Mindfulness-based meditation practices involve various attentional skills including the ability to sustain and focus ones attention. During a simple mindfulness based breath awareness meditation, sustained attention is required to maintain focus on the breath while meta-cognitive awareness and executive control are required to detect and correct mind wandering. The purpose of this thesis was to investigate whether a simple, mindfulness based breath awareness meditation, administered over a short period to meditation naïve individuals could modulate core attentional functions and associated task related neural activity. Two longitudinal randomised control studies were conducted. The aim of the first study was to establish if said modulations were possible in a sample of healthy adults, meeting a current research need for longitudinal evidence in this field and providing important information regarding a potential mechanism for the salutary effects widely observed from the use of mindfulness based interventions. It was found that short term engagement with a mindfulness based breath awareness meditation can modulate core attentional functions and task related neural activity, with specific modulations found in electrophysiological markers of sustained attention to the goal/task at hand and perceptual stimulus discrimination. In line with current theoretical models it is argued that modulations to such core attentional processes following short term training may provide a platform upon which mindfulness related salutary effects are built. The second study was designed to establish if such modulations were possible in older adults. It is argued that mindfulness training may have utility for increasing cognitive reserve, a potential mechanism by which age related declines in cognitive functions may be mitigated. It was found that both behavioural and electrophysiological markers of core attentional functions were modulated following 8 weeks mindfulness training but not following a matched active control group condition (simple brain training exercises). The reviewed extant evidence and findings of this study suggest that mindfulness meditation may enhance cognitive reserve through the repeated activation of attentional functions and associated neural activity during practice and are consistent with recent theoretical models of cognitive reserve. The potential for mindfulness training to positively modulate core attentional functions in older adults and to potentially impact cognitive ageing demands further investigation.

Eines der ungelösten Probleme menschlicher Kognition ist S. Monsell (1996) zufolge, wie genau sprachliche Aufgabeninstruktionen in Aufgabenrepräsentationen übersetzt werden, die instruiertes Verhalten steuern. Die vorliegende Arbeit versucht, Licht auf einen Aspekt dieser Frage zu werfen. Die spezifische Frage ist, ob und wie die Details der Instruktionen von Antworten in einfachen manuellen Zweifachwahlaufgaben die Kodierung und die Prozesse beeinflussen, die üblicherweise mit "Antwortselektion" assoziiert werden, einem Verarbeitungsstadium, das als zentral für die willkürliche Steuerung von Handlungen angesehen wird. Thematisch liefert die Dissertation somit einen Beitrag zu der Frage nach den kognitiven Grundlagen der Steuerung von Willkürhandlungen. Unter der Annahme, dass die spezifischen Inhalte sprachlicher Antwortinstruktionen die Antwortkodierung determinieren, ist zu erwarten, dass identische Aufgaben bei unterschiedlicher Antwortinstruktion unterschiedlich bearbeitet werden. Diese Vorhersage wurde mittels zweier experimenteller Ansätze in fünf Experimenten überprüft, in denen linke und rechte Tastendruck-Reaktionen entweder räumlich (als "linke" vs. "rechte" Taste) oder farblich (als "blaue" vs. "grüne" Taste) instruiert wurden. Es wurde untersucht, welchen Einfluss Antwortinstruktionen auf zwei Arten von Kompatibilitätseffekten haben. In den ersten 3 Experimenten wurde ein Doppelaufgabenparadigma gewählt, das überlappende vs. nicht-überlappende Antworten auf einer manuellen und einer zeitgleich ausgeführten verbalen Aufgabe erforderte. Die verbale Aufgabe erforderte ebenfalls entweder "links"- und "rechts"- oder "blau"- und "grün"-Antworten. Wenn die Antworten beider Aufgaben räumlich (Experiment 1) oder farblich (Experiment 2) instruiert wurden, waren kompatible Antworten (z. B. verbale "blau"-Reaktionen gefolgt