexpected nature and the smaller sample size of individual groups. The advantages of employing new methods are counterbalanced by a need to accept some measure of uncertainty in our inferences. However, open documentation of this complexity can spur new investigations to gain future insight into the neural bases of personality. Together, these studies emphasise the challenges, but also substantial benefits, from combining knowledge and methods from personality psychology and cognitive neuroscience to constrain existing theory, form links between research domains, and propose new avenues for research.

Persisting post-concussion symptoms (PPCS) refer to a collection of concussion symptoms (such as headache, dizziness, mood changes) that persist after the normal recovery period. In children, almost 30% of cases of concussion still have symptoms three months after injury, leading to poorer emotional wellbeing, school absences and a lower overall quality of life. It remains unclear as to what causes PPCS in children and how clinicians should diagnose the condition, however early intervention is known to be beneficial. This thesis sought to utilise novel neuroimaging techniques to gain a better understanding of the aetiology of PPCS in children and to provide clinical recommendations as to the use of neuroimaging for its diagnosis. Firstly, a systematic review and methodological critique conducted on existing neuroimaging research into concussion and mild traumatic brain injury was conducted to identify novel neuroimaging modalities which required further study. The literature was found to suffer from methodological heterogeneity, small sample sizes, and wide neuroimaging acquisition timeframes, however three novel neuroimaging modalities were highlighted as possible targets for investigation: diffusion weighted imaging (DWI), susceptibility weighted imaging (SWI), and resting state functional magnetic resonance imaging (rs-fMRI). Following on from the systematic review, the thesis investigated the aetiology of PPCS across two studies. As part of a larger study into concussion recovery, 45 children underwent neuroimaging at a two-week timepoint to assess whether there was an observable difference between children who recover normally and those who were predicted to have delayed recovery as per the Post-Concussion Symptom Inventory. No evidence of a difference was found between the groups for DWI, SWI, and rs-fMRI, with Bayesian analysis showing that there was no difference between the two groups on DWI. It was concluded neuroimaging is unlikely to successfully differentiate between normally recovering children and those who are likely to develop PPCS, given current technological constraints. In addition, it is likely that the aetiological factors of PPCS are more psychological in nature rather than arising from purely biological processes post-concussion.

In the currently fractured attitudinal landscape, many people hold extreme attitudes on important socio-political issues and frequently advocate for their attitudes. As a result of advocating for one’s own attitudes, i.e., engaging in pro-attitudinal advocacy, people may unconsciously persuade themselves (i.e. self-persuade) to polarize further. Moreover, pro- attitudinal advocacy may lead to an unwillingness to engage with those on the opposite side of the attitude spectrum. Such processes may explain polarization in our electorates over time. Given that polarization leads to disrupted social cohesion, a critical question is how we might depolarize attitudes, and encourage open communication. In this thesis, I sought to examine a candidate mechanism of depolarization: self-persuasion. More specifically, this thesis explored self-persuasion occurring during pro-attitudinal advocacy as a way of a) depolarizing attitudes and b) opening up communicative practices in ways that encourage advocates to display open communicative intentions (e.g. willingness to engage with dissimilar others). Across seven studies, participants (N = 1946) were asked to engage in online advocacy to justify their attitudes towards contemporary socio-political and moral issues, such as migration and climate-change. I explored specific factors relevant to pro- attitudinal advocacy, including meta-cognitive confidence (confidence in one’s thoughts and arguments), advocacy framing (moral versus practical framing), and style of advocacy (defending one’s position versus attacking the opposing position). Results indicate that a) low meta-cognitive confidence in one’s advocacy attempt predicts attitude depolarization and greater receptiveness to opposing views, especially if one enjoys effortful cognitive activity (Studies 1 and 2), b) compared to moral justifications, using practical justifications to support one’s attitude predicts attitude depolarization and lower intentions to proselytize, via lower expression of moral language (Studies 3-5), and c) compared to defending one’s position, attacking the opposing position predicts more open communicative practices, such as seeking attitude-inconsistent information, via heightened motivation to hold accurate worldviews (i.e. accuracy motivation; Studies 6 and 7). Interestingly, our findings suggest that although attitudes sometimes depolarize, depolarization is not a necessary pre-requisite for open communicative intentions, such as seeking attitude-inconsistent information. This suggests that pro-attitudinal advocacy may influence behavior, even if attitudes remain unchanged. Further, in addition to self-persuasion, we find other mechanisms, such as, message content and accuracy motivation, which may predict depolarization and increase open communicative practices. We find evidence to suggest that re-framing advocacy attempts, such as encouraging practical as opposed to moral justifications, may depolarize attitudes and encourage more civil discourse between dissimilar others. Overall, our findings have implications for bridging gaps between opposing groups, particularly in online communication environments.

