Executive function (EF) is a central aspect of cognition that undergoes significant changes in early childhood. Changes in EF in early childhood are robustly predictive of academic achievement and general quality of life measures later in adulthood. I develop a dynamic neural field (DNF) model which provides a process-based account of behavior and developmental change in a key task used to probe the early development of executive function--the Dimensional Change Card Sort (DCCS) task. In the DCCS, children must flexibly switch from sorting cards either by shape or color to sorting by the other dimension. Typically, 3-year-olds, but not 5-year-olds, lack the flexibility to do so and perseverate on the first set of rules when instructed to switch. In Study 1, I use the DNF model to integrate behavioral and neural processes by simulating hemodynamics associated with the early emergence of flexible rule-use. I then test predictions of the model using near-infrared spectroscopy. In Study 2, I develop a DCCS that can be used with adults that sheds light on key aspects of the task as they have been revealed with children. Using fMRI, a pattern of behavioral and neural effects shed light on the central processes involved in flexible rule-use. These two studies demonstrate that performance emerges as a property of system-wide interactions and that common neurocognitive effects .can be found between childhood and adulthood.

Data on standardized tests is often used to advocate for the inclusion of music programs in secondary education curriculum. There have been studies that claim to identify a relationship between music participation and higher earned test scores; however, correlation does not necessarily equate to causation. The argument between whether music instruction improves student testing ability or if higher achieving students are attracted to music courses is still prevalent within the music education domain. Executive function represents the processes within the brain that encompass a number of cognitive ability processes used in the transfer of knowledge. These processes are essential to progression and success in education (Caine & Caine, 2006; Chan, et. al., 2008). Research demonstrates that music instruction has the capacity to enhance various executive function processes in young students with previous music instruction and individualized violin training (Bugos, 2010; Ho et al., 2003; Chan et al., 1998). The purpose of this study was to evaluate the effects of secondary music instruction, specifically in the band setting, on executive function processes of processing speeding and working memory. 40 high school students, 20 students who had received previous band instruction and 20 who had not received previous band instruction ages 13 to 18, completed various cognitive and musical assessments to gauge musical ability and cognitive function (measuring attention, working memory, and processing speed). Students from both groups were paired using the Wechsler Abbreviated Intelligence Scale. Analysis of the results demonstrated that students who received prior band instruction demonstrated enhanced processing speed and working memory indices, as well as increased attention abilities.

<p>Deficits in higher order cognitive processes such as inhibitory control and working memory (WM), grouped under the term of executive function (EF), have been shown to constitute one important component of the complex neuropsychology of Attention Deficit Hyperactivity Disorder (ADHD). The aim of the present thesis was to examine EF in relation to ADHD, with primary focus on structure (i.e., dimensions) and developmental change. Rooted in the developmental and dimensional perspectives of ADHD, which propose that the disorder represents the extreme of or quantitative delays in traits that are present throughout the general population, four studies (I-IV) based on non-clinical and clinical samples of children at different developmental levels were conducted.</p><p>Together, the results from Study I-IV suggest that inhibitory control and WM are important components of EF in typically developing children as well as in relation to ADHD symptoms. Of particular interest are the findings from Study II, III, and IV, showing that inhibitory control and WM seem to be of different importance depending on the child’s age. More specifically, the non-clinical and clinical studies suggest that inhibitory control and WM are important in predicting ADHD symptoms, with deficits in inhibitory control primarily being associated with ADHD symptoms for preschool and younger elementary school-aged children, whereas deficits in WM are associated with ADHD symptoms for older elementary school-aged children. </p><p>In conclusion, the results of the present thesis are consistent with Barkley’s (1997) developmental prediction concerning the relation between EF and ADHD, which suggests that impaired inhibitory control is an early developmental precursor to or a factor that “sets the stage” for deficits in more complex EFs such as WM. The home taking message from the present thesis is that age matters not only in the behavioral, but also in the neuropsychological manifestation of ADHD. To our knowledge, these findings are among the first to show that age is an important factor that should be taken into account in future ADHD research, theory, and treatment.</p>