von blauen Tastenreaktionen) in beiden Aufgaben schneller als inkompatible. Wenn jedoch die verbale Aufgabe "links"- und "rechts"-Reaktionen verlangte, während die Tasten der manuellen Aufgabe farblich instruiert wurden, zeigten sich keine Kompatibilitätseffekte. Das 4. und 5. Experiment dieser Arbeit erweitern die Doppelaufgabenexperimente dahingehend, dass der Einfluss der gleichen Antwortinstruktionsmanipulation auf den "Simon-Effekt" (schnellere Antworten bei Korrespondenz als bei Inkorrespondenz zwischen Antwortposition und irrelevanter Stimulus-Position) mit Hilfe einer Aufgabe untersucht wurde, in der linke und rechte Tastenreaktionen willkürlich zentral dargebotenen Stimuli (Buchstabenidentität) zugeordnet wurden. Go/no-go Signale, die zufällig an unterschiedlichen Positionen erschienen, gaben an, ob reagiert werden sollte oder nicht. Während ein Simon-Effekt bei räumlicher Antwortinstruktion in Experiment 4 beobachtet werden konnte, führten Farbinstruktionen der Antworttasten in Experiment 5 zu einer signifikanten Reduktion des Effekts. Zusammengenommen legen diese Ergebnisse nahe, dass die in der Antwortinstruktion genutzten Antwort-"Label" direkt bestimmen, welche Codes zur Reaktionssteuerung genutzt werden, und dass nicht-räumliche Antwortkodierung bei nicht-räumlicher Antwortinstruktion dominiert. Die Implikationen der Befunde für aktuelle Kodierungstheorien zur Erklärung von Kompatibilitätseffekten werden diskutiert und in Bezug gesetzt zu allgemeineren Theorien und Fragen zur willkürlichen Steuerung von Verhalten und zu den Bedingungen von Automatizität. / According to Monsell (1996), one of the 'unsolved mysteries of mind' is how exactly verbal task instructions are translated into, and are used to control behavior. The present dissertation attempts to shed some light on one aspect of this mystery, namely on how the wording of task instructions affects the codes and processes commonly associated with response selection, a processing 'stage' assumed to be central in action control. The main question is whether or not the response labels used in the instructions of manual two-choice responses affect how responses are coded and accessed. If instruction determines response coding, then it should be possible to demonstrate that identical tasks are performed differently if response instructions differ. In five experiments, I manipulated response instructions for spatially organized keypress responses. Specifically, I instructed left and right keypresses on a manual task either as left vs. right or as blue vs. green keypresses and tested whether such variations in response instructions affect two different types of compatibility effects. The first set of experiments (Experiments 1-3) used a dual task procedure that, in addition to the manual task, required either "left" vs. "right" or "blue" vs. "green" verbalizations on a concurrently performed verbal task. When responses on both the manual and the verbal task were instructed in terms of location (Experiment 1) or color (Experiment 2), then compatible responses on the two tasks (e.g., "blue" verbalizations followed by a blue keypress) were faster than incompatible responses. However, when the verbal task required "left" vs. "right" responses whereas manual keypresses were instructed as blue vs. green (Experiment 3), then no compatibility effects were observed. The second set of experiments (Experiments 4 and 5) extended these findings by employing the same response-instruction logic to a Simon-like task, in which left and right keypress responses were arbitrarily mapped to centrally presented stimuli (letter identity). Go/No-go signals that varied in location indicated whether the prepared response was to be executed or not. Color instructions of the response keys (Experiment 5) significantly reduced the Simon effect (i.e., faster responses when response location and irrelevant Go/No-go location correspond) observed under spatial response instructions (Experiment 4). Taken together, these results suggest that response labels used in the instruction directly determine the codes that are used to control responding, and that non-spatial coding can override spatial coding under non-spatial response instructions. The findings are discussed with respect to their relevance for contemporary coding accounts of compatibility and more general theories of intentional control and automaticity.

