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Intelligence is often defined as the ability of an agent to learn, adapt to its environment, and solve novel challenges. However, despite over 100 years of theoretical development (e.g., general intelligence), widespread explanatory power (up to 50% of variance in cognitive scores), and the ability of intelligence measures to predict important life outcomes such as educational achievement and mortality, the exact configuration and neural correlates of cognitive ability remain poorly understood. This dissertation aims to make progress in this pursuit by exploring how human brain structure and intelligence correlate and co-develop with each other from childhood to early adulthood (ages 5 - 22 years). This endeavour is undertaken in three large cohorts (N range: 337 - 2072), guided by theory (e.g., crystallised and fluid intelligence), and implemented using rigorous, cutting-edge quantitative methods (i.e., structural equation modelling and network science). The results of this research provide robust evidence that the brain-behaviour relationships in intelligence are complex (i.e., consists of many independent yet interacting parts) and change nonlinearly during development. The first study sought to elucidate the factorial structure and white matter substrates of child and adolescent intelligence using two cross-sectional, developmental samples (CALM: N = 551 (N = 165 neuroimaging), age range: 5 - 18 years; NKI-Rockland: N = 337 (N = 65 neuroimaging), age range: 6 - 18 years). In both samples, it was found (using structural equation modelling (SEM)) that cognitive ability is best modelled as two separable yet related constructs, crystallised and fluid intelligence, which became more distinct (i.e., less correlated) across development, in line with the age differentiation hypothesis. Further analyses revealed that white matter microstructure, most prominently of the superior longitudinal fasciculus, was strongly associated with crystallised (gc) and fluid (gf) abilities. Finally, SEM trees, which combines traditional SEM with decision trees, provided evidence for developmental reorganisation of gc and gf and their white matter substrates such that the relationships among these factors dropped between ages 7 - 8 years before increasing around age 10. Together, these results suggested that shortly before puberty marks a pivotal phase of change in the neurocognitive architecture of intelligence. The second study builds upon the first by again examining the neurocognitive structure of intelligence, this time from a network perspective. The network or mutualism theory of intelligence presupposes direct (statistical) interactions among cognitive abilities (e.g., maths, memory, and vocabulary) throughout development. Therefore, this project used network analytic methods (specifically graphical LASSO) to simultaneously model brain-behaviour relationships essential for general intelligence in a large (behavioural, N = 805; cortical volume, N = 246; fractional anisotropy, N = 165), developmental (ages 5 - 18 years) cohort of struggling learners (CALM). Results indicated that both the single-layer (cognitive or neural nodes) and multilayer (combined cognitive and neural variables) networks consisted of mostly positive, small partial correlations, providing further support for the mutualism/network theory of cognitive ability. Moreover, using community detection (i.e., the Walktrap algorithm) and calculating node centrality (absolute strength and bridge strength), convergent evidence suggested that subsets of both cognitive and neural nodes play an intermediary role 'between' brain and behaviour. Overall, these findings suggest specific behavioural and neural variables that may have greater influence among (or might be more influenced by) other nodes within general intelligence. The final study investigated the longitudinal relationships between human cortical grey matter structure and measures of decision-making, risk-related behaviours, and spatial working memory from adolescence to early adulthood (ages 14 - 22 years). In the IMAGEN study (maximum N across time points/waves = 2072), latent growth curve models were used to estimate the baseline and longitudinal associations between behavioural measures and cortical surface area, thickness, and volume. Univariate models (only behavioural or neural measures) revealed that performance in decision-making, risk-related behaviours, and spatial working memory, as well as brain structure changed nonlinearly from mid-adolescence (age 14) to early adulthood (age 22). Furthermore, bivariate models (combined behavioural and neural measures) provided evidence for adaptive reorganisation (behaviour intercept predicts changes in brain structure) but not structural scaffolding (brain structure intercept predicts changes in behaviour). Furthermore, findings suggested that there were no correlated changes between behavioural and brain structure slopes (rates of change from mid-adolescence to early adulthood). This dissertation concludes by summarising the core results, addressing key limitations, and discussing avenues for future research. Taken together, this thesis hopes to convince cognitive neuroscientists that to understand cognitive ability and its neural determinants, they (we) must work more diligently toward building coherent, rigorous, and testable neurocognitive theories of intelligence-particularly under the conceptual and analytic paradigm of complex systems.

This study was concerned with exploring young people’s experiences of engaging in individual Art Therapy sessions. An exploratory research question was formulated and addressed using a qualitative methodology. Five young adults were recruited through voluntary organisations and art therapists in private practice. Participants took part in semi structured interviews, which were analysed using Interpretative Phenomenological Analysis. Five master themes were constructed from the data: From an initial trepidation, young adults engaged with art materials, enjoying parts of the process. They felt under observation by their art therapists, and they overcame the challenge of trusting their therapist when they felt emotionally validated and understood. They made sense of their presenting difficulties through their art-making, gaining further psychological insight. They felt connected with their childhood, recalling fond memories and feeling compassion for their child self. They considered the impact of Art Therapy sessions as a learning experience. These findings highlight the need for further research to explore further the process of making sense of difficulties through art, and the therapeutic value of connecting to one’s childhood. Art Therapy can be experienced as a rewarding learning process, that helps young adults express and process their difficulties. Its benefits should be therefore communicated to referrers, service users and service developers, as it is a therapeutic mode that may offer different experiences to talking therapies.