To navigate the world safely, it is critical that we are able to rapidly evaluate and overrule about our perceptual judgements. This thesis investigated the cognitive processes which underlie two forms of decision evaluation: discrete ‘changes of mind’ (i.e. decision reversals) and continuous confidence judgements. Three specific research questions were posed and addressed. Firstly, what sources of sensory information influence the likelihood and speed with which we change our minds about a perceptual decision? Secondly, what are the moment-to-moment information processing dynamics that underlie decision reversals? And finally, can information which is seemingly extraneous to a perceptual decision, specifically the amount of physical effort invested into reporting a decision outcome, affect retrospective judgements of decision confidence? These research questions formed the basis of three studies, which make up the core empirical chapters of this thesis. Study 1 investigated whether ‘absolute’ sensory information affects change-of-mind behaviour, across two experiments. In both experiments, participants indicated which of two flickering grey squares was the brightest with a button press. Following each initial decision, the stimuli remained on screen for a brief period and participants were free to change their response. To manipulate absolute sensory evidence the overall brightness of the two squares was varied, while either their luminance difference (Experiment 1) or luminance ratio (Experiment 2) was held constant. In both experiments increases in absolute evidence led to faster, less accurate initial responses and slower changes of mind. Change-of-mind accuracy decreased when the luminance difference was held constant, but remained unchanged when the luminance ratio was fixed. To account for these findings, we examined the predictions of six models: three existing change-of-mind models and three alternative models which have previously been used to account for the effects of absolute evidence on one-off decisions. Overall, a leaky competing accumulator model best accounted for participants’ behaviour. This suggests that the biologically relevant features of leak and partial inhibition within a decision process may be important in accounting for change-of-mind behaviour. Study 2 investigated the information processing dynamics underlying initial decisions and changes of mind. In particular, this study addressed the outstanding question of whether information processed prior to a decision being made (‘pre-decisional information’) has any influence on the likelihood and speed with which that decision is later reversed. As in Study 1, participants indicated which of two flickering grey squares was the brightest. Following each decision, the stimulus briefly remained on screen and participants were free to change their response. Critically, with each screen refresh a random luminance value was added to the mean luminance value of each square. Using psychophysical reverse correlation, we then retrospectively examined the impact that this luminance noise had on participants’ decisions on a frame-by-frame basis. Strikingly, we found that even the very first frame of sensory evidence participants saw influenced the likelihood and speed of later decision reversals. This indicates that pre-decisional information can influence later change-of-mind behaviour, and challenges the most prominent model of perceptual changes of mind, the extended Diffusion Decision Model (extended DDM), which predicts a complete insensitivity to pre-decisional information. To account for our findings within the DDM framework, we developed a novel variant of the extended DDM in which initial sensory information exerts a long-lasting bias over ongoing evidence accumulation. When fit to just the behavioural response data alone, this model was able to recreate the information usage patterns we observed. This suggests that an initial 'snapshot' of sensory information may exert a long-lasting bias over later sensory evidence accumulation, thus influencing later self-corrective behavior. Finally, Study 3 investigated the effect of foregone physical effort expenditure on decision confidence judgements. In this study, a dynamic luminance discrimination task was again employed. However, participants reported their decisions by squeezing one of two hand-held dynamometers until a pre-specified force threshold was reached. To manipulate the amount of effort required to report a choice, we varied how hard participants needed to squeeze on each trial across three individually calibrated levels (low, medium, high). After each decision, participants gave a confidence rating on a continuous scale ranging from 0 (‘certainly incorrect’) to 100 (‘certainly correct’). It was found that when more effort had been invested into reporting a decision, participants were more confident that the decision was correct. Broadly put, this suggests that people are sensitive to a ‘motoric sunk cost effect’ whereby greater foregone effort expenditure leads to an inflated sense of decision confidence. Overall, these findings suggest that: a) change-of-mind decisions are sensitive to absolute as well as relative sources of sensory information, b) that initial, pre-decisional, sensory information can influence the speed and likelihood with which a decision is later reversed, and c) that additional sources of information beyond sensory evidence, specifically action dynamics, can feed into and/or modulate the processes which underlie self-evaluative behaviour. These findings are consistent with post-decisional evaluative behaviours arising out of a continued unfolding of the initial decision process, with time-varying dynamics, which receives top-down modulation from additional self-monitoring process(es).