Dans le contexte actuel du vieillissement de la population, il importe de s’intéresser aux changements qui surviennent avec l’avancement en âge. Le vieillissement s’accompagne de modifications pour différentes fonctions cognitives, dont la mémoire de travail (MdeT), un système permettant le maintien temporaire et la manipulation d’une petite quantité d’informations. Les travaux de cette thèse portent sur le vieillissement normal de la MdeT et des fonctions de contrôle attentionnel (FCA) qui la sous-tendent (l’alternance, l’inhibition et la mise à jour). D’abord, la première étude (Chapitre II) visait à préciser l’effet du vieillissement normal sur la MdeT et sur chacune des FCA qui la sous-tendent. Elle avait également pour but d’identifier les FCA qui contribuent à la réalisation de différentes tâches de MdeT, et si cette contribution diffère selon le groupe d’âge. Des tâches mesurant chacune des FCA ainsi que des tâches de MdeT ont été administrées à des personnes âgées et à des jeunes adultes. Les analyses contrôlant pour le ralentissement cognitif ont révélé que les habiletés d’alternance et de mise à jour sont préservées chez les personnes âgées, mais que l’inhibition est atteinte comparativement aux jeunes adultes. Les analyses ont également montré que l’impact du vieillissement sur la MdeT dépend de la tâche utilisée. Enfin, les résultats ont indiqué que la contribution des FCA à la MdeT dépend à la fois de la tâche de MdeT et du groupe d’âge. En particulier, la mise à jour contribue davantage à la MdeT des personnes âgées qu’à celle des jeunes, ce qui pourrait refléter une tentative de compensation. La seconde étude (Chapitre III) avait pour objectif de caractériser la variabilité interindividuelle au niveau des FCA, pour les personnes âgées et pour les jeunes adultes. Des analyses hiérarchiques en grappes réalisées sur les habiletés d’alternance, d’inhibition et de mise à jour, ont permis de déterminer si différents profils de contrôle attentionnel étaient présents. L’étude cherchait également à déterminer si les individus appartenant à des profils de contrôle attentionnel distincts diffèrent quant à certaines variables intellectuelles ou de santé. Les analyses ont mis en évidence trois profils de contrôle attentionnel distincts parmi les personnes âgées, l’inhibition étant une FCA critique pour distinguer entre les trois sous-groupes. Trois profils de contrôle attentionnel ont également été identifiés chez les jeunes adultes, et ces profils étaient caractérisés par moins de variabilité intra-individuelle que ceux des âgés. Les analyses ont par ailleurs montré que les profils de contrôle attentionnel se distinguent sur certaines variables intellectuelles et de santé. Les implications théoriques et cliniques de ces résultats seront discutées en fin de thèse (Chapitre IV). / As the population is aging, it is increasingly important to study the changes that occur with advancing age. Normal aging is characterized by changes in various cognitive functions, such as working memory (WM), a limited capacity system that temporarily holds and manipulates a small quantity of information. The work presented in this thesis focused on the normal aging of WM and of the attentional control functions (ACFs) that underlie this system (shifting, inhibition, and updating). The first study (Chapter II) aimed at exploring the impact of normal aging on WM and on each of the ACFs. We also sought to determine which ACFs contribute to performance on different WM tests, and whether age group has an impact on those contributions. Tasks measuring each ACF as well as WM tasks were administered to healthy older adults and to younger adults. The analyses controlling for cognitive slowing revealed that older adults’ shifting and updating abilities are preserved, but that their inhibition abilities are impaired compared to younger adults. Moreover, the impact of normal aging on WM is task-dependent. The results also indicated that the relative contribution of the ACFs to WM depends on both the WM task used and the age group. In particular, older adults relied more than younger adults on updating to perform WM tasks, which might reflect a compensation attempt. The second study (Chapter III) aimed at characterizing interindividual variability in the ACFs of both older and younger adults. Cluster analyses were performed on the shifting, inhibition, and updating abilities, in order to determine whether different attentional control profiles were present. This study also explored whether the individuals that belonged to distinct attentional control profiles differed as to intellectual and health variables. The analyses revealed three attentional control profiles among older adults, and inhibition was the ACF for which the three profiles differed the most. Three attentional control profiles were also identified among younger adults, and their profiles were characterized by less intra-individual variability than those of older adults. The results also showed that individuals belonging to different attentional control profiles differed on some intellectual and health variables. The theoretical and clinical implications of those findings are discussed in Chapter IV.

Executive control is a vital cognitive function that facilitates the focussing and shifting of attention, planning and working towards a goal, ignoring distractions, and flexibly responding to novel situations. Disruptions to executive control are seen in many psychiatric and neurodegenerative disorders, as well as healthy ageing, which can be profoundly detrimental. Despite having many effective and well-validated methodologies for detecting and quantifying these deficits, there are very few treatments — pharmacological or otherwise — for ameliorating executive dysfunction. This lack of progress can partly be blamed on difficulties associated with identifying drugs that enhance cognition in preclinical research. The work in this thesis aimed to expand our understanding of executive dysfunction — as well as the tasks that measure it — in rats. In results presented in chapter three, middle-aged rats demonstrated impaired reversal learning on the standard attentional set-shifting task, but this was treatable with a novel drug targeting the N-methyl-D-aspartate receptor. The age impairments seen in this experiment were similar to those previously found in young rats with orbital prefrontal cortex (OFC) lesions. The results of chapter four expanded on this similarity to show that, along with reversal deficits, young OFC-lesioned rats are impaired at forming attentional sets when tested on a modified task. In chapter five, another modified set-shifting task revealed that middle-aged rats also suffer from impaired set-formation, but their reversal learning impairments only manifest before attentional set has been formed — not after. Finally, in chapter six, the putative cognitive enhancer modafinil was found to exacerbate middle-aged rats' reversal learning deficit, but it also enhanced their subsequent ability to form attentional set. These experiments reveal that modifying the rat attentional set-shifting task can sometimes make it a more effective tool for testing cognitive enhancers in preclinical settings.

