The role of dysfunctional expectation persistence in psychopathology

In the literature, expectations are seen as core elements influencing and directing human behavior. There are many different models underlying this, such as the well-known expectancy–value theories. The past few decades have seen increased interest in analyzing the role of these theories in psychotherapy. On one hand, scholars have found increasingly convincing evidence of the impact of expectations on treatment success (i.e., placebo-effect research). On the other hand, the question has arisen whether people with mental disorders differ in the content of their expectations as well as in their processing mechanisms. The ViolEx model is one of the first expectation models that has been applied to the mechanisms of psychopathology and psychotherapy. It appears that people with mental disorders not only show a greater amount of dysfunctional expectations but also that those expectations are more persistent than in people without a mental disorder. In addition to other mechanisms, the concept of “cognitive immunization” has been suggested as responsible for the maintenance of dysfunctional expectations. First, researchers have found evidence for the link between cognitive immunization (i.e., expectation persistence after an expectation-disconfirming experience) and psychopathology. For this dissertation, the process of cognitive immunization, as a relatively new concept, was analyzed in detail, with the goal of developing interventions and reducing cognitive immunization processes. In the first study, the concept of cognitive immunization was analyzed in an experimental design (N = 102). Social expectations were induced and violated, and the expectation adaptation was hypothesized to differ between micro-interventions, including an expectation- focused psychological intervention (EFPI). The EFPI group showed significantly greater variability in their expectations and, thus, lower rates of cognitive immunization compared to the other groups. Second, the complexity of the implicit operationalization of cognitive immunization through experimental designs showed the need for efficient (self-rating) instruments. Therefore, a self-rating questionnaire, the Immunization Scale (IMS), has been developed. The IMS was validated through exploratory (N = 230) and confirmatory (N = 299) factor analyses, resulting in a 23-item questionnaire. In the third study, the EFPI was tested for its effectiveness in reducing cognitive immunization, measured with the IMS. Therefore, an online longitudinal randomized controlled design was developed for people with mild depressive and/or anxiety symptoms (N = 128). Cognitive immunization was correlated with psychopathology, and the EFPI group showed a significant reduction in the cognitive immunization level. Lastly, and based on the third study, a protocol paper was written for a large-scale psychotherapeutic study that analyzes the effectiveness of cognitive behavioral therapy (CBT) with the integration of EFPIs in people with diagnosed depression compared to standard CBT without special focus on expectations. This dissertation provides a validated questionnaire to analyze cognitive immunization processes and their link to psychopathology. It offers initial evidence of EFPIs’ effectiveness in reducing cognitive immunization in people with psychopathological symptoms. Practical and research implications are discussed

A New Mathematical Model for Evolutionary Games on Finite Networks of Players

A new mathematical model for evolutionary games on graphs is proposed to extend the classical replicator equation to finite populations of players organized on a network with generic topology. Classical results from game theory, evolutionary game theory and graph theory are used. More specifically, each player is placed in a vertex of the graph and he is seen as an infinite population of replicators which replicate within the vertex. At each time instant, a game is played by two replicators belonging to different connected vertices, and the outcome of the game influences their ability of producing offspring. Then, the behavior of a vertex player is determined by the distribution of strategies used by the internal replicators. Under suitable hypotheses, the proposed model is equivalent to the classical replicator equation. Extended simulations are performed to show the dynamical behavior of the solutions and the potentialities of the developed model.Comment: 26 pages, 7 figures, 1 tabl

Understanding responses to environments for the Prisoner's Dilemma: A meta analysis, multidimensional optimisation and machine learning approach

This thesis investigates the behaviour that Iterated Prisoner’s Dilemma strategies should adopt as a response to different environments. The Iterated Prisoner’s Dilemma (IPD) is a particular topic of game theory that has attracted academic attention due to its applications in the understanding of the balance between cooperation and com petition in social and biological settings. This thesis uses a variety of mathematical and computational fields such as linear al gebra, research software engineering, data mining, network theory, natural language processing, data analysis, mathematical optimisation, resultant theory, markov mod elling, agent based simulation, heuristics and machine learning. The literature around the IPD has been exploring the performance of strategies in the game for years. The results of this thesis contribute to the discussion of successful performances using various novel approaches. Initially, this thesis evaluates the performance of 195 strategies in 45,600 computer tournaments. A large portion of the 195 strategies are drawn from the known and named strategies in the IPD literature, including many previous tournament winners. The 45,600 computer tournaments include tournament variations such as tournaments with noise, probabilistic match length, and both noise and probabilistic match length. This diversity of strategies and tournament types has resulted in the largest and most diverse collection of computer tournaments in the field. The impact of features on the performance of the 195 strategies is evaluated using modern machine learning and statistical techniques. The results reinforce the idea that there are properties associated with success, these are: be nice, be provocable and generous, be a little envious, be clever, and adapt to the environment. Secondly, this thesis explores well performed behaviour focused on a specific set of IPD strategies called memory-one, and specifically a subset of them that are considered extortionate. These strategies have gained much attention in the research field and have been acclaimed for their performance against single opponents. This thesis uses mathematical modelling to explore the best responses to a collection of memory-one strategies as a multidimensional non-linear optimisation problem, and the benefits of extortionate/manipulative behaviour. The results contribute to the discussion that behaving in an extortionate way is not the optimal play in the IPD, and provide evidence that memory-one strategies suffer from their limited memory in multi agent interactions and can be out performed by longer memory strategies. Following this, the thesis investigates best response strategies in the form of static sequences of moves. It introduces an evolutionary algorithm which can successfully identify best response sequences, and uses a list of 192 opponents to generate a large data set of best response sequences. This data set is then used to train a type of recurrent neural network called the long short-term memory network, which have not gained much attention in the literature. A number of long short-term memory networks are trained to predict the actions of the best response sequences. The trained networks are used to introduce a total of 24 new IPD strategies which were shown to successfully win standard tournaments. From this research the following conclusions are made: there is not a single best strategy in the IPD for varying environments, however, there are properties associated with the strategies’ success distinct to different environments. These properties reinforce and contradict well established results. They include being nice, opening with cooperation, being a little envious, being complex, adapting to the environment and using longer memory when possible