Current theoretical models of ADHD (i.e., Disinhibition Model: Barkley, 1997; Working Memory Model: Rapport et al., 2001) conceptualize ADHD as the disorder of executive function (EF) with some variation in their emphases on particular components of the broadly-defined EF (e.g., working memory vs. inhibition) and in their postulated relationships with ADHD symptoms. Although these models provide systematic accounts of the manifestation of ADHD, they have not been extensively tested from an empirical standpoint. Moreover, despite the fact that ADHD is highly comorbid with other additional conditions such as learning and behavioral problems and EF deficits are found in individuals with these conditions as well as in those with ADHD, current EF models have not specified the developmental relationship between ADHD and its comorbid conditions. This study was: (1) to examine the extent to which two current models of ADHD are supported in a sample of 102 adults; (2) to present an ??integrated?? model by combining two current models of ADHD and linking them to recent research findings on two common comorbid conditions with ADHD (i.e., reading difficulty and substance abuse); and (3) to test and revise such an integrated model in the light of data using a latent variable analysis. Major findings provided a strong support for the Working Memory Model with a lesser degree of support for the Disinhibition Model. Preliminary evidence of working memory as the primary deficit in ADHD was also obtained in the present sample. Finally, the integrated EF model and its revised model (final model) demonstrated a very good fit to the data. These findings suggest that the integrated model provides a unified account of how EF deficits contribute to the manifestation of ADHD symptoms and comorbid conditions with ADHD. Given some limitations (e.g., sample size and scope) of the present study, current findings need to be replicated.

Deficits in higher order cognitive processes such as inhibitory control and working memory (WM), grouped under the term of executive function (EF), have been shown to constitute one important component of the complex neuropsychology of Attention Deficit Hyperactivity Disorder (ADHD). The aim of the present thesis was to examine EF in relation to ADHD, with primary focus on structure (i.e., dimensions) and developmental change. Rooted in the developmental and dimensional perspectives of ADHD, which propose that the disorder represents the extreme of or quantitative delays in traits that are present throughout the general population, four studies (I-IV) based on non-clinical and clinical samples of children at different developmental levels were conducted. Together, the results from Study I-IV suggest that inhibitory control and WM are important components of EF in typically developing children as well as in relation to ADHD symptoms. Of particular interest are the findings from Study II, III, and IV, showing that inhibitory control and WM seem to be of different importance depending on the child’s age. More specifically, the non-clinical and clinical studies suggest that inhibitory control and WM are important in predicting ADHD symptoms, with deficits in inhibitory control primarily being associated with ADHD symptoms for preschool and younger elementary school-aged children, whereas deficits in WM are associated with ADHD symptoms for older elementary school-aged children. In conclusion, the results of the present thesis are consistent with Barkley’s (1997) developmental prediction concerning the relation between EF and ADHD, which suggests that impaired inhibitory control is an early developmental precursor to or a factor that “sets the stage” for deficits in more complex EFs such as WM. The home taking message from the present thesis is that age matters not only in the behavioral, but also in the neuropsychological manifestation of ADHD. To our knowledge, these findings are among the first to show that age is an important factor that should be taken into account in future ADHD research, theory, and treatment.