Dans le contexte actuel du vieillissement de la population, il importe de s’intéresser aux changements qui surviennent avec l’avancement en âge. Le vieillissement s’accompagne de modifications pour différentes fonctions cognitives, dont la mémoire de travail (MdeT), un système permettant le maintien temporaire et la manipulation d’une petite quantité d’informations. Les travaux de cette thèse portent sur le vieillissement normal de la MdeT et des fonctions de contrôle attentionnel (FCA) qui la sous-tendent (l’alternance, l’inhibition et la mise à jour). D’abord, la première étude (Chapitre II) visait à préciser l’effet du vieillissement normal sur la MdeT et sur chacune des FCA qui la sous-tendent. Elle avait également pour but d’identifier les FCA qui contribuent à la réalisation de différentes tâches de MdeT, et si cette contribution diffère selon le groupe d’âge. Des tâches mesurant chacune des FCA ainsi que des tâches de MdeT ont été administrées à des personnes âgées et à des jeunes adultes. Les analyses contrôlant pour le ralentissement cognitif ont révélé que les habiletés d’alternance et de mise à jour sont préservées chez les personnes âgées, mais que l’inhibition est atteinte comparativement aux jeunes adultes. Les analyses ont également montré que l’impact du vieillissement sur la MdeT dépend de la tâche utilisée. Enfin, les résultats ont indiqué que la contribution des FCA à la MdeT dépend à la fois de la tâche de MdeT et du groupe d’âge. En particulier, la mise à jour contribue davantage à la MdeT des personnes âgées qu’à celle des jeunes, ce qui pourrait refléter une tentative de compensation. La seconde étude (Chapitre III) avait pour objectif de caractériser la variabilité interindividuelle au niveau des FCA, pour les personnes âgées et pour les jeunes adultes. Des analyses hiérarchiques en grappes réalisées sur les habiletés d’alternance, d’inhibition et de mise à jour, ont permis de déterminer si différents profils de contrôle attentionnel étaient présents. L’étude cherchait également à déterminer si les individus appartenant à des profils de contrôle attentionnel distincts diffèrent quant à certaines variables intellectuelles ou de santé. Les analyses ont mis en évidence trois profils de contrôle attentionnel distincts parmi les personnes âgées, l’inhibition étant une FCA critique pour distinguer entre les trois sous-groupes. Trois profils de contrôle attentionnel ont également été identifiés chez les jeunes adultes, et ces profils étaient caractérisés par moins de variabilité intra-individuelle que ceux des âgés. Les analyses ont par ailleurs montré que les profils de contrôle attentionnel se distinguent sur certaines variables intellectuelles et de santé. Les implications théoriques et cliniques de ces résultats seront discutées en fin de thèse (Chapitre IV). / As the population is aging, it is increasingly important to study the changes that occur with advancing age. Normal aging is characterized by changes in various cognitive functions, such as working memory (WM), a limited capacity system that temporarily holds and manipulates a small quantity of information. The work presented in this thesis focused on the normal aging of WM and of the attentional control functions (ACFs) that underlie this system (shifting, inhibition, and updating). The first study (Chapter II) aimed at exploring the impact of normal aging on WM and on each of the ACFs. We also sought to determine which ACFs contribute to performance on different WM tests, and whether age group has an impact on those contributions. Tasks measuring each ACF as well as WM tasks were administered to healthy older adults and to younger adults. The analyses controlling for cognitive slowing revealed that older adults’ shifting and updating abilities are preserved, but that their inhibition abilities are impaired compared to younger adults. Moreover, the impact of normal aging on WM is task-dependent. The results also indicated that the relative contribution of the ACFs to WM depends on both the WM task used and the age group. In particular, older adults relied more than younger adults on updating to perform WM tasks, which might reflect a compensation attempt. The second study (Chapter III) aimed at characterizing interindividual variability in the ACFs of both older and younger adults. Cluster analyses were performed on the shifting, inhibition, and updating abilities, in order to determine whether different attentional control profiles were present. This study also explored whether the individuals that belonged to distinct attentional control profiles differed as to intellectual and health variables. The analyses revealed three attentional control profiles among older adults, and inhibition was the ACF for which the three profiles differed the most. Three attentional control profiles were also identified among younger adults, and their profiles were characterized by less intra-individual variability than those of older adults. The results also showed that individuals belonging to different attentional control profiles differed on some intellectual and health variables. The theoretical and clinical implications of those findings are discussed in Chapter IV.