Individuals who experience childhood trauma have profound, lasting repercussions on their psychological and physical well-being. This non-experimental correlational study’s purpose is to evaluate if childhood trauma exposure predicts undergraduate college success rates for early adults. This study is designed to examine how the mediating factors of anxiety, substance use, and self-esteem are altered after childhood trauma exposure, ultimately influencing the ability to succeed in a college setting. Four research questions drove this study: (a) What is the relationship between the frequency of complex childhood trauma and college success rates?, (b) How does anxiety mediate the relationship between the frequency of complex trauma and college success rate?, (c) How does the rate of substance use mediate the relationship between frequency of complex trauma and college success rate?, and (d) How does the rate of self-esteem mediate the relationship between the frequency of complex trauma and college success rate? Participants were recruited from Liberty University’s undergraduate student population. Data was collected via an online questionnaire and was analyzed using IBM SPSS statistics software. Significant findings indicate a negative correlational relationship between childhood trauma exposure and undergraduate academic success. It was also found that as drug use increased, college success decreased. Finally, it was found that self-esteem is a mediating factor between childhood trauma and undergraduate success rates. This research highlights the importance of implementing interventions to help individuals who have been exposed to childhood trauma succeed in an academic setting while also overcoming complex repercussions.

This thesis examines the relationship between immigrant generation and early adulthood incorporation into higher education and work. Using data from the High School and Beyond Sophomore cohort I explore when and where disparities between the children of immigrants and their native-born, native parent peers emerge. I find that the relationship between immigrant generation and post-secondary education enrollment and early adulthood employment varies by gender. Furthermore, it is at the entry points into higher education and work that disparities emerge. This research indicates that entry into social institutions should be considered as likely sites of inequality and that processes of incorporation may be gendered.

Sociological and criminological research has emphasized the role of delinquent peers and romantic partners on involvement in delinquent activities. In this study, I analyzed the effect of delinquent domains in late adolescence on criminal activity in early adulthood. I hypothesized that individuals with multiple delinquent domains would report higher levels of criminal activity compared to those with one or no delinquent domains. I also hypothesized that for those with one delinquent domain, differences exist in levels of criminal activity between those reporting delinquent peers or delinquent romantic partners. Finally, I hypothesized that the delinquent domains on criminal activity may differ for young adult men and women. Drawing on the longitudinal data of the Toledo Adolescent Relationships Study (n = 801), I analyzed the effect of delinquent social domains in adolescence on criminal behavior in young adulthood. Having delinquent domains during late adolescence is significantly related to engagement in criminal activity during young adulthood, net of control variables. In addition, having both highly delinquent peers and romantic partners, compared with just one delinquent affiliation, was related to higher levels of criminal activity. The effect of peers on criminal activity was stronger than the effect of delinquent romantic partners. Further, the association between delinquent domains and criminal activity was different for men and women with both highly delinquent peers and romantic partners during late adolescence. My findings offer support for the “long reach” of late adolescent delinquent domains on subsequent criminal activity.

Early adulthood is a period when individuals begin to obtain major social statuses, such as finishing school, starting a full-time job, getting married, or becoming a parent. How these social statuses may influence the quality of sibling relationships has rarely been examined. Sibling relationships are common, likely some of the longest relationships most individuals who have siblings will experience, and can be a source of support throughout the life course. Thus, it is important to decipher factors that influence sibling relationship quality. This thesis project uses matched sibling dyads data from the sibling sample in Wave III of the National Longitudinal Study of Adolescent to Adult Health (N = 1,451), to examine the associations between social statuses—education, employment, marriage or cohabitation, and parenthood—and five aspects of sibling relationship quality, including emotional closeness, conflict, direct contact, indirect contact, and turning to one’s sibling for help or advice, among respondents aged 18 to 26. Supporting the time demands perspective, the respondents’ or the siblings’ marriage or cohabitation is related to less direct or indirect contact and fewer fights between siblings. When one sibling is in college, the other sibling tends to report less direct contact. In contrast, supporting the role expansion perspective, older siblings’ parental status is related to younger siblings’ reports of more contact and emotional closeness with the sibling. Those who have a college degree are more likely than those without it to have more indirect contact with their siblings. These findings suggest interconnectedness of siblings’ lives during the transition to adulthood.