Higher-order cognitive functions, such as executive function (EF) and intelligence, are crucial to the everyday functioning of human beings. Gaining knowledge about these functions is important for our general understanding of human nature as well as for our ability to help those who may not develop these processes optimally. The present thesis focused particularly on the EF component working memory (WM), described as the ability to maintain informa-tion in consciousness during short time periods with the purpose of using that information in complex cognition. The major aims of the thesis were to increase our understanding of higher-order cognition in children as well as of deficiencies in intelligence found in children with Attention Deficit Hyperactivity Disorder (ADHD). We approached these aims by studying the interrelations among EF-related components in terms of their independent contributions to intellectual functioning. We also studied whether the lower intelligence in children with ADHD was mediated by fundamental EF-related components or whether these deficiencies went beyond the weaknesses in these specific cognitive functions. Interpreting the present data, we suggest that intellectual functioning in children is best viewed as representing a system of primarily independent parts that may be accompanied by an overarching common mechanism. The multiple components involve, but are surely not limited to, WM functions, inhibitory functions, sustained attention, and processing speed. One of these functions, WM, was found to be further partitioned into domain-specific executive WM processes and domain-specific short-term storage processes, all of which constitute important aspects of higher-order cognitive functioning. We have further learned that deficits in fluid intelligence in children with ADHD may entail more than weaknesses in specific central cognitive functions. This additional deficit is cautiously interpreted as involving supe-rior executive attention functions setting the stage for the development and integration of the EF system as well as the “intelligence system”.

Many people who sustain traumatic brain injuries (TBI) have poor psychosocial outcomes. Previous research has indicated that poor outcomes are related to the use of avoidant coping following TBI, although the mechanisms of this relationship are not clear. The major pathological consequence of TBI is damage to the frontal lobes and/or their connections, resulting for most people in executive and/or affective dysfunction. The purpose of this dissertation study was to delineate the neuropsychological, psychiatric, personality and physiological mechanisms of avoidant coping following TBI. Controls and people with TBI completed the Baycrest Psychosocial Stress Test (BPST), where coping behaviour was observed directly, and physiological measures were recorded. Participants also completed a neuropsychological test battery, and a series of questionnaires assessing coping, psychiatric status, personality and outcomes. There were no significant differences between groups in self reported coping. However, the control and mild TBI group engaged in more planful than avoidant behaviour on the BPST. As a group, individuals with moderate-to-severe injury, in contrast, engaged in more avoidant than planful behaviour. However, analysis of individual differences in coping behaviour within the moderate-to-severe group revealed a bimodal distribution, allowing classification of people in this group as ‘planners’, or ‘avoiders’ (this distribution was not evident in the mild TBI group). Within the moderate-to-severe group, planners had better executive function, were more reactive to stress (psychologically and physiologically), performed better on the speech task during the BPST, and had greater return to productivity. However, planners also had worse psychosocial outcomes as compared to the avoiders. This was the first study, to the author’s knowledge, to examine coping behaviour during a simulated real-world stress test. Results indicate that behavioural measures of coping, such as the BPST, are more sensitive to changes in coping post TBI than are self and significant other reported questionnaires. Results also demonstrate that executive function and psychological and physiological reactivity are important factors that contribute to coping following moderate-to-severe TBI. These data raise important questions about the challenges of targeting coping through rehabilitation.

Commonly employed executive function measures may be of limited use due to their modest ecological validity. A novel task was developed - the Multitasking in the City Test (MCT) - in an attempt to improve ecological validity. The MCT involves task demands that resemble the demands of everyday activities. In study one, healthy participants were recruited in order to explore ‘normal’ performance on the MCT and its relationship with other cognitive measures. The MCT showed poor associations with executive tests and significant correlations with non-executive tests. This suggested the MCT may evaluate executive functioning in a different way from other executive measures such that it does not simply measure component executive processes but the integration of these components into meaningful behaviour. Patients with stroke and traumatic brain injury were recruited for study two to further explore the ecological validity and MCT performance characteristics. Only the MCT and a semantic fluency task demonstrated good ecological validity via significant relationships with a behavioural rating scale. Patients and normals made qualitatively similar types of errors although patients made these errors more frequently. Patients demonstrated better planning ability but completed fewer tasks than normals on the MCT. This discrepancy was attributed to impaired initiation. In study three, the MCT and verbal fluency tasks were administered to brain-injured individuals both pre- and post-executive function rehabilitation to evaluate their utility as treatment outcome measures and to assess ecological validity via a different behavioural rating scale from the one used in study two. Strategies trained during treatment generalized to MCT but not verbal fluency performance. Both MCT and semantic fluency performance were found to have good ecological validity. Overall, the findings from this research project suggest the MCT and semantic fluency tasks have good ecological validity. They further suggest that several common executive function measures lack adequate ecological validity and may not be predictive of real world behaviour. Moreover, these results support the concept of an executive function ‘system’ that can be fractionated into a variety of executive processes and that impairments in one process (e.g., initiation) can exist alongside intact functioning in other processes (e.g., planning).