Submitted by Sara Ribeiro (sara.ribeiro@ucb.br) on 2018-08-08T14:11:40Z No. of bitstreams: 1 ArilsonFernandesMendoncadeSousaTese2018.pdf: 5768876 bytes, checksum: 66d7e7ce78b9d2a4b54e615ac9d3282d (MD5) / Approved for entry into archive by Sara Ribeiro (sara.ribeiro@ucb.br) on 2018-08-08T14:11:52Z (GMT) No. of bitstreams: 1 ArilsonFernandesMendoncadeSousaTese2018.pdf: 5768876 bytes, checksum: 66d7e7ce78b9d2a4b54e615ac9d3282d (MD5) / Made available in DSpace on 2018-08-08T14:11:52Z (GMT). No. of bitstreams: 1 ArilsonFernandesMendoncadeSousaTese2018.pdf: 5768876 bytes, checksum: 66d7e7ce78b9d2a4b54e615ac9d3282d (MD5) Previous issue date: 2018-05-25 / Only two weeks of sprint interval training (SIT) has been shown to be associated with positive changes in aerobic capacity and cardiac autonomic control. Both aerobic capacity and autonomic control have been shown to be positively associated with improved attention. However, to date, the relationship between this type of training and attention has not been investigated yet. The aim of the present study was to investigate the influence of two weeks of SIT on aerobic capacity, cardiac autonomic control and attention components in healthy university students; Also, to verify if the training fidelity would influence these adaptations. One hundred and nine participants were divided into experimental (EG) and control (CG) groups. EG performed a SIT program consisting of 6 sessions of maximal 4 × 30 s all-out efforts on a cycle ergometer, interspersed with active 4-minute rests. The criterion for fidelity was to reach> 90% of the estimated maximum heart rate (HR) during sprint sessions. After analysis, EG was divided into fidelity groups HIGH (n = 26) and LOW (n = 46), respectively. The attention components were evaluated through the Attention Network Test (ANT). The aerobic capacity (VO2max) was estimated according to Astrand's nomogram while the sum of the skinfolds: pectoral, triceps, subscapular, medial axillary, abdomen, suprailiac and thigh was verified. Autonomic HR control was assessed by HR variability (HRV) and HR complexity at rest and during ANT, before and after six sessions of SIT. Both HIGH and LOW significantly increased aerobic capacity, vagal modulation before and during ANT and executive control, and decreased body fat after SIT (p <0.05). However, only HIGH participants showed an increase in HR complexity and accuracy in ANT responses when compared to LOW (p <0.05). Two weeks of SIT improved executive control, body fat, aerobic capacity and autonomic control in university students, with better results reported for the HIGH group. / Apenas duas semanas de treinamento intervalado de esforços supra máximos (TIsm) tem mostrado estar associado com modificações positivas na capacidade aeróbia e controle autonômico cardíaco. Tanto a capacidade aeróbia, como o controlo autonômico demonstram estar associados positivamente com melhoria da atenção. Entretanto, até o presente momento a relação entre este tipo de treinamento e atenção não foi investigada. O objetivo do presente estudo foi investigar a influência de um programa de TIsm na capacidade aeróbia, controle autonômico cardíaco e componentes da atenção em jovens universitários saudáveis; ainda, verificar se a fidelidade do treinamento influenciaria essas adaptações. Cento e nove participantes foram divididos em grupo experimental (GE) e controle (GC). O GE realizou um programa TIsm que consistiu em 6 sessões de TIsm de 4 × 30 s em um cicloergômetro, intercaladas com descansos ativos de 4 min. O critério para fidelidade foi atingir> 90% da frequência cardíaca máxima estimada (FC) durante as sessões de TIsm. Após as análises, o GE foi dividido em grupos de fidelidade alta, GEA (n = 26) e baixa, GEB (n = 46), respectivamente. Os componentes da atenção foram avaliados por meio do Teste de Rede de Atenção (ANT). A capacidade aeróbia (VO2max) foi estimada segundo o nomograma de Astrand enquanto o somatório de dobras cutâneas: peitoral, tríceps, subescapular, axilar média, abdômen, supra-ilíaca e coxa foi realizada. O controle autonômico da FC foi avaliado por meio da VFC e complexidade da FC em repouso e durante o ANT, antes e depois de seis sessões de TIsm. Ambos GEA e GEB aumentaram significativamente a capacidade aeróbia, modulação vagal antes e durante a realização do ANT e o controle executivo e diminuição da gordura corporal após o TIsm (p <0,05). No entanto, apenas os participantes do GEA apresentaram um aumento na complexidade da FC e acurácia nas respostas do ANT quando comparados ao GEB (p <0,05). Duas semanas de TIsm melhoraram o controle executivo, a gordura corporal, a capacidade aeróbia e o controle autonômico em estudantes universitários, com melhores resultados relatados para o grupo com GEA fidelidade.