Using data from a nationally representative study on adolescent health (Add Health), this study examined the direct and interrelated associations of emotional support from four key providers (mother, father, teacher, and peers) and adolescent psychosocial outcomes. These associations were examined at three time points, following participants from early adolescence to early adulthood. The study also explored how the influences of various support relationships change during the transition from early adolescence to early adulthood and how such changes affect outcomes. Support from mother, father, teacher and peers were linked to improvements in different domains of adolescent outcomes, with the exception of peer supports’ link with increased delinquent behavior. The perceived support from the sources examined was also predictive of psychosocial functioning across time. This study also found fathers’ perceived support to be predictive of more of the psychosocial domains examined than mothers, indicating that father support has more substantial influence than previously thought. Further, the positive associations among adolescent outcomes and teacher support were not found to be as domain-specific for adolescents as espoused in the literature. In addition, when multi-group models were used to examine age differences in associations between perceived support and adolescent outcomes, middle adolescence appeared to be the period when adolescents are most receptive to all the support relationships examined. Adolescents’ psychosocial functioning was also found to be predictive of different sources of perceived support.

There is considerable research demonstrating the link between depression and interpersonal stress. This literature has included support for the phenomenon of stress generation, or the tendency for individuals with depression histories to have higher levels of stress in their lives, particularly interpersonal stressors, even after depression remits. Currently missing from the existing literature, but supported by multiple psychological theories and research on constructs related to depression, is the possibility that individuals prone to depression may self-select into maladaptive romantic partnerships that promote stress and exacerbate depression. The current project sought to explore whether depression portends risk for choosing romantic partners with higher levels of psychopathology or disordered personality traits. This question was explored in two complementary studies. Study 1 utilized a longitudinal, community sample of 252 individuals followed from birth to early adulthood with romantic partners at age 20. Results indicated that individuals with higher levels of depressive symptoms at age 15 had romantic partners by age 20 with higher levels of personality disorder symptoms. Insecure attachment mediated this relationship. Partner personality pathology, in turn, marginally predicted increases in depressive symptoms 2 to 5 years later. Study 2 explored the role of depression in the mate selection process by using a mock online dating laboratory paradigm in which college-aged women rated hypothetical romantic partners based on fabricated dating profiles. Some profiles included antisocial personality disorder traits. Results revealed that current depressive symptoms and major depression history indirectly predicted lower initial interest in "antisocial" profiles via lower self-esteem and lower perceived similarity to these individuals, respectively. However, when participants were later asked to imagine that an "antisocial" individual was interested in dating them, depressive symptoms predicted greater positive change in interest in this individual and a greater likelihood of changing an initial refusal to date this individual to a positive response. Findings from both studies indicate that depression plays a role in the mate selection process and can have detrimental consequences. Future research would benefit from further exploring mediators of the relationship between depression and choosing problematic partners and the role of partner characteristics in the cycle of stress and depression.

The heart of this thesis is six personal essays reflecting on experiences spanning from the author's late teens to early thirties. Although they recall the author's personal experiences learning about her relationship to others, as well as her relationship to herself, the essays also deal with universal commonplace subjects, such as work, love, attraction, and friendship. The author attempts to offer authentic human experiences where all readers can find something that resonates with them and inspires them to reflect on their own lives.

Adjustment, particularly in adulthood, is a vague concept discussed among researchers. Most often researchers only consider lack of involvement in problem behavior as criteria for positive adjustment. Furthermore, it is unclear what factors influence the likelihood of adjustment and the influence of race on these factors is unknown. The current study proposed a composite of male adult adjustment that considers what the Wellness Model terms the “wholeness” of an individual. In addition, adolescent predictors of adult adjustment and the influence of race on factors influencing adjustment were examined in a longitudinal sample of 481 males. Results revealed 4 profiles of adjustment: 1 profile that included individuals who were overall adjusted, 2 profiles that included individuals who were moderately adjusted, and 1 profile of individuals who were maladjusted. The majority of the sample was identified as adjusted in that they were financially responsible, did not have psychological problems, engaged in little to no acts of delinquency, and acknowledged at least adequate social support. Note, however, that these individuals did engage in some substance use. The smallest profile of individuals was those who were maladjusted in that they engaged in excessive delinquency, used both drugs and drank alcohol heavily, and lacked a positive support system. However these individuals were also absent of psychological problems and were financially responsible. Findings also uncovered predictors of adjustment, such that high levels of depression, physical punishment, and poor relationships with peers were associated with only moderate levels of adjustment regardless of race. Furthermore, racial differences in predictors of adjustment were found. Anxiety and parent/child communication were associated with only moderate adjustment for African American but not Caucasian males. In contrast, mother’s arrest and peer delinquency were associated with only moderate adjustment for Caucasian American but not African American males. Recommendations for prevention and intervention strategies are discussed.

The aim of this project was to investigate the impact of language proficiency (represented in first and second language) on working memory capacity. A sample of 100 college students from Virginia Tech University completed an on-line survey, performed 2 computer-based working memory capacity tasks (the OSPAN and the Letter Rotation) and had their first language (L1) as well as their second language (L2) proficiency tested. All participants were classified on a five-point likert scale from "poor" to "excellent". Verbal WMC (as measured by OSPAN) was associated with L2 proficiency. However, the L2 "excellent" group did not differ in their OSPAN from the remaining four groups of L2 proficiency classification. No correlation was found between the two WMC tasks.