Many people who sustain traumatic brain injuries (TBI) have poor psychosocial outcomes. Previous research has indicated that poor outcomes are related to the use of avoidant coping following TBI, although the mechanisms of this relationship are not clear. The major pathological consequence of TBI is damage to the frontal lobes and/or their connections, resulting for most people in executive and/or affective dysfunction. The purpose of this dissertation study was to delineate the neuropsychological, psychiatric, personality and physiological mechanisms of avoidant coping following TBI. Controls and people with TBI completed the Baycrest Psychosocial Stress Test (BPST), where coping behaviour was observed directly, and physiological measures were recorded. Participants also completed a neuropsychological test battery, and a series of questionnaires assessing coping, psychiatric status, personality and outcomes. There were no significant differences between groups in self reported coping. However, the control and mild TBI group engaged in more planful than avoidant behaviour on the BPST. As a group, individuals with moderate-to-severe injury, in contrast, engaged in more avoidant than planful behaviour. However, analysis of individual differences in coping behaviour within the moderate-to-severe group revealed a bimodal distribution, allowing classification of people in this group as ‘planners’, or ‘avoiders’ (this distribution was not evident in the mild TBI group). Within the moderate-to-severe group, planners had better executive function, were more reactive to stress (psychologically and physiologically), performed better on the speech task during the BPST, and had greater return to productivity. However, planners also had worse psychosocial outcomes as compared to the avoiders. This was the first study, to the author’s knowledge, to examine coping behaviour during a simulated real-world stress test. Results indicate that behavioural measures of coping, such as the BPST, are more sensitive to changes in coping post TBI than are self and significant other reported questionnaires. Results also demonstrate that executive function and psychological and physiological reactivity are important factors that contribute to coping following moderate-to-severe TBI. These data raise important questions about the challenges of targeting coping through rehabilitation.

Commonly employed executive function measures may be of limited use due to their modest ecological validity. A novel task was developed - the Multitasking in the City Test (MCT) - in an attempt to improve ecological validity. The MCT involves task demands that resemble the demands of everyday activities. In study one, healthy participants were recruited in order to explore ‘normal’ performance on the MCT and its relationship with other cognitive measures. The MCT showed poor associations with executive tests and significant correlations with non-executive tests. This suggested the MCT may evaluate executive functioning in a different way from other executive measures such that it does not simply measure component executive processes but the integration of these components into meaningful behaviour. Patients with stroke and traumatic brain injury were recruited for study two to further explore the ecological validity and MCT performance characteristics. Only the MCT and a semantic fluency task demonstrated good ecological validity via significant relationships with a behavioural rating scale. Patients and normals made qualitatively similar types of errors although patients made these errors more frequently. Patients demonstrated better planning ability but completed fewer tasks than normals on the MCT. This discrepancy was attributed to impaired initiation. In study three, the MCT and verbal fluency tasks were administered to brain-injured individuals both pre- and post-executive function rehabilitation to evaluate their utility as treatment outcome measures and to assess ecological validity via a different behavioural rating scale from the one used in study two. Strategies trained during treatment generalized to MCT but not verbal fluency performance. Both MCT and semantic fluency performance were found to have good ecological validity. Overall, the findings from this research project suggest the MCT and semantic fluency tasks have good ecological validity. They further suggest that several common executive function measures lack adequate ecological validity and may not be predictive of real world behaviour. Moreover, these results support the concept of an executive function ‘system’ that can be fractionated into a variety of executive processes and that impairments in one process (e.g., initiation) can exist alongside intact functioning in other processes (e.g., planning).