The essays in this dissertation examine how political institutions affect economic development. In the first essay, I examine how executive control of the legislature shapes the time horizon of governing politicians and its effect on economic growth. The second essay examines how border changes over the past two centuries have provided different areas within modern countries with different institutional histories and how this affects the geographic concentration of economic activity. For the final essay, I examine whether elections have an effect on macroeconomic volatility when controlling for the democratic nature of the regime.

Mild traumatic brain injury (MTBI) has gained increasing attention over recent years with much research directed at the nature of persisting symptoms experienced by individuals with MTBI. Owing to the subtle nature of cognitive-communicative difficulties after MTBI, as well as the lack of sensitivity of traditional assessment tools in identifying these difficulties, individuals with MTBI are seldom referred for speech-language therapy services. The need has therefore arisen for the communicative abilities of individuals with MTBI to be assessed in ways other than through the implementation of traditional assessment tools. This preliminary study, for which a qualitative approach with a multiple case study design was adopted, aimed to investigate communication following MTBI from the perspective of a spouse. The spouses of three individuals with MTBI were selected to participate in this study. Semi-structured interviews consisting of two open-ended questions were held with each spouse. The content obtained from the interviews was subjected to a discourse analysis (DA) and the themes that were identified were interpreted within the Model of Social Communication (Hartley, 1995). The results of this study revealed that each of the participants perceived changes in the communication of their spouses since the MTBI. When interpreted within the Model of Social Communication (Hartley, 1995), these communication difficulties were considered to be either the result of impaired internal processes (including impairments in executive control, stored knowledge, subcortical and limbic input or cognition) or the interaction between these impaired internal processes and the environment. The implications of these results regarding the role of the speech-language therapist in MTBI are highlighted. The potential value of the spouse, and the use of DA as both a methodological and clinical tool in the field of speech-language therapy are discussed. Recommendations for future research are made. / Dissertation (M (Communication Pathology))--University of Pretoria, 2007. / Speech-Language Pathology and Audiology / M (Communication Pathology) / unrestricted

No description available.

Plasticity is a central concept within the life-span approach of development and is defined as the ability of an individual to change and reorganize in response to environmental challenges (e.g., Baltes & Singer, 20019. Such intraindividual changes can be induced by systematic cognitive training. Recent studies suggest that substantial amounts of plasticity can be induced in executive control functions with a process-based training approach. These newer studies show that repeated practice on executive control tasks not only improved performance on these trained tasks, but also led to improvements in nontrained tasks (i.e., transfer; e.g., Jaeggi, Buschkuehl, Jonides, & Perrig, 2008; Karbach & Kray, 2009). Executive control processes are especially relevant from a developmental perspective because executive control is involved in a wide range of complex cognitive activities (e.g., van der Sluis, de Jong, & van der Leij, 2007) and is one of the most central areas of cognitive development (e.g., Craik & Bialystok, 2006). The current thesis aimed at elucidating several important questions concerning the plasticity of executive control functions induced by systematic cognitive training. Firstly, the amount, range, and stability of plasticity in adolescents and older adults were investigated. Secondly, studies explored if training design, age, and interindividual differences moderate the amount and range of plasticity. Furthermore, the current thesis aimed at exploring how process-based training specifically leads to transfer effects. To explore these questions, all studies employed a pretest-posttest-design comparing a group of participants that was trained with a process-based training approach to a group of control partici-pants that did not receive the training. Pretraining and posttraining sessions incorporated systematic assessment of transfer measures in different cognitive domains. The first study set out to investigate if executive control can be trained in adolescents with a task switching training. Additionally, the study explored what particular domains of executive control may underlie training and transfer effects, and if acute bouts of exercise directly prior to cognitive training enhance training effects. Analyses indicated substantial training effects for both training groups (with or without acute exercise) and near transfer to a similar switching task. Other findings of transfer were limited to a speed task and a tendency for faster reaction times in an updating task. Thus, findings indicate, for the first time, that executive control can be enhanced in adolescents through a short training. Furthermore, analyses suggest that updating may be of particular relevance for the effects of the task switching training. Analyses revealed no additional effects of the exercise intervention. The second study set out to explore, for the first time, the effects of a process-based training ap-proach in old-old age (above 80 years). After ten sessions of practice on working memory tasks, the training group improved in four of the five trained tasks, emphasizing the potential for plasticity even in old-old age. The gains in the training group were largely driven by individuals who started out with a low capacity in the training tasks. Thus, findings suggest that working memory can be improved with a short executive control training even in old-old age, particularly for low-capacity individuals. The absence of transfer effects in this study may point to the limits of plasticity in this age group. The third study aimed at further elucidating the mixed findings regarding the amounts of training and transfer effects induced by executive control training in older adults. For that purpose, a sample of older adults covering a wide range from young-old to old-old age (65 to 95 years) was either trained for nine sessions on a visuospatial and a verbal working memory as well as an executive control task; or served as controls. Analyses revealed significant training effects in all three trained tasks, as well as near transfer to verbal working memory and far transfer to a nonverbal reasoning task. Remarkably, all training effects and the transfer effect to verbal working memory were even stable at a nine-month follow-up. These findings suggest that cognitive plasticity is preserved over a large range of old age and that even a rather short training regimen can lead to (partly specific) training and transfer effects. However, analyses also revealed that there are a range of factors that may moderate the amount of plasticity, e.g., age and baseline performance in the training domain. To summarize, the current thesis explored effects of short executive control trainings on cognitive functions in adolescents and older adults. The findings suggest a high potential for intraindividual variability across the whole life-span. Plasticity was shown on the level of training and transfer tasks, as well as on the level of stability of effects. Furthermore, results support the notion that process-based training improves executive control processes that in turn lead to improvements in tasks that rely on these processes. The current thesis makes important contributions to the conceptual debate about the potentials and limits of training-induced plasticity across the life-span. It benefits the debate in that it specifically delineates factors that moderate the obtained effects.:Abstract ..............................................................................................1 1 General Introduction .....................................................................3 1.1 Plasticity of cognitive functions ...................................................5 1.2 Executive control functions .........................................................6 1.3 Cognitive training of executive control functions .......................9 2 Outline and Central Questions ......................................................19 2.1 What amount of plasticity does executive control training induce in different age groups? .........................................................................19 2.2 Do training and transfer effects of executive control training remain stable over time? ....................................................................20 2.3 Do training design, age, and baseline performance moderate the amount of plasticity? ...........................................................................20 2.4 Are changes in trained tasks specifically related to changes in transfer tasks? .................................................................................21 3 Study 1 - Effects of a Task Switching Training in Adolescents .......22 3.1 Introduction ..............................................................................22 3.2 Methods ....................................................................................27 3.3 Results ......................................................................................33 3.4 Discussion .................................................................................43 4 Study 2 - Effects of a Working Memory Training in Old-Old adults .48 4.1 Introduction ...............................................................................48 4.2 Methods .....................................................................................51 4.3 Results .......................................................................................54 4.4 Discussion ..................................................................................59 5 Study 3 - Factors Moderating Effects of Working Memory Training in Older Adults .......................................................................63 5.1 Introduction ................................................................................63 5.2 Methods ......................................................................................67 5.3 Results .........................................................................................71 5.4 Discussion ...................................................................................78 6 General Discussion .........................................................................83 6.1 Summary of empirical findings .....................................................83 6.2 Integration of the main empirical findings ...................................85 6.3 Conclusion and Outlook ...............................................................95 6.4 Summary ......................................................................................98 References ..........................................................................................99 Appendix ............................................................................................112